Systems and methods for diagnosing stuck ATWU valve

Methods and systems are provided for diagnosing a stuck Active Transmission Warmup (ATWU) valve. In one example, a method for an ATWU valve monitoring routine of a vehicle comprises determining a temperature difference between an engine coolant temperature (ECT) and a transmission fluid temperature (TFT) over a duration before the ATWU valve is commanded from a closed position to an open position or from the open position to the closed position comparing a rate of change of the TFT before and after the ATWU valve is commanded to the open position or the closed position; and indicating a stuck ATWU valve based on at least one of the temperature difference, the TFT rate of change comparison, or a combination thereof, based on a calibration parameter.

FIELD

The present description relates generally to methods and systems for diagnosing a stuck Active Transmission Warmup (ATWU) valve of a vehicle.

Vehicles may include cooling systems configured to reduce overheating of an engine by transferring the heat to ambient air. Therein, coolant is circulated through the engine block to remove heat from the hot engine, and the heated coolant is then circulated through a radiator near the front of the vehicle. Heated coolant may also be circulated through a heat exchanger to heat a passenger compartment. The cooling system may include various components such as various valves and one or more thermostats.

While vehicles may include cooling systems to reduce overheating of the engine, it may additionally be understood that various vehicle systems tend to operate most efficiently when in an optimal temperature range. For example, operating a transmission of a vehicle above a threshold temperature may present durability complications, while operating the transmission below the threshold temperature may result in degraded efficiency. To help maintain the transmission within a desired temperature range, the vehicle may include an Active Transmission Warmup (ATWU) valve, which may be opened to expand an engine coolant loop to divert warm engine coolant to the transmission. The ATWU valve may be actuated in accordance with a control strategy that ensures that heat is directed efficiently and in a balanced manner throughout the coolant loop, to warm the engine, the transmission, a cabin of the vehicle, and/or other vehicle components.

Under some circumstances, the ATWU valve may become stuck in either a closed position or an open position, reducing an efficiency of the transmission, engine, and/or the vehicle. If a stuck ATWU valve can be detected, it may be desirable to adjust one or more operating conditions of the engine and/or vehicle to maintain the efficiency of the transmission, engine, and or vehicle and reduce degradation. For example, an acceleration of the vehicle may be limited if the ATWU valve is stuck.

In various examples, the ATWU valve may be diagnosed as being stuck. For example, U.S. Pat. No. 8,683,854B2 to Pursifull et al. teaches diagnosing a stuck ATWU valve by comparing a first temperature of coolant flowing in a first loop including the transmission with a second temperature of coolant flowing in a second loop not including the transmission. If after a duration following actuation of the ATWU valve, the first temperature exceeds a threshold temperature, a stuck ATWU valve may be indicated. Further, U.S. Pat. No. 9,022,647B2 to Jentz et al. teaches increasing an accuracy of ATWU valve diagnoses by comparing temperatures of coolant at different portions of a coolant loop based on states of different valves of the coolant loop.

However, the inventors herein have recognized potential issues with such an approach. Specifically, the methods may not be sufficient to indicate a stuck ATWU valve during a cold start, which may reduce an efficiency of engine warmup and increase an amount of time taken for the engine to reach optimal operating conditions. As a result, an opportunity exists for developing more robust diagnostics for monitoring and diagnosing a stuck ATWU valve.

The inventors herein have recognized these issues, and have developed systems and methods to at least partially address the above issues. In one example, a method for an ATWU valve monitoring routine of a vehicle comprises, determining a temperature difference between an engine coolant temperature (ECT) and a transmission fluid temperature (TFT) over a duration before the ATWU valve is commanded from an open position to a closed position or from the closed position to the open position; comparing a rate of change of the TFT before and after the ATWU valve is commanded to the open position or the closed position; and indicating a stuck ATWU valve based on at least one of the temperature difference, the TFT rate of change comparison, or a combination thereof, based on a calibration parameter. For example, a vehicle engine may be started in cold weather. When the engine is started, engine coolant may begin to circulate through a coolant loop of the vehicle. The engine coolant may be routed to a heat exchanger, where heat from the engine absorbed by the engine coolant is transferred to air that is blown into a cabin of the vehicle to warm occupants of the vehicle. When the engine coolant reaches a threshold temperature, an ATWU valve positioned on the coolant loop may be actuated to an open position. When the ATWU valve is actuated to the open position, the engine coolant may be routed to a second heat exchanger, where heat from the engine coolant may be transferred to transmission fluid circulating through a transmission of the vehicle. In this way, the transmission fluid may more rapidly reach an optimal TFT for the functioning of the transmission, increasing an efficiency of the vehicle. However, when the ATWU valve is actuated to the open position, if the ATWU valve does not open and remains stuck in the closed position, heat from the engine coolant may not be transferred to the transmission fluid, whereby the optimal TFT may not be achieved.

A valve monitoring routine may be regularly performed to diagnose the stuck ATWU valve. The valve monitoring routine may include the first algorithm (referred to herein as the ECT/TFT delta algorithm) and the second algorithm (referred to herein as the TFT slope delta algorithm). When the valve monitoring routine performs the first algorithm, a temperature5difference between the ECT and the TFT is measured before the ATWU valve is commanded open, where the temperature difference is determined by comparing an area integral between an ECT curve and a TFT curve. If an expected decrease in the temperature difference is detected, it may be inferred that heat is being transferred to the transmission fluid, whereby the first algorithm may indicate that the ATWU valve is open (e.g., stuck in open position). If the expected decrease in temperature difference is not detected, it may be inferred that heat is not being transferred to the transmission fluid, whereby the first algorithm may indicate that the ATWU valve is closed (e.g., operating as expected).

When the valve monitoring routine performs the second algorithm, a rate of change of the TFT measurements (e.g., a slope of a curve defined by the TFT measurements) is calculated over a first duration prior to opening the ATWU valve, and over a second, equal duration after opening the ATWU valve. If a difference between a first TFT slope prior to opening the ATWU valve and a second TFT slope after opening the ATWU valve (e.g., the TFT slope delta) exceeds a threshold value, it may be inferred that additional heat is being transferred to the transmission fluid after the valve is commanded open, whereby the second algorithm may indicate that the ATWU valve is open (e.g., operating as expected). If the TFT slope delta does not exceed the threshold value, it may be inferred that no additional heat is being transferred to the transmission fluid after the valve is commanded open, whereby the second algorithm may indicate that the ATWU valve is stuck (e.g., stuck in a closed position or open position). The valve monitoring routine may diagnose a stuck ATWU valve based on either or both of the first (ECT/TFT delta) algorithm and the second (TFT slope delta) algorithm, based on a calibration parameter of the valve monitoring routine. In this way, a procedure is provided for diagnosing the stuck ATWU valve that may be more robust than current approaches. An additional advantage of the systems and methods described herein is that the procedure may be implemented in a controller of the vehicle, and may rely on already existing sensors and other components of the vehicle, whereby a cost of implementation may not be high.

DETAILED DESCRIPTION

The following description relates to systems and methods for diagnosing a stuck Active Transmission Warmup (ATWU) valve of a vehicle cooling system, such as the vehicle cooling system depicted inFIG.1A. The vehicle cooling system may include a transmission warming system, as depicted inFIG.1B. The stuck ATWU valve may be diagnosed by performing a monitoring routine described in reference toFIGS.2-7B. Specifically,FIG.2shows a high-level method followed by the monitoring routine, whereFIGS.3and4show methods for determining whether conditions are met for running the monitoring routine and aborting the monitoring routine, respectively. Determining whether the conditions are met for running the monitoring routine may rely on a timer achieving a threshold value, as depicted in the method ofFIG.5. A first method for diagnosing the stuck ATWU valve depicted inFIG.6is based on determining a difference in temperatures of an engine cooling system of the vehicle and a transmission cooling system of the vehicle when the ATWU valve is closed after a cold start. A second method for diagnosing the stuck ATWU valve depicted inFIGS.7A and7Bindicates the stuck ATWU valve based on a change in an average slope of a transmission fluid temperature (TFT) prior to and after opening the ATWU valve during the cold start. In various embodiments, the monitoring routine may rely on a result of the first method matching a result of the second method. Example timelines for performing the monitoring routine when the ATWU valve is operating as expected and stuck closed are shown inFIGS.8A and8B, respectively.

FIG.1Ashows an example embodiment of a vehicle system100including a vehicle cooling system101in a motor vehicle102. Vehicle102has drive wheels106, a passenger compartment104(herein also referred to as a passenger cabin), and an under-hood compartment103. Under-hood compartment103may house various under-hood components under the hood (not shown) of motor vehicle102. For example, under-hood compartment103may house internal combustion engine10. Internal combustion engine10has a combustion chamber which may receive intake air via intake passage44and may exhaust combustion gases via exhaust passage48. Engine10as illustrated and described herein may be included in a vehicle such as a road automobile, among other types of vehicles. While the example applications of engine10will be described with reference to a vehicle, it should be appreciated that various types of engines and vehicle propulsion systems may be used, including passenger cars, trucks, etc.

Under-hood compartment103may further include cooling system101, which may circulate coolant through internal combustion engine10to absorb waste heat, and may distribute the heated coolant to radiator80, heater core90, exhaust gas recirculation (EGR) cooler31, turbo center housing32, urea injector33, transmission oil cooler125, automatic transmission warm-up (ATWU) heat exchanger34, engine oil cooler35, and coolant degas bottle37. In one example, cooling system101may be coupled to engine10and may circulate engine coolant from engine10to the various components described above via engine-driven water pump86, and back to engine10via various coolant lines. An engine coolant temperature (ECT) sensor26may be coupled to engine10, and may be configured to measure the temperature of engine coolant. Readings from ECT sensor26may then be communicated to an engine controller12. Engine-driven water pump86may be coupled to the engine via front end accessory drive (FEAD)36, and rotated proportionally to engine speed via a belt, chain, etc. (illustrated by line5). Specifically, engine-driven pump86may circulate coolant through passages in the engine block, head, etc., to absorb engine heat, which is then transferred via the radiator80to ambient air. In one example, where pump86is a centrifugal pump, the pressure (and resulting flow) produced by the pump may be increased with increasing crankshaft speed, which in the example ofFIG.1A, may be directly linked to the engine speed. As will be discussed in further detail below, coolant may be selectively circulated to the various components based on vehicle operating conditions and coolant temperature.

The temperature of the coolant, and coolant flow path(s) may be regulated at least in part by a first thermostat38. First thermostat38may include a temperature sensing element41, such as a wax element, for example. Further, first thermostat38may include a first thermostat valve42located at a junction between coolant lines82,83, and84. Based on a temperature of the coolant as sensed by the temperature sensing element41, first thermostat valve42may be in one of three positions. For example, in a first position, first thermostat valve42may enable coolant to flow from coolant line82, into coolant line83(also referred to herein as bypass line83), while preventing coolant flowing from coolant line82to coolant line84. In a second position, first thermostat valve42may enable coolant to flow from coolant line82into both bypass line83and coolant line84. Thus, in the second position, coolant may be enabled to flow through the bypass line83in addition to enabling coolant to flow to the radiator80. In a third position, first thermostat valve42may enable coolant to flow from coolant line82to coolant line84, while preventing coolant flowing into bypass line83.

One or more blowers (not shown) and cooling fans may be included in cooling system101to provide airflow assistance and augment a cooling airflow through the under-hood components. For example, cooling fan92, coupled to radiator80, may be operated to provide cooling airflow assistance through radiator80. Cooling fan92may draw a cooling airflow into under-hood compartment103through an opening in the front-end of vehicle102, for example, through grill shutter system112. Such a cooling air flow may then be utilized by radiator80and other under-hood components (e.g., fuel system components, batteries, etc.) to keep the engine and/or transmission cool. Further, the air flow may be used to reject heat from a vehicle air conditioning system. Further still, the airflow may be used to increase the performance of a turbocharged/supercharged engine that is equipped with intercoolers that reduce the temperature of the air that goes into the intake manifold/engine. In one example, grill shutter system112may be configured with a plurality of louvers (or fins, blades, or shutters) wherein a controller may adjust a position of the louvers to control an airflow through the grill shutter system.

Cooling fan92may be coupled to, and driven by, engine10, via alternator72and system battery74. Cooling fan92may also be mechanically coupled to engine10via an optional clutch (not shown). During engine operation, the engine-generated torque may be transmitted to alternator72along a drive shaft (not shown). The generated torque may be used by alternator72to generate electrical power, which may be stored in an electrical energy storage device, such as system battery74. Battery74may then be used to operate an electric cooling fan motor94.

Vehicle system100may further include a transmission40for transmitting the power generated at engine10to vehicle wheels106. Transmission40, including various gears and clutches, may be configured to reduce the high rotational speed of the engine to a lower rotational speed of the wheel, while increasing torque in the process. To enable temperature regulation of the various transmission components, cooling system101may also be communicatively coupled to a transmission cooling system45. The transmission cooling system45includes a transmission oil cooler125(or oil-to-water transmission heat exchanger) located internal or integral to the transmission40, for example, in the transmission sump area at a location below and/or offset from the transmission rotating elements. Transmission oil cooler125may have a plurality of plate or fin members for maximum heat transfer purposes. Coolant from coolant line85may communicate with transmission oil cooler125via conduit87. In some examples, a transmission fluid temperature (TFT) sensor27may be coupled to transmission40, and may be configured to monitor temperature of transmission fluid, and communicate the temperature of the transmission fluid to controller12. In some examples, coolant may flow from the radiator to the transmission oil cooler (not shown).

In some examples, coolant may flow through coolant line85to heater core90via conduit81, where the heat may be transferred to passenger compartment104. Specifically, heater core90, which may be configured as a water-to-air heat exchanger, may exchange heat with the circulating coolant and transfer the heat to the vehicle passenger compartment104based on operator heating demands. As such, heater core may also be coupled to a vehicle HVAC system (or heating, ventilation, and air conditioning system) that includes other components such as a heater fan, and an air conditioner (not shown).

In some examples, coolant may flow through coolant line85to engine oil cooler35. Engine oil cooler35may comprise a heat exchanger, in some examples. For example, engine oil may be fed to the engine oil cooler such that the engine oil flows through tubes of the engine oil cooler, while engine coolant flows around the tubes. As such, heat from the oil may be transferred through the walls of the tubes to the surrounding coolant.

In some examples, coolant may flow through coolant line82, and to coolant degas bottle37, via conduit89. Degas bottle37may allow entrained air and gasses in the coolant to be separated from the coolant as the coolant flows through the degas tank. In some examples there may be a vent line191from radiator80to degas bottle37. A vent line check valve190may be included in vent line191in some examples, to prevent air from being pulled into radiator80. However, in other examples, vent line191and vent line check valve190may not be included in cooling system101.FIG.1Afurther shows a control system14. Control system14may be communicatively coupled to various components of engine10to carry out the control routines and actions described herein. For example, as shown inFIG.1A, control system14may include an electronic digital controller12. Controller12may be a microcomputer, including a microprocessor unit, input/output ports, an electronic storage medium for executable programs and calibration values, random access memory, keep alive memory, and a data bus. As depicted, controller12may receive input from a plurality of sensors16, which may include user inputs and/or sensors (such as transmission gear position, gas pedal input, brake input, transmission selector position, vehicle speed, vehicle acceleration, vehicle attitude, engine speed, mass airflow through the engine, ambient temperature, intake air temperature, etc.), cooling system sensors (such as coolant temperature, transmission fluid temperature, coolant level, coolant level sensor circuit board temperature, cylinder heat temperature, fan speed, passenger compartment temperature, ambient humidity, thermostat output, etc.), and others. Further, controller12may communicate with various actuators18, which may include engine actuators (such as fuel injectors, an electronically controlled intake air throttle plate, spark plugs, etc.), cooling system actuators (such as the various valves of the cooling system), and others. In some examples, the storage medium may be programmed with computer readable data representing instructions executable by the processor for performing the methods described below as well as other variants that are anticipated but not specifically listed.

Furthermore, the temperature of the coolant, and coolant flow path(s), may be regulated at least in part by a second thermostat61. Second thermostat61may include a second temperature sensing element62, such as a wax element, for example. Second thermostat61may further include a second thermostat valve63, located at a junction between coolant lines81a,83,84a, and24a. As illustrated, coolant line24amay receive coolant flow from one or more of coolant lines87a,85a, and89a. Second thermostat valve63may be configured in various positions, to enable coolant to return to pump86via one or more of coolant lines83,84a,81a, and24. In some embodiments, second thermostat61may comprise an electrically-heated thermostat, where electricity may be provided to second thermostat61via an electrical energy storage device, such as system battery74. For example, in addition to the mechanical function of the wax element, second thermostat61may comprise an electric heater25. Electric heater25may be controlled by the vehicle controller12, where the controller may receive information on engine speed, load, transmission fluid temperature (TFT), etc. Said another way, a data set, or “map”, may be stored at the controller, which may dictate when and how heat is added to the electrically-heated thermostat to ensure optimal engine performance. A position sensor28may be coupled to second thermostat valve63, such that an accurate indication of what position the valve is in can be communicated to the vehicle controller.

In some examples, coolant may flow through coolant line85to active transmission warm-up (ATWU) heat exchanger34, via conduit88. For example, it may be desirable to heat transmission oil with engine coolant to warm up the transmission oil quickly, such that the transmission pumps oil more easily as compared to when it is cold. For illustrative purposes, oil flow from the transmission40into and away from the Transmission heat exchanger34, is represented by arrows21. The Transmission heat exchanger34may comprise a plate-fin design, as an example. Because the Transmission heat exchanger34utilizes engine coolant as the heat exchange fluid, transmission fluid temperature may operate at roughly the equivalent of engine temperature. Furthermore, in some examples, an ATWU bypass valve22may be positioned in conduit88, and may be regulated by a controller12in a control system14. For example, Transmission heat exchanger34may in some examples be bypassed (e.g. bypass valve22commanded closed). Such examples may include conditions where hot coolant is needed for cabin heating, which may occur at cold ambient temperatures (e.g. close to zero degrees F.). At warmer ambient temperatures, the ATWU bypass valve (also referred to herein as ATWU valve)22may be commanded open for transmission oil warming as soon as the transmission is put into drive.

As an example of how ATWU valve22is used, vehicle102may be started when engine10and other components of vehicle102are cold, for example, after a period of time during which vehicle102is not in use (e.g., a cold start). When engine10starts, coolant may begin to circulate throughout the coolant loop described above including conduits81,82,83,84,85,24b, and24c. The coolant may be heated by engine10. As a temperature of the coolant increases, heat from the coolant may be extracted and transferred to air by heater core90, which may be blown into passenger compartment104to warm occupants of vehicle102. Additionally, ATWU valve22may be commanded open, allowing the heated coolant to circulate through transmission heat exchanger34via conduits88and88a. As the heated coolant circulates through heat exchanger34, heat is extracted from the coolant and transferred to transmission fluid circulating through transmission40. As the transmission fluid warms up, an efficiency of the transmission increases. To achieve a balance between warming the occupants and warming the transmission fluid (and/or other components of vehicle102), ATWU valve22may be actuated by controller12in accordance with one or more control strategies. The one or more control strategies may be based on measured temperatures at various sensors of vehicle102, including first thermostat38, second thermostat61, an in-cabin temperature sensor56, an external temperature sensor58, and/or other sensors. A first control strategy may include commanding ATWU valve22open at an engine start event, and adjusting a position of ATWU valve22as the coolant heats up. A second control strategy may include ATWU valve22being closed at engine start, and commanding ATWU valve22open in response to a temperature of the coolant achieving a threshold temperature. Various other control strategies may additionally or alternatively be used, without departing from the scope of this disclosure.

In one example, ATWU valve22may comprise a normally open solenoid valve that may be actuated closed to increase coolant warmup, for example, to increase an amount of heat generated in passenger compartment104. In such embodiments, controller12may send a signal to ATWU valve22, actuating ATWU valve22to a closed position. Alternatively, ATWU valve22may comprise a normally closed solenoid valve that prioritizes coolant warmup, which may be actuated open to warm up the transmission fluid. In such embodiments, controller12may send a signal actuating ATWU valve22to the open position.

Under some circumstances, ATWU valve22may become stuck, either in an open position or in a closed position, which may render the control strategies ineffective. If ATWU valve22is stuck in an open position during the cold start, a temperature of the transmission fluid (TFT) may be equal to an engine coolant temperature (ECT), whereby the TFT and the ECT may increase at the same rate. As the TFT and the ECT increase at the same rate, the transmission fluid may overheat, reducing an efficiency of transmission40. Additionally, an amount of heat available to heat passenger compartment104may be reduced, resulting in discomfort for occupants of vehicle102. Alternatively, if ATWU valve22is stuck in a closed position during the cold start, the transmission fluid may not be warmed to an optimal operating temperature, or may be warmed at a slower rate, reducing an efficiency of the transmission. As a result, one or more monitoring routines may be performed to monitor ATWU valve22to determine whether ATWU valve22is stuck. If ATWU valve22is determined by the one or more monitoring routines to be stuck, a malfunction indicator lamp (MIL)59of passenger compartment104may be illuminated.

FIG.1Bshows a simplified cooling system150, which may be a simplified version of cooling system101ofFIG.1A. Simplified cooling system150includes an engine154(e.g., engine10ofFIG.1A) and a transmission159. Transmission159includes a torque converter157, where torque converter157rotates a turbine shaft158based on a rotation of the crankshaft156of engine154. In a first coolant loop161, coolant is circulated through a conduit162and a conduit164to a radiator160, which may cool the coolant heated by engine154. First coolant loop161may be a simplified version of the coolant loop formed by conduits81,82,83,84,85, and24ofFIG.1A. A thermostat182may measure a temperature of the coolant, and if the temperature of the coolant is below a threshold temperature (e.g. 80° C.) a thermostat valve183may be closed. More specifically, a thermostat temperature sensing element of thermostat182may be exposed to circulating engine coolant, and as a result of the ECT being below a threshold temperature, thermostat valve183may be commanded to a closed position. As a result of the ECT rising above the threshold temperature, thermostat valve183may transition from the closed position to an open position. When thermostat valve183is closed, the coolant may circulate back to engine154without circulating through radiator160, to conserve the heat in the coolant and accelerate a warm-up of engine154.

Cooling system150also includes a transmission coolant loop165, where a transmission fluid is circulated by a pump195, from a sump tank194to transmission159via a conduit168. The transmission fluid is heated as it passes through transmission159. The heated transmission fluid exits transmission159via a conduit167of transmission coolant loop165, and is flowed into a transmission heat exchanger180, prior to being routed back to sump tank194via a conduit166.

First coolant loop161is connected to transmission coolant loop165via a second coolant loop163, where a flow of coolant through a conduit169(e.g., conduit88ofFIG.1A) is controlled by an ATWU valve184(e.g., ATWU valve22ofFIG.1A). Thus, when ATWU valve184is closed, the coolant circulates through conduits162and164of first coolant loop161and does not circulate through second coolant loop163. Alternatively, when ATWU valve184is commanded open, the coolant is flowed to transmission heat exchanger180via a conduit171, where heat in the coolant may be transferred to the transmission fluid (e.g., to warm up transmission159). The coolant may circulate both back to engine154via first coolant loop161, and through coolant loop163concurrently. In this way, a position of ATWU valve184may be controlled to adjust an amount of heat transferred to the transmission fluid at heat exchanger180. If a temperature of the transmission fluid (TFT) is below an optimal threshold temperature, ATWU valve184may be adjusted to a more open position to increase the amount of heat transferred to the transmission fluid at heat exchanger180. The TFT may be measured at a TFT sensor185positioned on conduit168. If the TFT is at or above the optimal threshold temperature, ATWU valve184may be adjusted to a more closed position, to decrease the amount of heat transferred to the transmission fluid at heat exchanger180. In various embodiments, ATWU valve184may be closed until the engine coolant achieves a threshold temperature for optimal performance (e.g., 70° C.). After the threshold temperature is achieved, ATWU valve184may be opened to transfer heat from the engine coolant to the transmission fluid.

As described above, ATWU valve184may be actuated in accordance with a control strategy to maximize a performance and/or efficiency of various components of the vehicle. Because an efficient operation of transmission159(e.g., transmission40ofFIG.1A) may rely on ATWU valve184operating in an expected manner, a controller (e.g., controller12) may monitor a performance of ATWU valve184to determine whether ATWU valve184is operating in the expected manner. Monitoring the performance of ATWU valve184may include performing one or more monitoring routines at regular intervals, such as the monitoring routine described below in reference toFIG.2.

Turning now toFIG.2, an example method200is shown for performing a monitoring routine to evaluate a performance of an ATWU valve of a vehicle, such as ATWU valve22of vehicle102ofFIG.1Aand/or ATWU valve184ofFIG.1B. By performing the monitoring routine, a stuck ATWU valve may be detected, which may reduce an efficiency of an engine and/or a transmission of the vehicle during warmup after a cold start. Method200and other methods described herein are described with reference to the systems described herein and shown inFIGS.1A and1B, though it should be understood that similar methods may be applied to other systems without departing from the scope of this disclosure. Parts of method200may be carried out by a controller, such as controller12inFIG.1A, and may be stored at the controller as executable instructions in non-transitory memory. Instructions for carrying out method200and the rest of the methods included herein may be executed at least in part by the controller based on instructions stored on a memory of the controller and in conjunction with signals received from sensors of the engine system, such as the sensors described above with reference toFIGS.1A and/or1B. The controller may employ coolant system actuators according to the methods depicted below.

Method200begins at202, where method200includes evaluating operating conditions of the vehicle. Operating conditions may be estimated, measured, and/or inferred, and may include one or more vehicle conditions, such as vehicle speed, vehicle location, etc., various engine conditions, such as engine status, engine load, engine speed, A/F ratio, etc., various fuel system conditions, such as fuel level, fuel type, fuel temperature, etc., various evaporative emissions system conditions, such as fuel vapor canister load, fuel tank pressure, etc., as well as various ambient conditions, such as ambient temperature, humidity, barometric pressure, etc. Evaluating the operating conditions of the vehicle may include determining whether an engine of the vehicle has been turned on and/or is operating. Evaluating the operating conditions of the vehicle may further include determining a temperature of an engine coolant and/or a transmission fluid of the vehicle at one or more locations within various coolant loops used to control a temperature of the engine coolant and/or transmission fluid.

At204, at the200includes determining whether entry conditions are met for performing the monitoring routine. Determining whether conditions are met for performing the monitoring routine is described in greater detail below, in reference toFIG.3.

If at204it is determined that the conditions are not met for performing the monitoring routine, but the200proceeds to205. At205, method200includes maintaining operating conditions until the conditions are met for performing the monitoring routine. If at204it is determined that the conditions are met for performing the monitoring routine, and the200proceeds to206.

At206, method200may include performing an ECT/TFT delta algorithm, where the ECT/TFT delta algorithm is based on comparing an ECT with a TFT during the cold start event. Performing the ECT/TFT delta algorithm is described in greater detail below in reference toFIG.6.

At208, method200may include performing a TFT slope delta algorithm, where the TFT slope delta algorithm is based on comparing a first rate of change in a slope of the TFT when the ATWU valve is closed with a second rate of change in a slope of the TFT when the ATWU valve is open. Performing the TFT slope delta algorithm is described in greater detail below in reference toFIGS.7A and7B.

The performance of the ATWU valve may be assessed and a stuck ATWU valve may be diagnosed based on a result of either or both of the ECT/TFT delta algorithm and the TFT slope delta algorithm. In other words, in some embodiments, the ECT/TFT delta algorithm may be performed and the TFT slope delta algorithm may not be performed, where the performance of the ATWU valve may be assessed based on the ECT/TFT delta algorithm and not the TFT slope delta algorithm. In other embodiments, the TFT slope delta algorithm may be performed and the ECT/TFT delta algorithm may not be performed, where the performance of the ATWU valve may be assessed based on the TFT slope delta algorithm and not the ECT/TFT delta algorithm. In still other embodiments, both of the first and TFT slope delta algorithms may be performed, and the performance of the ATWU valve may be assessed based on results of both the first and TFT slope delta algorithms. For example, the performance of the ATWU valve may be assessed based on an agreement of a result of the ECT/TFT delta algorithm and a result of the TFT slope delta algorithm.

In various embodiments, a selection of either or both of the ECT/TFT delta algorithm and the TFT slope delta algorithm may be calibratable and configured prior to running the monitoring routine.

At210, method200includes determining whether conditions are met for aborting the monitoring routine. It should be appreciated that conditions for aborting the monitoring routine may occur at any time during performing the monitoring routine. For example, a condition for aborting the monitoring routine may occur during performance of the ECT/TFT delta algorithm described above at step206; a condition for aborting the monitoring routine may occur during performance of the TFT slope delta algorithm described above at step208; or at any other time during performance of the monitoring routine. If either the ECT/TFT delta algorithm or the TFT slope delta algorithm is aborted, as described in greater detail below in reference toFIGS.6,7A, and7B, the monitoring routine may be aborted. Thus, the controller may monitor the conditions for aborting the monitoring routine while the monitoring routine is running, and abort the monitoring routine when the conditions are met. The conditions for aborting the monitoring routine are described in greater detail below in reference toFIG.4.

If at210is determined that conditions are met for aborting the monitoring routine, method200proceeds to212. At212, method200includes aborting the monitoring routine, and method200ends. Alternatively, if at210it is determined that conditions are not met for aborting the monitoring routine, method200proceeds to214.

At214, at the200includes comparing completion conditions of the ECT/TFT delta algorithm and completion conditions of the TFT slope delta algorithm to determine whether the ATWU valve is stuck. The ECT/TFT delta algorithm may pass if the ECT/TFT delta algorithm completes (e.g., is not aborted) without a malfunction criteria being determined. Similarly, the TFT slope delta algorithm may pass if the TFT slope delta algorithm completes (e.g., is not aborted) without a malfunction criteria being determined.

In various embodiments, the performance of the ATWU valve may be evaluated based on at least one of a first result of the ECT/TFT delta algorithm and a second result of the TFT slope delta algorithm. The result of the ECT/TFT delta algorithm may be that the ECT/TFT delta algorithm either passes or does not pass. The result of the TFT slope delta algorithm may be that the TFT slope delta algorithm either passes or does not pass. If the ECT/TFT delta algorithm passes and the TFT slope delta algorithm complete and pass, the ATWU valve may be diagnosed as operating in accordance with expectations. If either of the ECT/TFT delta algorithm and the TFT slope delta algorithm complete and do not pass, the ATWU valve may be diagnosed as stuck. In other embodiments, the ATWU valve may be diagnosed as stuck if both of the ECT/TFT delta algorithm and the TFT slope delta algorithm complete and do not pass. In still other embodiments, one of the ECT/TFT delta algorithm and the TFT slope delta algorithm may be performed, and the performance of the ATWU valve may be assessed and a stuck ATWU valve may be diagnosed based on a completion/passage of the performed algorithm.

The ECT/TFT delta algorithm may not complete if the ECT/TFT delta algorithm is aborted for any reason. The TFT slope delta algorithm may not complete if the TFT slope delta algorithm is aborted for any reason. Because either algorithm may be aborted for a variety of reasons, an advantage of relying on two algorithms is that the stuck ATWU valve may be diagnosed even if one of the ECT/TFT delta algorithm and the TFT slope delta algorithm is aborted.

For example, the ECT/TFT delta algorithm may complete, and the TFT slope delta algorithm may not complete. If the completed ECT/TFT delta algorithm does not pass, the stuck ATWU valve may be diagnosed. Alternatively, the TFT slope delta algorithm may complete, and the ECT/TFT delta algorithm may not complete. If the completed TFT slope delta algorithm does not pass, the stuck ATWU valve may be diagnosed. If neither of the ECT/TFT delta algorithm and the TFT slope delta algorithm completes, insufficient data may be present to assess the performance of the ATWU valve. If both of the ECT/TFT delta algorithm and the TFT slope delta algorithm complete and pass, the ATWU valve may be operating as expected (e.g., not stuck).

At216, method200includes determining whether a result of either or both of the ECT/TFT delta algorithm and the TFT slope delta algorithm indicate a stuck ATWU valve. If at216it is determined that a stuck ATWU valve is indicated, method200proceeds to218. At218, method200includes setting a diagnostic flag indicating the stuck ATWU valve. Additionally, an operation of the vehicle may be adjusted, for example, to reduce an amount of degradation of components of the vehicle and/or maintain an efficiency of the vehicle. In one embodiment, an acceleration of the vehicle is limited. A malfunction indicator lamp (MIL) of the vehicle may also be illuminated, and method200ends. Alternatively, if at216it is determined that a stuck ATWU valve is not indicated, and the performance of the ATWU valve is assessed as operating in accordance with expectations, method200proceeds to220. At220, method200includes delaying until the conditions for a subsequent performance of the monitoring routine are met, and method200ends.

Turning toFIG.3, an exemplary method300is shown for determining whether entry conditions are met for performing a monitoring routine to evaluate a performance of an ATWU valve of a vehicle, such as ATWU valve22of vehicle102ofFIG.1Aand/or ATWU valve184ofFIG.1B. The monitoring routine may be the monitoring routine described above in reference to method200. The monitoring routine may be performed when a new OBD trip is initiated. If any of the entry conditions are not met, the monitoring routine may not be performed for a remainder of an OBD drive cycle. In general, the monitoring routine may be performed after a cold engine start. A cold-start of the vehicle may include an engine start after a threshold duration of time has elapsed since the engine was last turned off, for example. If the engine has been operating within the threshold duration, the engine coolant may have warmed to a temperature above a threshold temperature. For example, an engine hot start may be performed, where engine coolant temperature is above the threshold temperature at engine start, and/or where a time since a last engine start is below a preselected time. In some embodiments, the monitoring routine may be performed during a cold start event, and may not be performed during a hot start event.

Method300begins at302, where method300includes determining whether an engine of the vehicle (e.g., engine10and/or engine154) has been started. If at302it is determined that the engine has not been started, method300proceeds to304. At304, method300includes delaying until the engine is started, and method300proceeds back to302.

At305, method300includes determining whether a new onboard diagnostics (OBD) trip is being performed. If a new OBD trip is not being performed, method300proceeds to316. At316, method300includes aborting the monitoring routine, and method300ends. In other words, the monitoring routine may be performed for new OBD trips, and may not be performed multiple times within a single ODB trip. If at305is determined that a new OBD trip is being performed, method300proceeds to306.

At306, method300includes resetting parameters of the monitoring routine. Parameters indicating a status of the monitoring routine may be set to values reflecting that no results are available, no checks of entry or completion conditions have been performed, and that the monitoring routine is ready to proceed subject to the entry conditions described herein. An ECT/TFT area integral and TFT slope averages (described in greater detail below) may be reset. It should be further appreciated that the parameters may be reset at other times, for example, when the monitoring routine is aborted. For example, the parameters may be reset based on operating conditions and/or anomalies or degradations detected during performing one or more monitoring routines. The parameters may also be reset in the event of a keep alive memory (KAM) reset.

At307, method300includes measuring the ECT and an ambient air temperature (AAT) at a time of starting the engine. For example, the ECT may be monitored via an engine coolant temperature sensor (e.g. sensor26ofFIG.1A). The AAT may be measured by a temperature sensor positioned on an exterior of the vehicle (e.g. sensor58ofFIG.1A).

At308, method300includes determining whether the measured ECT and AAT are within desired temperature parameters. The desired temperature parameters may be established by threshold temperature values. For example, if the measured AAT is greater than a first AAT threshold temperature, the monitoring routine may be performed. In one embodiment, the first AAT threshold temperature is 19.4° F., where if the ambient temperature is less than 19.4° F., the conditions may not be met for running the monitoring routine. In other embodiments, method300may include determining whether the measured AAT is less than a second AAT threshold temperature, where if the AAT is greater than the second AAT threshold temperature, the conditions may not be met for running the monitoring routine.

Similarly, method300may include determining whether the measured ECT is equal to or greater than a first ECT threshold temperature, and/or determining whether the measured ECT is less than a second ECT threshold temperature, where the first ECT threshold temperature and the second ECT threshold temperature establish an ECT range within which the monitoring routine may be performed. Because the monitoring routine relies at least partly on quantifying a difference between the ECT and the TFT, if the ECT is higher than desired at engine start, there may not be enough temperature difference generated between ECT and TFT by the time the monitoring routine completes. If the ECT is lower than desired at the engine start, the difference between the ECT and the TFT may become too high due to the substantial heat transfer between engine and ECT. In one embodiment, the first ECT threshold temperature is 19.4° F., where if ECT is less than 19.4° F., the conditions may not be met for running the monitoring routine and the second ECT threshold temperature is 95° F., where if ECT is greater than 95° F., the conditions may not be met for running the monitoring routine. In some embodiments, the ECT range may depend on the measured AAT. For example, in one embodiment, if the ECT is more than 59° F. higher than the AAT at first engine start, ECT may be heated to due to an outside source such as a block heater and the conditions may not be met for running the monitoring routine.

If at308it is determined that the measured ECT and the AAT are not within the desired temperature parameters, method300proceeds to316. At316, method300includes aborting the monitoring routine. Alternatively, if at308it is determined that the ECT and the AAT are within the desired temperature parameters, method300proceeds to310.

At310, method300includes determining whether a soak time is greater than or equal to a threshold soak time. The soak time may be a time during which heat from the engine coolant radiates to various under-hood components of the vehicle (e.g., components within hood compartment103ofFIG.1A) after an engine shut-off. In other words, the monitoring routine may not be performed until the heat is allowed to dissipate for a minimum amount of time, to ensure that the various under hood components are sufficiently cooled to generate cold start conditions. In one embodiment, the threshold soak time is 6 hours, where if less than 6 hours have passed since engine-off for an internal combustion engine, the conditions may not be met for running the monitoring routine. For a hybrid vehicle, the threshold soak time may refer to an amount of continuous time during which the vehicle is not in a state of “propulsion system active”.

If at310it is determined that the soak time is not greater than or equal to the threshold soak time, method300proceeds to316, and the monitoring routine is aborted. If at310it is determined that the soak time is greater than or equal to the threshold soak time, method300proceeds to312.

At312, method300includes determining whether an output of a first timer exceeds a first threshold time. In various embodiments, the monitoring routine may not be performed if the output of the first timer does not exceed the first threshold time. The first timer may be used to ensure that a minimum duration (e.g., delay) has elapsed after the engine is started prior to running the monitoring routine, to ensure that a TFT quality factor is acceptable and to avoid initialization values coming from a transmission control module of the vehicle. In various embodiments, the minimum duration may be calibratable based on test conditions. In one embodiment, the first timer may be operated as described in reference toFIG.5.

Turning briefly toFIG.5, a method500is shown for incrementing the first timer. Method500begins at502, where method500includes determining whether an electronic control unit (ECU) of the vehicle has been switched on. The ECU of the vehicle may be included within control system14ofFIG.1A. If at502it is determined that the ECU has not been switched on, method500proceeds to504. At504, at500includes delaying until the ECU is switched on. Alternatively, if at502it is determined that the ECU has been switched on, method500proceeds to506.

At506, method500includes incrementing the first timer, and method500proceeds to508. At508, method500includes determining whether the output of the first timer exceeds the first threshold time (e.g., 20 seconds). If the output of the first timer does not exceed the first threshold time, method500proceeds back to510, where a delay is imposed until the output of the first timer exceeds the first threshold time, and method500proceeds back to508. Alternatively, if the output of the first timer exceeds the first threshold time, method500proceeds to510. At510, method500includes resetting the first timer, and method500ends.

Returning to method300, at314, method300includes determining that the conditions for performing the monitoring routine have been met, and method300ends.

Referring now toFIG.4, an exemplary method400is shown for determining whether conditions are met for aborting a monitoring routine to evaluate a performance of a ATWU valve of a vehicle, as described above in reference to method200ofFIG.2. In various embodiments, method400may be performed as part of the monitoring routine of method200described above. Method400begins at402, where method400includes determining whether an error is detected in a TFT sensor of the vehicle (e.g., TFT sensor27ofFIG.1Aand/or TFT sensor185ofFIG.1B). If an error is detected in the TFT sensor, an accurate TFT may not be generated, whereby the monitoring routine may not return an accurate result. As such, if an error is detected in the TFT sensor, method400proceeds to416. At416, method400includes aborting the monitoring routine, and method400ends.

If at402an error is not detected in the TFT sensor, method400proceeds to404. At404, method400includes determining whether an error is detected in and AAT sensor of the vehicle (e.g., external temperature sensor58ofFIG.1A). If an error is detected in the AAT sensor, an accurate AAT may not be generated, whereby the monitoring routine may not return an accurate result. As such, if an error is detected in the AAT sensor, method400proceeds to416. At416, method400includes aborting the monitoring routine, and method400ends.

If at404an error is not detected in the AAT sensor, method400proceeds to406. At406, method400includes determining whether an error is detected in an ECT sensor of the vehicle (e.g., ECT sensor26ofFIG.1Aand/or thermostat182ofFIG.1B). If an error is detected in the ECT sensor, an accurate ECT may not be generated, whereby the monitoring routine may not return an accurate result. As such, if an error is detected in the ECT sensor, method400proceeds to416. At416, method400includes aborting the monitoring routine, and method400ends.

If at406an error is not detected in the ECT sensor, method400proceeds to408. At408, method400includes determining whether an engine speed and/or an engine load is reliable. If at408an error is detected in either of an engine speed sensor and/or an engine load sensor, method400proceeds to416. At416, method400includes aborting the monitoring routine, and method400ends.

If at408the engine speed and engine load are determined to be reliable, method400proceeds to410. At410, method400includes determining whether an error is detected in an ATWU circuit of the vehicle. If an error is detected in the ATWU circuit, the monitoring routine may be able to be performed. As such, if an error is detected in the ATWU circuit, method400proceeds to416. At416, method400includes aborting the monitoring routine, and method400ends.

If at410an error is not detected in the ATWU circuit, method400proceeds to412. At412, method400includes determining whether an On Demand Self-Test routine (ODST) is running. The ODST involves checking the ATWU valve, among other sensors/actuators, for proper operation. The monitoring routine may not be performed if an On Demand test is running.

If at412it is determined that the ODST is running, the monitoring routine may not be performed, whereby method400proceeds to416. At416, method400includes aborting the monitoring routine, and method400ends. If at412it is determined that the ODST is not running, method400proceeds to414.

At414, method400includes indicating that conditions are not met for aborting the monitoring routine. The monitoring routine is therefore not aborted, and method400ends. Method400may continue to run in a loop until both the ECT/TFT delta algorithm and TFT slope delta algorithm have either completed or aborted.

Referring now toFIG.6, an exemplary method600is shown for performing a first algorithm to diagnose a stuck ATWU open valve of a vehicle, as described above in reference to the method200ofFIG.2. The first algorithm may be referred to as an ECT/TFT delta algorithm. In various embodiments, method600may be performed as part of the ATWU valve monitoring routine of method200described above. Method600is described herein as diagnosing the ATWU valve stuck in an open position, for example, when the ATWU valve is commanded closed during the initial warm up of the engine. However, method600may also be performed for diagnosing the ATWU valve stuck in a closed position, with a few modifications as described below. The ATWU valve may become stuck in the closed position when the ATWU valve is commanded to the open position to warm up the transmission fluid during a cold start of an engine after ECT has exceeded the functional threshold. In other words, method600may be used to diagnose both the ATWU valve being stuck in the open position and the ATWU valve being stuck in the closed position, during operation of the vehicle during a single OBD trip.

Method600begins at602, where method600includes determining whether an engine of the vehicle is running. The ECT/TFT delta algorithm may rely on the engine being continuously running for an amount of time, where if a cumulative amount of time during which the engine is stopped is greater than a threshold time, the ECT/TFT delta algorithm may be aborted.

If at602it is determined that the engine is not running, method600proceeds to604. At604, method600includes incrementing a second timer, where the second timer counts a cumulative amount time the engine has not been running while the method600is being performed, and method600proceeds to608. At608, method600includes determining whether an output of the second timer exceeds a second threshold time. In various embodiments, the second threshold time, and the other thresholds described in method600and in other methods of this disclosure, may be calibratable, where the thresholds are established during a system calibration and may be set between predetermined upper and lower bounds. For example, the second threshold can be set to 100 seconds. If the second timer counts to more than 100 seconds, the method600may not be performed.

If at608it is determined that the output of the second timer does not exceed the second threshold time, method600returns to602. If at608it is determined that the output of the second timer exceeds the second threshold time, method600proceeds to610. At610, method600includes aborting the ECT/TFT delta algorithm, and method600ends.

If at602it is determined that the engine is running, then method600proceeds to606. At606, method600includes calculating a no heat ratio (NO HR). The no heat ratio is the ratio of a time the engine is running below an engine speed threshold or engine load threshold to a total time engine has been running while method600is being performed. These thresholds may be calibratable. At612, method600includes determining whether the NO HR is less than a NO HR threshold. If at612it is determined that the NO HR is not less than the NO HR threshold, method600proceeds to618. Alternatively, if at612it is determined that the NO HR exceeds the NO HR threshold, method600proceeds to614. At614, method600includes incrementing a third timer. At616, method600includes determining whether an output of the third timer exceeds a third threshold time. If at616it is determined that the output of the third timer exceeds the third threshold time, method600proceeds to610, and the ECT/TFT delta algorithm is aborted. Alternatively, if at616it is determined that the output of the third timer does not exceed the third threshold time, method600proceeds to618.

In other words, the NO HR is calculated while the algorithm is running, and a cumulative amount of time that the NO HR is less than the NO HR threshold is computed. If the cumulative amount of time that the NO HR is less than the NO HR threshold exceeds the third threshold time, the algorithm is not continued.

At618, method600includes calculating a torque slip of the engine, based on the engine speed and a speed of a turbine of a torque converter of the vehicle (e.g., turbine shaft158of torque converter157ofFIG.1B). Specifically, the torque slip may be calculated based on equation 1 below:

At620, method600includes determining whether the torque slip exceeds a torque slip threshold. If at620it is determined that the torque slip does not exceed the torque slip threshold, method600proceeds to626. Alternatively, if at620it is determined that the torque slip exceeds the torque slip threshold, method600proceeds to622. At622, method600includes incrementing a fourth timer. At624, method600includes determining whether an output of the fourth timer is greater than a fourth threshold time. If at624it is determined that the output of the fourth timer is greater than the fourth threshold time, method600proceeds to610, and the ECT/TFT delta algorithm is aborted. Alternatively, if at624it is determined that the output of the fourth timer does not exceed the fourth threshold time, method600proceeds to626.

In other words, a cumulative amount of time that the torque slip is greater than the torque slip threshold is computed. If the cumulative amount of time that the torque slip is greater than the torque slip threshold exceeds the fourth threshold time, the algorithm is not continued.

At626, method600includes determining whether the ATWU valve is in a closed position (e.g., commanded to the closed position and/or expected to be in the closed position). If at626the ATWU valve is in the closed position, method600proceeds to632. Alternatively, if at626the ATWU valve is not in the closed position (e.g., the ATWU valve is open), method600proceeds to628. At628, method600includes incrementing a fifth timer. At630, method600includes determining whether an output of the fifth timer exceeds a fifth threshold time. If at630it is determined that the output of the fifth timer exceeds the fifth threshold time, method600proceeds to610, and the ECT/TFT delta algorithm is aborted. Alternatively, if at630it is determined that the output of the fifth timer does not exceed the fifth threshold time, method600proceeds to632. In other words, a cumulative amount of time that the ATWU is open is computed. If the cumulative amount of time that the ATWU is open exceeds the fifth threshold time, the algorithm is not continued.

At632, method600includes determining whether a temperature of an engine coolant (ECT) exceeds a functional threshold. The functional threshold is dictated by a controller (e.g., controller12) and may be the temperature at which the ATWU is commanded to an open position (e.g., 70° C.). The ECT may be measured by an ECT sensor disposed on an engine coolant loop of the vehicle, such as ECT sensor26described above in relation toFIG.1A. If at632it is determined that the ECT is less than the functional threshold, method600proceeds to636.

At636, method600includes determining whether a difference between the ECT and the TFT is greater than a predetermined temperature threshold. The TFT may be monitored by a TFT sensor (e.g. TFT sensor27). If at636it is determined that a difference between the ECT and the TFT is not greater than the threshold value, method600proceeds back to602. If at636it is determined that the difference between the ECT and the TFT is greater than the temperature threshold, method600proceeds to638.

At638, method600includes updating an area integral calculation. The area integral calculation is updated in a first step by subtracting the threshold value from the calculated difference between the ECT and the TFT, and multiplying the result by a time of a regular interval between each computation of method600. In a second step, the area integral is then incremented by the result of the first step. After the area integral calculation is updated, method600proceeds back to602.

In other words, the difference between the ECT and the TFT is determined at each iteration of the ECT/TFT delta algorithm (e.g., at regular intervals of time). A cumulative area integral between the ECT and the TFT may then be computed each regular interval (e.g., a second) whenever the difference between the ECT and the TFT is greater than the threshold. When the difference between the ECT and the TFT decreases below the threshold, the area integral is frozen, and the ECT/TFT delta algorithm continues. Thus, the area between the ECT and TFT curves above the temperature threshold may be computed, and the area between the ECT and TFT curves below the temperature threshold may not be computed. If any of the above conditions for aborting the ECT/TFT delta algorithm occur prior to ECT exceeding the functional threshold, the ECT/TFT delta algorithm is not continued.

Returning to632, if at632it is determined that the ECT is not less than the functional threshold, method600proceeds to634. At634, method600includes determining whether the output of the third timer exceeds a sixth threshold time.

If at634it is determined that the output of the third timer exceeds the sixth threshold time, method600proceeds to610, and the ECT/TFT delta algorithm is aborted. Alternatively, if at634it is determined that the output of the third timer does not exceed the sixth threshold time, method600proceeds to640. In other words, if the total time the engine has been running since the start of new OBD trip with no abort conditions satisfied is less than a minimum amount of time, the ECT/TFT delta algorithm is aborted.

At640, method600includes determining whether a result of dividing the area integral by a run time of the ECT/TFT delta algorithm is greater than a threshold value. The run time may be an amount of time passed since an initiation of the ECT/TFT delta algorithm at602. By dividing the calculated area integral by the run time of the first algorithm, an average temperature difference between the ECT and the TFT is determined for a regular interval.

If at640it is determined that the result of dividing the area integral by the run time of the ECT/TFT delta algorithm is not greater than the threshold value (e.g., is less than or equal to the threshold value) method600proceeds to642. At642, method600includes indicating that the ECT/TFT delta algorithm does not pass, and method600ends. Alternatively, if at640it is determined that the result of dividing the area integral by the run time of the ECT/TFT delta algorithm is greater than the threshold value, method600proceeds to644. At644method600includes indicating that the ECT/TFT delta algorithm passes, and method600ends. If the algorithm does not pass, the ATWU valve may be indicated as stuck in the open position.

Thus, the ECT/TFT delta algorithm includes a series of iterations that are performed over time, where during each iteration, a series of conditions for continuing the ECT/TFT delta algorithm are verified. The verification may involve comparing an output of one or more sensors and/or a result of a calculation to a predetermined threshold valve. If a condition for continuing is verified, the ECT/TFT delta algorithm proceeds to a subsequent condition. If a condition for continuing is not verified, a timer corresponding to the condition is incremented. During each subsequent iteration, an output of each timer may be compared with a corresponding timer threshold. Each timer may have a different threshold. If a timer threshold is exceeded, the ECT/TFT delta algorithm is aborted and does not complete. During each iteration, the ECT is compared with the TFT. If the ATWU valve is in an open or partially open position, heat may be transferred from the engine coolant to the transmission fluid, whereby a difference between the ECT and the TFT may be smaller. If the ATWU valve is in a closed position, heat may not be transferred from the engine coolant to the transmission fluid, whereby a difference between the ECT and the TFT may be greater. Thus, the area integral calculated between the ECT and the TFT may be used to indicate a stuck ATWU valve.

In an alternate scenario, method600may also be used to diagnose an ATWU valve stuck in a closed position, for example, when the ATWU valve is commanded to an open position to warm up the transmission fluid during a cold start. When method600is performed to diagnose the ATWU valve stuck in the closed position, steps602-624are the same as described above.

At626, method600includes determining whether the ATWU valve is in an open position (e.g., commanded to the open position and/or expected to be in the open position). If at626the ATWU valve is in the open position, method600proceeds to634. Alternatively, if at626the ATWU valve is not in the open position (e.g., the ATWU valve is open), method600proceeds to628and630, as described above.

In the alternate scenario, step632is skipped, as the ATWU is already commanded open, and the method proceeds to634. At634, method600includes determining whether the ECT exceeds the operating temperature minus an offset threshold. The operating temperature is a temperature at which the coolant and transmission fluid would remain for a remainder of the drive cycle in the absence of any abnormal driving condition. If at634it is determined that the ECT exceeds the operating temperature minus the offset threshold, method600proceeds to640. Alternatively, if at634it is determined that ECT does not exceed the operating temperature minus an offset threshold, method600proceeds to636.

At636in the alternate scenario, method600includes determining whether a difference between the ECT and the TFT is greater than a second predetermined temperature threshold. If at636it is determined that a difference between the ECT and the TFT is not greater than the threshold value, method600proceeds back to602. If at636it is determined that the difference between the ECT and the TFT is greater than the temperature threshold, method600proceeds to638, and the area integral is updated as described above.

At640in the alternate scenario, method600includes determining whether a result of dividing the area integral by a run time of the ECT/TFT delta algorithm is less than a threshold value. If at640it is determined that the result of dividing the area integral by the run time of the ECT/TFT delta algorithm is not less than the threshold value (e.g., is greater than or equal to the threshold value) method600proceeds to644. At644, method600includes indicating that the ECT/TFT delta algorithm passes, and method600ends. Alternatively, if at640it is determined that the result of dividing the area integral by the run time of the ECT/TFT delta algorithm is less than the threshold value, method600proceeds to642. At642, method600includes indicating that the ECT/TFT delta algorithm does not pass, and method600ends. If the algorithm does not pass in the alternate scenario, the ATWU valve may be indicated as stuck in the closed position.

Referring now toFIG.7A, a first part of an exemplary method700is shown for performing a second algorithm to diagnose a stuck ATWU valve of a vehicle, also as described above in reference to method200ofFIG.2. The second algorithm may be referred to as the TFT slope delta algorithm. A second part of method700is shown inFIG.7B, described below. In various embodiments, method700may be performed as part of the monitoring routine of method200described above. For example, the monitoring routine of method200may determine whether the ATWU valve is stuck by comparing a result of method700with a result of method600ofFIG.6. In other embodiments, the monitoring routine of method200may determine whether the ATWU valve is stuck based on either a result of method700or a result of method600ofFIG.6. If either of the ECT/TFT delta algorithm or the TFT slope delta algorithm is aborted, or does not pass, the monitoring routine of method200may be aborted. Both methods600and700rely on measurements of an ECT of the vehicle, and a TFT of the vehicle. In particular, method700relies on comparing a first slope of the TFT for sample temperatures when the ATWU valve is closed (referred to herein as closed sample) with a second slope of the TFT for sample temperatures when the ATWU valve is open (referred to herein as open sample). As with method600, method700may be performed over various iterations, where during each iteration, a TFT is measured and a slope (either from a closed sample or an open sample) is calculated using a linear regression method.

Method700is described herein as diagnosing the ATWU valve stuck in either a closed or an open position, for example, when the ATWU valve is commanded to the open position to warm up the transmission fluid during a cold start of an engine of the vehicle after ECT reaches the functional threshold. The ATWU valve may become stuck in the open position when the ATWU valve is commanded closed during the initial warm up of the engine.

Method700begins at702, where method700includes determining whether the ECT is greater than a functional threshold minus a calibratable offset threshold. As described above in reference to method600, the functional threshold is dictated by a controller (e.g., controller12) and is the temperature at which the ATWU is commanded to an open position (e.g., 70° C.). For example, the ATWU may be closed at an engine start event (e.g., a cold start), and the ATWU valve may be opened when the engine coolant is warm enough to provide heat to a transmission of the vehicle (e.g., transmission40). The ECT may be measured by an ECT sensor disposed on an engine coolant loop of the vehicle, such as ECT sensor26described above in relation toFIG.1A. Method700is planned to start its closed slope calculation at a certain offset below the functional threshold. If at702it is determined that the ECT is not greater than the functional threshold minus the calibratable offset threshold, method700proceeds to704.

At704, method700includes resetting parameters for an average TFT slope to 0 for both open samples and closed samples (e.g., for conditions where the ATWU valve is open and closed, respectively). Method700proceeds back to702.

If at702it is determined that the ECT is greater than the functional threshold minus the calibratable offset threshold, method700proceeds to706. At706, method700includes determining whether the ATWU valve is in a closed position. If at706it is determined that the ATWU valve is in the closed position, a closed sample TFT is collected, and method700proceeds to710.

At710, method700includes determining whether the closed sample TFT count is greater than a first threshold sample count. The TFT slope delta algorithm may rely on a minimum number of sample TFTs for a robust calculation of the TFT slope. If at710it is determined that the closed sample TFT count is greater than the first threshold sample count, method700proceeds to712. At712, method700includes aborting the TFT slope delta algorithm, and method700ends. Alternatively, if at710it is determined that the closed sample TFT count is not greater than the first threshold sample count (e.g., less than or equal to the first threshold sample count), method700proceeds to714.

At714, method700includes calculating parameters for a linear regressive TFT slope for the closed samples. In other words, an average rate of change of closed sample TFT measurements prior to commanding the ATWU valve open is calculated. The TFT slope may be calculated by performing a linear regression of the closed sample TFT measurements, in accordance with equation 2 described below:

b=n⁡(∑xy)-(∑x)⁢(∑y)n⁡(∑x2)-(∑x)22where b is the average rate of change of the TFT slope, x is a sample count, and y is a TFT measurement.

At716, method700includes calculating an average engine speed and an average engine load for the closed sample TFT. The average engine speed and average engine load may be calculated over a period of time during which the closed sample TFTs are collected. The average engine speed and average engine load may be calculated with every iteration (e.g., for example, every second).

At718, the closed sample TFT is incremented to obtain a new closed sample TFT, and method700proceeds back to702.

In this way, during the time that the ATWU valve is closed, TFT samples are collected, and a slope of the TFT samples is calculated using a linear regression. When the ATWU valve is opened, the TFT slope for the closed samples is frozen for remaining steps of the TFT slope delta algorithm.

Returning to706, if at706it is determined that the ATWU valve is not in the closed position (e.g., the ATWU valve is open), method700proceeds to708. At708, method700includes determining whether the closed sample TFT count is less than a second threshold sample count.

If at708it is determined that the closed sample TFT is less than the second threshold sample count, method700proceeds to712. At712method700includes aborting the TFT slope delta algorithm, and method700ends.

Alternatively, if at708it is determined that the closed sample TFT is not less than the second threshold temperature (e.g., the closed sample TFT is greater than or equal to the second threshold temperature), method700proceeds to720. At720, method700includes performing a final calculation and freezing the linear regressive closed sample TFT slope (e.g., reflecting the rate of change of the slope), and method700proceeds to722. At722, method700includes incrementing a delay timer, and method700proceeds to724.

At724, method700includes determining whether an output of the delay timer is greater than a seventh threshold time. If at724it is determined that the output of the delay timer is not greater than the seventh threshold time, method700proceeds back to722. Alternatively, if at724it is determined that the output of the delay timer is greater than the seventh threshold time, method700proceeds to730ofFIG.7B, where the TFT slope delta algorithm continues. The delay timer is employed to allow the heat transfer between ECT and transmission fluid within a heat exchanger, such as heat exchanger180inFIG.1B, and subsequently transfer the heat to a conduit such as transmission coolant loop165inFIG.1Bas seen by TFT sensor.

At730, method700includes determining whether the engine is running. If at730it is determined that the engine is not running, method700proceeds to732. At732, method700includes aborting the TFT slope delta algorithm, and method700ends. Alternatively, if at730it is determined that the engine is running, method700proceeds to734.

At734, method700includes determining whether the ATWU valve is in an open position (e.g., commanded to the open position and/or expected to be in the open position). For example, the ATWU valve may be commanded to the open position to direct engine coolant to a heat exchanger (e.g., heat exchanger180ofFIG.1B) where heat from the engine coolant may be transferred to transmission fluid circulating through a transmission of the vehicle.

If at734it is determined that the ATWU valve is not in the open position, method700proceeds to732, and the TFT slope delta algorithm is aborted. If at734it is determined that the ATWU valve is in the open position, method700proceeds to736.

At736, method700includes calculating parameters for a linear regressive open sample TFT slope. An average rate of change of the TFT slope for the open samples (e.g., after the ATWU valve is commanded open) is calculated, by performing a linear regression of the open sample TFT measurements, in accordance with equation 2 described above in reference to step714.

At738, method700includes calculating an average engine speed and an average engine load for the open sample TFT.

At740, the open sample TFT is incremented, to obtain a new open sample TFT, and method700proceeds to742.

At742, method700includes determining whether the number of open sample TFTs is less than a third threshold count. In some embodiments, the third threshold count may be equal to the the second threshold count described above in reference to step708.

If at742it is determined that the number of open sample TFTs is less than the third threshold count, method700proceeds back to730. Alternatively, if at742it is determined that the number of open sample TFTs is not less than the third threshold count (e.g., the number of open samples is greater than or equal to the third threshold count), method700proceeds to744.

At744, method700includes calculating a difference between a first average engine speed when the ATWU valve is open, and a second average engine speed when the ATWU valve is closed. In various environments, the average engine speed may be determined based on an output of an engine speed sensor of the vehicle. The first average engine speed may be determined over a duration during which the number of open sample TFTs were measured, and the second average engine speed may be determined over a duration during which the number of closed sample TFTs were measured. Method700proceeds to746.

At746, method700includes determining whether the difference between the first average engine speed when the ATWU valve is open and the second average engine speed when the ATWU valve is closed is greater than a threshold speed value. If at746it is determined that the difference exceeds the threshold speed value, method700proceeds to732, and the TFT slope delta algorithm is aborted. Alternatively, if at746is determined that the difference does not exceed the threshold speed value, method700proceeds to748.

At748, method700includes calculating a difference between a first average engine load when the ATWU valve is open and a second average engine load when the ATWU valve is closed. The first average engine load may be determined over a duration during which the number of open sample TFTs were measured, and the second average engine load may be determined over a duration during which the number of closed sample TFTs were measured. Method700proceeds to750.

At750, method700includes determining whether the difference between the first average engine load when the ATWU valve is open and the second average engine load when the ATWU valve is commanded closed is greater than a threshold load value. If at750it is determined that the difference exceeds the threshold load value, method700proceeds to732, and the TFT slope delta algorithm is aborted. Alternatively, if at750is determined that the difference does not exceed the threshold load value, method700proceeds to752.

At752, method700includes calculating a TFT slope delta, where the TFT slope delta is a difference between the average rate of change of the TFT for sample TFTs when the ATWU valve is open, and the average rate of change of the TFT for sample TFTs when the ATWU valve is closed. Specifically, the TFT slope delta is calculated as a difference between the TFT linear regressive slope for the open samples and the TFT linear regressive slope for the closed samples. Method700proceeds to754.

At754, method700includes determining whether the TFT slope delta is greater than a threshold value. If at754it is determined that the change in the TFT slope delta is greater than the threshold value, method700proceeds to756. At756, method700includes indicating that the TFT slope delta algorithm passes, and method700ends.

Alternatively, if at754it is determined that the TFT slope delta is not greater than the threshold change, method700proceeds to758. At758, method700includes indicating that the TFT slope delta algorithm does not pass, and method700ends.

Thus, in accordance with the TFT slope delta algorithm, a first slope of TFT measurements taken in a first condition in which the ATWU valve is closed is calculated, and a second slope of TFT measurements taken in a second condition in which the ATWU valve is open is calculated. If an engine speed or engine load difference between the open samples and the closed samples exceeds a threshold, the TFT slope delta algorithm is aborted. The first slope is compared with the second slope. If the difference between the first slope and the second slope is large (e.g., above a first threshold), it may be inferred that engine coolant is circulating through a transmission heat exchanger of the vehicle and heating the transmission fluid, whereby the ATWU valve is open (as expected). Alternatively, if the difference between the first slope and the second slope is small (e.g., below a second threshold), it may be inferred that the transmission fluid is not absorbing heat at an expected rate. Therefore, the engine coolant may not be circulating through the transmission heat exchanger, and it may be inferred that the ATWU valve is closed (not as expected). Under such conditions, the TFT slope delta algorithm does not pass, and a stuck ATWU valve may be indicated.

In an alternate scenario, method700may also be used to diagnose an ATWU valve stuck in an open position. When method700is performed to diagnose the ATWU valve stuck in the open position, the method may be the same as described above, since the method700uses a difference in rate of change of TFT before and after the valve changes state. The heat transfer to transmission will occur from the time the valve is stuck open, and there will be no change in the TFT slope before and after the ATWU valve is commanded open. The TFT slope delta is calculated as described above, and compared to a second threshold change, which may be different from the threshold change of the scenario described above. In the alternate scenario, if the TFT slope delta is less than the second threshold change, the algorithm may not pass, and if the TFT slope delta is greater than the second threshold change, the algorithm may pass. If the algorithm does not pass, the ATWU valve may be indicated as stuck in the open position.

Turning now toFIG.8A, an example timing diagram800is shown for monitoring an ATWU valve of a cooling system of a vehicle, according to the method depicted inFIG.2, and as applied to the system described herein and with reference toFIGS.1A and1B. Instructions for performing the actions described in timing diagram800may be executed by a controller (e.g., the controller12ofFIG.1A) based on instructions stored on a memory of the controller and in conjunction with signals received from sensors of the vehicle and cooling system, such as the sensors described above in relation to vehicle102ofFIG.1A.

Timing diagram800shows plots802,804,808, and810, which illustrate states of the ATWU valve and temperature measurements/calculations of engine coolant and transmission fluid with respect to time (horizontal axis), with time points of interest illustrated by vertical dashed lines. Plot802indicates an ECT of the vehicle, in accordance with a temperature range depicted on a y axis from 0° C. to 70° C. A dotted line801indicates a threshold temperature (70° C.) at which the ATWU valve may be actuated. Plot804indicates a TFT of the vehicle, in accordance with a temperature range depicted on a y axis from 0° C. to 70° C. Plot808indicates a rate of change (e.g., slope) of the TFT depicted in plot804for each TFT sample point, from a baseline of 0 indicated on the y axis. Plot810indicates a state of the ATWU valve, where the state may be OPEN or CLOSED.

At time t0, an engine of the vehicle is turned on in a cold start event, and a new OBD trip is initiated. An ATWU valve monitoring routine (e.g., method200) is initiated, and various parameters used by the monitoring are initialized and/or reset. A precondition for starting the new OBD trip may be that a minimum duration has passed without the engine being on and/or the vehicle being operated. At time t0, the ECT and the TFT are both at an ambient temperature (e.g., close to 0° C.). The ATWU valve is in a closed position, where an engine coolant loop does not circulate coolant through a transmission of the vehicle.

Between time t0 and time t1, the engine coolant begins to circulate throughout the engine coolant loop, and the ECT increases as a result of heat generated by the engine, as shown by plot802. The TFT increases at a slower rate than the ECT, as no heat from the engine coolant is transferred to the transmission fluid. Because of the slower rate of increase of the TFT with respect to the ECT, the difference between the ECT and the TFT increases. The slope of the TFT remains gradual, as shown by plot808.

At time t1, the ECT reaches the threshold temperature indicated by line801, and the ATWU valve is commanded to an open position, as indicated by plot810. The normalized area integral of the difference between the ECT and the TFT may be used by a first algorithm of the ATWU monitoring routine (e.g., the ECT/TFT delta algorithm ofFIG.6) to determine whether the ATWU valve may be stuck. The ECT/TFT algorithm may determine that a cumulative difference between ECT and the TFT indicated by shaded area806(e.g., between time the closing of the ATWU valve at t0 and the opening of the ATWU valve at t1) is greater than a threshold difference, from which it may be inferred that the ATWU valve was not stuck in open position between t0 and t1 position, whereby an ECT/TFT delta algorithm may pass.

Between time t1 and time t2, heated engine coolant begins to circulate through the ATWU valve to a transmission heat exchanger (e.g. heat exchanger180ofFIG.1B), and heat from the engine coolant begins to be transferred to the transmission fluid, thereby increasing the TFT. The rate of increase of the TFT may be rapid, as indicated by the increase in the TFT slope shown by plot808. As the TFT increases, the difference between the ECT and the TFT decreases.

At time t2, the TFT approaches the ECT. Specifically, the decrease in the difference between the ECT and the TFT between time t1 and time t2 may be an indication that heat is being exchanged between the engine coolant and the transmission fluid as expected, from which it may be inferred that the ATWU valve is in the open position. The slope of the TFT is close to maximum as the TFT reaches a maximum temperature.

Between time t2 and time t3, the rise in ECT temperature may be similar to TFT, as both rise close to their operating temperatures. The operating temperature is the temperature at which the coolant and transmission fluid would remain for a remainder of the drive cycle in the absence of any abnormal driving condition. The difference between ECT and the TFT decreases towards zero.

A difference in the TFT slope between conditions in which the ATWU valve is open and the ATWU valve is closed (at a calibratable time before and after t1) may be used by a second algorithm of the ATWU monitoring routine (e.g., the TFT slope delta algorithm ofFIGS.7A and7B) to determine whether the ATWU valve may be stuck. The TFT slope delta algorithm may compare a first TFT slope just prior to t1 with a second TFT slope just after t1. If the second slope is greater than the first slope by a threshold amount, it may be inferred that the ATWU valve is in the open position (e.g., not stuck in the closed position), and the TFT slope delta algorithm may pass.

At time t3, the ECT reaches a target temperature close to operating temperature as described above. As a result of either or both of the TFT slope delta algorithm and the ECT/TFT delta algorithm passing, the ATWU monitoring routine may indicate that the ATWU valve is open.

In contrast,FIG.8Bshows an example timing diagram850for monitoring the ATWU valve according to the method depicted inFIG.2, where the ATWU valve becomes stuck. Timing diagram850includes plots852,854,858, and860, which illustrate states of the ATWU valve and temperature measurements/calculations of engine coolant and transmission fluid with respect to time (horizontal axis), similar to plots802,804,808, and810ofFIG.8A. Plot852indicates an ECT of the vehicle, in accordance with a temperature range depicted on a y axis from 0° C. to 70° C. Dotted line801indicates a threshold temperature (70° C.) at which the ATWU valve may be actuated. Plot854indicates a TFT of the vehicle, in accordance with a temperature range depicted on a y axis from 0° C. to 70° C. Plot858indicates a rate of change (e.g., slope) of the TFT depicted in plot854for each TFT sample point, from a baseline of 0 indicated on the y axis. Plot860indicates a state of the ATWU valve, where the state may be OPEN or CLOSED.

At time t0, the engine is turned on in a cold start event, and a new OBD trip is initiated. The ATWU valve monitoring routine (e.g., method200) is initiated, and various parameters used by the monitoring are initialized and/or reset. At time t0, the ECT and the TFT are both at an ambient temperature (e.g., close to 0° C.). The ATWU valve is expected to be in a closed position, where an engine coolant loop does not circulate coolant through a transmission of the vehicle, but is stuck in the open position.

Between time t0 and time t1, the engine coolant begins to circulate throughout the engine coolant loop, and the ECT increases as a result of heat generated by the engine, as shown by plot852. The TFT increases at a rate closer to the ECT, as heat from the engine coolant is transferred to the transmission fluid. Because of the similar rate of increase of the TFT with respect to the ECT, the difference between the ECT and the TFT remains relatively constant. The slope of the TFT remains gradual (as there is no large difference between the ECT and TFT temperature from the engine start), as shown by plot858.

As in timing diagram800ofFIG.8A, at time t1, the ECT reaches the threshold temperature indicated by line801, and the ATWU valve is commanded to an open position, as indicated by plot860. However, inFIG.8B, the ATWU valve is stuck in the open position, as shown by plot860. The normalized area integral of the difference between the ECT and the TFT may be used by a first algorithm of the ATWU monitoring routine (e.g., the ECT/TFT delta algorithm ofFIG.6) to determine whether the ATWU valve may be stuck. Since the ECT and TFT rise at relatively the same rate, the normalized area integral between the ECT and TFT is small. The ECT/TFT delta algorithm may determine that a cumulative difference between ECT and the TFT indicated by shaded area856, between a time the closing of the ATWU valve at t0 and the opening of the ATWU valve at t1, does not exceed a threshold difference, from which it may be inferred that ATWU valve was stuck in open position between t0 and t1 position, whereby an ECT/TFT delta algorithm may not pass.

As such, between time t1 and time t2, in contrast toFIG.8A, there is no large difference between ECT and TFT (as the ATWU valve is open from engine start) and no additional heat from the engine coolant is transferred to the transmission fluid. Thus, the TFT increases gradually in plot854, as indicated by the slow increase in the TFT slope shown by plot858.

At time t2, the slope of the TFT reaches remains relatively constant as there is no sudden heat transfer from the ECT.

A difference in the TFT slope between conditions in which the ATWU valve is closed and the ATWU valve is opened may be used by a second algorithm of the ATWU monitoring routine (e.g., the TFT slope delta algorithm ofFIGS.7A and7B) to determine whether the ATWU valve may be stuck. The TFT slope delta algorithm may compare a first TFT slope just prior to t1 with a second TFT slope just after t1. As shown by plot858, the difference between the first slope and the second slope is small (e.g., less than a threshold amount), whereby may be inferred that the ATWU valve is not in the closed position (e.g., stuck in the open position), and the TFT slope delta algorithm may not pass.

Between time t2 and time t3, the slope of the ECT and TFT may decrease as heat is transferred from the engine coolant to the radiator. The difference between ECT and the TFT decreases towards zero, and the TFT slope decreases towards zero.

At time t3, the ECT reaches a target temperature close to operating temperature, as described above in reference toFIG.8A. As a result of either or both of the TFT slope delta algorithm and the ECT/TFT delta algorithm not passing, the ATWU monitoring routine may indicate that the ATWU valve is stuck in the open position.

Thus, a robust ATWU valve monitoring routine is described, based on two algorithms. The two algorithms include an ECT/TFT delta algorithm, which measures a normalized difference in temperature between the ECT and the TFT when the ATWU valve is closed, and a TFT slope delta algorithm, which compares a first rate of change of TFT measurements prior to commanding the ATWU valve open with a second rate of change of TFT measurements after commanding the ATWU valve open. A stuck ATWU valve may be indicated by either of the two algorithms, or by comparing results of the two algorithms. In this way, a stuck ATWU valve may be more rapidly and accurately diagnosed than by other diagnostic methods, or by a single diagnostic method. As a result of relying on two different algorithms, the stuck ATWU valve may be diagnosed even if a result cannot be generated by one of the algorithms. The technical effect of using the robust ATWU valve monitoring routine including the two algorithms is that a more robust diagnosis of a stuck ATWU valve may be made.

The disclosure also provides support for a method for an active Transmission Warmup (ATWU) valve monitoring routine of a vehicle, the method comprising: determining a temperature difference between an engine coolant temperature (ECT) and a transmission fluid temperature (TFT) over a duration before the ATWU valve is commanded from a closed position to an open position or from the open position to the closed position, comparing a rate of change of the TFT before and after the ATWU valve is commanded to the open position or the closed position, and indicating a stuck ATWU valve based on at least one of the temperature difference, the TFT rate of change comparison, or a combination thereof, based on a calibration parameter. In a first example of the method, the ATWU valve monitoring routine is performed during an engine cold start. In a second example of the method, optionally including the first example, the method further comprises: initiating the ATWU valve monitoring routine in response to all of: a measured ambient air temperature (AAT) being below a threshold AAT temperature, the ECT being greater than a threshold ECT temperature, a soak time of the vehicle being greater than or equal to a threshold soak time, and a time during which an engine of the vehicle is on being greater than a first threshold time. In a third example of the method, optionally including one or both of the first and second examples, the method further comprises: indicating the stuck ATWU valve based on both of the temperature difference and the TFT rate of change comparison. In a fourth example of the method, optionally including one or more or each of the first through third examples, the method further comprises: indicating the stuck ATWU valve based on one of the temperature difference and the TFT rate of change comparison. In a fifth example of the method, optionally including one or more or each of the first through fourth examples, indicating the stuck ATWU valve based on the temperature difference between the ECT and the TFT over the duration before the ATWU valve is commanded from the closed position to the open position further comprises: calculating a difference between the ECT and the TFT at a plurality of regular intervals, at each regular interval of the plurality of regular intervals: in response to the temperature difference being greater than a threshold temperature difference, updating a cumulative calculated area integral between the ECT and the TFT, and in response to the temperature difference decreasing below the threshold temperature difference: dividing the calculated area integral by a time elapsed since the ATWU valve is commanded closed to determine an average temperature difference between the ECT and the TFT for a regular interval, in response to the average temperature difference being greater than a threshold average temperature difference, not indicating the stuck ATWU valve, and in response to the average temperature difference not being greater than the threshold average temperature difference, indicating that the ATWU valve is stuck in the open position. In a sixth example of the method, optionally including one or more or each of the first through fifth examples, indicating the stuck ATWU valve based on the temperature difference between the ECT and the TFT over the duration before the ATWU valve is commanded from the open position to the closed position further comprises: calculating a difference between the ECT and the TFT at a plurality of regular intervals, at each regular interval of the plurality of regular intervals: in response to the temperature difference being greater than a threshold temperature difference, updating a cumulative calculated area integral between the ECT and the TFT, and in response to the temperature difference decreasing below the threshold temperature difference: dividing the calculated area integral by a time elapsed since the ATWU valve is commanded open to determine an average temperature difference between the ECT and the TFT for a regular interval, in response to the average temperature difference being less than a threshold average temperature difference, not indicating the stuck ATWU valve, and in response to the average temperature difference not being less than the threshold average temperature difference, indicating that the ATWU valve is stuck in the closed position. In a seventh example of the method, optionally including one or more or each of the first through sixth examples, indicating the stuck ATWU valve based on comparing the rate of change of the TFT before and after the ATWU valve is commanded from the closed position to the open position further comprises: collecting a first minimum number of sample TFT measurements at regular intervals prior to opening the ATWU valve, performing a first linear regression to calculate a first TFT slope of the first minimum number of sample TFT measurements, collecting a second minimum number of sample TFT measurements at regular intervals after opening the ATWU valve, performing a second linear regression to calculate a second TFT slope of the second minimum number of sample TFT measurements, calculating a difference between the first TFT slope and the second TFT slope, in response to the difference being greater than a threshold difference, not indicating the stuck ATWU valve, and in response to the difference not being greater than the threshold difference, indicating that the ATWU valve is stuck in the closed position. In a eighth example of the method, optionally including one or more or each of the first through seventh examples, the method further comprises: in response to the stuck ATWU valve being indicated, limiting an acceleration of the vehicle. In a ninth example of the method, optionally including one or more or each of the first through eighth examples, the method further comprises: aborting the ATWU valve monitoring routine in response to at least one of the following: an error being detected in a TFT sensor of the vehicle, an error being detected in an ECT sensor of the vehicle, an error being detected in an AAT sensor of the vehicle, an error being detected in an engine speed sensor of the vehicle, an error being detected in an engine load sensor of the vehicle, and an error being detected in an ATWU circuit of the vehicle.

The disclosure also provides support for a system for a vehicle, comprising: a coolant system configured to circulate coolant through at least an engine, a radiator, a heater core, a controller, storing instructions in non-transitory memory that, when executed, cause the controller to: during a cold start of the engine, perform a monitoring routine that monitors a status of an active Transmission Warmup (ATWU) valve of the coolant system that when commanded open, allows the coolant to circulate through a transmission heat exchanger of the vehicle, the monitoring routine comprising: determining a temperature difference between an engine coolant temperature (ECT) and a transmission fluid temperature (TFT) over a duration before the ATWU valve is commanded from an open position to a closed position or from the closed position to the open position, comparing a rate of change of the TFT before and after the ATWU valve is commanded from the open position to the closed position or from the closed position to the open position, indicating a stuck ATWU valve based on at least one of the temperature difference, the TFT rate of change comparison, or a combination thereof, based on a calibration parameter. In a first example of the system, further instructions are stored in the non-transitory memory that when executed, cause the controller to indicate a stuck ATWU valve based on one of the temperature difference and the TFT rate of change comparison. In a second example of the system, optionally including the first example, further instructions are stored in the non-transitory memory that when executed, cause the controller to indicate a stuck ATWU valve based on both of the temperature difference and the TFT rate of change comparison. In a third example of the system, optionally including one or both of the first and second examples, the monitoring routine is initiated in response to all of: a measured ambient air temperature (AAT) being below a threshold AAT temperature, the ECT being greater than a threshold ECT temperature, a soak time of the vehicle being greater than or equal to a threshold soak time, and a time during which the engine is on being greater than a threshold time. In a fourth example of the system, optionally including one or more or each of the first through third examples, indicating the stuck ATWU valve based on the temperature difference between the ECT and the TFT over the duration before the ATWU valve is commanded from the closed position to the open position further comprises: calculating a difference between the ECT and the TFT at a plurality of regular intervals, at each regular interval of the plurality of regular intervals: in response to the difference being less than a threshold temperature difference, updating a cumulative calculated area integral between the ECT and the TFT, and in response to the difference increasing above the threshold temperature difference: dividing the calculated area integral by a time elapsed since the ATWU valve is commanded open to determine an average temperature difference between the ECT and the TFT for a regular interval, in response to the average temperature difference being less than a threshold average temperature difference, not indicating that the ATWU valve is stuck in the closed position, and in response to the average temperature difference not being greater than the threshold average temperature difference, indicating that the ATWU valve is stuck in the closed position. In a fifth example of the system, optionally including one or more or each of the first through fourth examples, indicating that the ATWU valve is stuck in the closed position based on comparing the rate of change of the TFT before and after the ATWU valve is commanded open further comprises: collecting a first minimum number of sample TFT values at regular intervals prior to opening the ATWU valve, performing a first linear regression to calculate a first TFT slope of the first minimum number of sample TFT values, collecting a second minimum number of sample TFT values at regular intervals after opening the ATWU valve, performing a second linear regression to calculate a second TFT slope of the second minimum number of sample TFT values, calculating a difference between the first TFT slope and the second TFT slope, in response to the difference being greater than a threshold difference, not indicating that the ATWU valve is stuck in the closed position, and in response to the difference not being greater than the threshold difference, indicating that the ATWU valve is stuck in the closed position. In a sixth example of the system, optionally including one or more or each of the first through fifth examples, further instructions are stored in the non-transitory memory that when executed, cause the controller to limit an acceleration of the vehicle in response to the stuck ATWU valve being indicated.

The disclosure also provides support for a method for a controller of a vehicle including an active Transmission Warmup (ATWU) valve, the method comprising: based on a calibration parameter being equal to a first value, determining whether the ATWU valve is stuck based on calculating an area integral between a first curve defined by an engine coolant temperature (ECT) and a second curve defined by a transmission fluid temperature (TFT) over a duration before the ATWU valve is commanded open, based on the calibration parameter being equal to a second value, determining whether the ATWU valve is stuck based on calculating a first slope of a first curve defined by TFT measurements taken prior to commanding the ATWU valve open, calculating a second slope of a second curve defined by TFT measurements taken after commanding the ATWU valve open, and comparing the first slope to the second slope, based on the calibration parameter being equal to a third value, determining whether the ATWU valve is stuck based on both calculating the area integral and comparing the first slope to the second slope, in response to at least one of the area integral being less than a first threshold value and a difference between the second slope and the first slope being less than a second threshold value, setting a diagnostic flag, and in response to the diagnostic flag being set, indicating that the ATWU valve is stuck. In a first example of the method, the calibration parameter is equal to the third value, and: in a first condition where the ATWU valve is stuck, the area integral is less than the first threshold value and the difference between the second slope and the first slope is less than the second threshold value, and the diagnostic flag is set, and in a second condition where the ATWU valve is not stuck, the area integral is not less than the first threshold value and the difference between the second slope and the first slope is not less than the second threshold value, and the diagnostic flag is not set. In a second example of the method, optionally including the first example, the calibration parameter is equal to the third value, and: in the first condition where the ATWU valve is stuck, the area integral is less than the first threshold value and the difference between the second slope and the first slope is not less than the second threshold value, and the diagnostic flag is set.