Methods and systems for diagnosing transmission warm-up valve

Systems and methods for diagnosing operation of a transmission warm-up valve are presented. In one example, the transmission warm-up valve is commanded to an open position and an estimated transmission fluid temperature is compared to an actual transmission fluid temperature to determine whether or not the transmission warm-up valve is operating as commanded.

TECHNICAL FIELD

The present description relates to a system and methods for warming an automatic transmission of a vehicle. The methods may be particularly useful for an automatic transmission that is coupled to an engine.

BACKGROUND AND SUMMARY

At lower temperatures, viscosities of fluids in an engine and in a transmission may be greater than when the engine and transmission are warm. The higher viscosities may lead to the engine operating at a higher load and less efficiently. Therefore, it may be desirable to warm engine oil and transmission fluid so that the engine may operate more efficiently as soon as possible after starting. However, if a temperature of transmission fluid does not increase as fast as desired, engine emissions may increase and engine efficiency may be reduced. Therefore, it may be desirable to provide a way of determining whether or not subsystem components related to warming of transmission fluid are operational.

The inventors herein have recognized that it may be desirable to diagnose operation of a device that controls transmission fluid temperature and have developed a method for diagnosing operation of a transmission warm-up valve, comprising: via a controller, estimating a temperature of transmission fluid exiting a heat exchanger; and adjusting operation of a device in response to a difference between the temperature and an actual temperature of transmission fluid exiting the heat exchanger via the controller.

By estimating a temperature of transmission fluid exiting a heat exchanger and adjusting a device in response a difference between the temperature and an actual temperature of transmission fluid exiting the heat exchanger, it may be possible to diagnose operation of an automatic transmission warm-up valve. For example, if the estimated temperature is greater than the actual temperature by more than a predetermined amount, a display may be adjusted to indicate degradation of the automatic transmission warm-up valve. Additionally, operation of an engine and/or transmission may be adjusted in response to indication of automatic transmission warm-up valve degradation.

The present description may provide several advantages. Specifically, the approach may provide an indication of valve degradation that may be indicative of an increase in vehicle emissions. In addition, the approach may provide compensation for engine and/or transmission operation if valve degradation is indicated. Further, the approach may provide an indication of valve operation without having to directly monitor the valve via a dedicated sensor, thereby reducing system financial expense.

The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings. The term “driver” may be referred to throughout this specification and it refers to a human driver or human vehicle operator that is the authorized operator of the vehicle unless otherwise indicated.

DETAILED DESCRIPTION

The present description is related to diagnosing operation of an automatic transmission warm-up valve. The automatic transmission warm-up valve may control warm engine coolant flow into a heat exchanger that may transfer heat from the warm engine coolant to transmission fluid, thereby heating the transmission fluid. The automatic transmission warm-up valve may be opened shortly after a cold engine start to warm transmission fluid. The automatic transmission warm-up valve may be supplied with engine coolant from an engine of the type shown inFIG.1. The engine may be part of a powertrain or driveline as shown inFIG.2. The vehicle may have a heat transfer system as shown inFIG.3. The vehicle and heat transfer system may operate according to the method shown in the block diagrams ofFIGS.4-9. The vehicle may operate according to the method ofFIGS.4-9as shown inFIG.10.

Referring toFIG.1, engine10is an internal combustion engine that comprises a plurality of cylinders, one cylinder33of which is shown inFIG.1. Engine10is controlled by electronic engine controller12. The controller receives signals from the various sensors ofFIG.1and it employs the various actuators ofFIG.1to adjust engine operation based on the received signals and instructions stored in memory of controller12. For example, fuel injection timing, spark timing, and poppet valve operation may be adjusted responsive to engine position as determined from output of an engine position sensor.

Engine10includes combustion chamber30, cylinder33, and cylinder walls32with piston36positioned therein and connected to crankshaft40. Flywheel97and ring gear99are coupled to crankshaft40. Starter96includes pinion shaft98and pinion gear95. Pinion shaft98may selectively advance pinion gear95to engage ring gear99. Starter96may be directly mounted to the front of the engine or the rear of the engine. In some examples, starter96may selectively supply torque to crankshaft40via a chain for example. In one example, starter96is in a base state when not engaged to the engine crankshaft. Combustion chamber30is shown communicating with intake manifold44and exhaust manifold48via respective intake valve52and exhaust valve54. Each intake and exhaust valve may be operated by an intake cam51and an exhaust cam53. The position of intake cam51may be determined by intake cam sensor55. The position of exhaust cam53may be determined by exhaust cam sensor57. Intake cam51and exhaust cam53may be moved relative to crankshaft40.

Fuel injector66is shown positioned to inject fuel directly into cylinder33, which is known to those skilled in the art as direct injection. Alternatively, fuel may be injected to an intake port, which is known to those skilled in the art as port injection. Fuel injector66delivers liquid fuel in proportion to the pulse width of signal from controller12. Fuel is delivered to fuel injector66by a fuel system (not shown) including a fuel tank, fuel pump, and fuel rail (not shown). In addition, intake manifold44is shown communicating with optional electronic throttle62which adjusts a position of throttle plate64to control air flow from air intake42to intake manifold44. In one example, a low pressure direct injection system may be used, where fuel pressure can be raised to approximately 20-30 bar. Alternatively, a high pressure, dual stage, fuel system may be used to generate higher fuel pressures. In some examples, throttle62and throttle plate64may be positioned between intake valve52and intake manifold44such that throttle62is a port throttle.

Controller12is shown inFIG.1as a conventional microcomputer including: microprocessor unit102, input/output ports104, read-exclusive memory106(e.g., non-transitory memory), random access memory108, keep alive memory110, and a conventional data bus. Controller12is shown receiving various signals from sensors coupled to engine10, in addition to those signals previously discussed, including: engine coolant temperature (ECT) from temperature sensor112coupled to cooling sleeve114; a position sensor134coupled to a driver demand pedal130for sensing force applied by human driver132; a measurement of engine manifold absolute pressure (MAP) from pressure sensor122coupled to intake manifold44; an engine position sensor from engine position sensor118sensing crankshaft40position; a measurement of air mass entering the engine from sensor120; pedal position from pedal position sensor154when human driver132applies pedal150to slow the vehicle; and a measurement of throttle position from sensor58. Barometric pressure may also be sensed (sensor not shown) for processing by controller12. In a preferred aspect of the present description, engine position sensor118produces a predetermined number of equally spaced pulses each revolution of the crankshaft from which engine speed (RPM) can be determined.

Controller12may receive input from human/machine interface170. In one example, human/machine interface170may be a touch screen display. In other examples, human/machine interface170may be a key board, pushbutton, or other known interface. Controller12may also display information and data to human/machine interface170.

In some examples, the engine may be coupled to an electric motor/battery system in a hybrid vehicle. Further, in some examples, other engine configurations may be employed, for example a diesel engine.

Referring now toFIG.2, is a block diagram200of a vehicle290including a powertrain or driveline200. The powertrain ofFIG.2includes engine10shown inFIG.1. It may be noted that this example shows a single controller. However, in other examples, the functions and operations performed via controller12may be distributed between a plurality of controllers.

Engine crankshaft40may be coupled to torque converter206, and torque converter206is mechanically coupled to automatic transmission208via transmission input shaft207. Torque converter206may also include a torque converter clutch209. Automatic transmission208includes gear clutches (e.g., gears1-10)210and forward clutch212. Automatic transmission208is a fixed step ratio transmission. The gear clutches210and the forward clutch212may be selectively engaged to change a ratio of an actual total number of turns of input shaft207to an actual total number of turns of wheels218. Gear clutches210may be engaged or disengaged via adjusting fluid supplied to the clutches via shift control solenoid valves (not shown). Torque output from the automatic transmission208may also be relayed to wheels218to propel the vehicle via output shaft215. Specifically, automatic transmission208may transfer an input driving torque at the input shaft207responsive to a vehicle traveling condition before transmitting an output driving torque to the wheels218. Controller12may selectively activate a torque converter clutch209, gear clutches210, and forward clutch212. Controller12may also selectively deactivate or disengages a torque converter clutch209, gear clutches210, and forward clutch212.

In response to a request to increase a speed of vehicle290, controller12may obtain a driver demand torque or power request from a driver demand pedal or other device. Controller12commands engine10to provide the requested torque via one or more torque actuators204. The torque converter clutch209may be locked and gears may be engaged via gear clutches210in response to shift schedules and torque converter clutch lockup schedules that may be based on transmission input shaft torque and vehicle speed.

Engine torque may be controlled by controller12adjusting a combination of spark timing, fuel pulse width, fuel pulse timing, and/or air charge, by controlling throttle opening and/or valve timing, valve lift and boost for turbo- or super-charged engines. In the case of a diesel engine, controller12may control the engine torque output by controlling a combination of fuel pulse width, fuel pulse timing, and air charge. In all cases, engine control may be performed on a cylinder-by-cylinder basis to control the engine torque output.

Controller12may receive transmission input shaft position via a position sensor (not shown) and convert transmission input shaft position into input shaft speed via differentiating a signal from the position sensor. Controller12may receive transmission output shaft torque from a torque sensor (not shown). Controller12may also receive addition transmission information from sensors277, which may include but are not limited to pump output line pressure sensors, transmission hydraulic pressure sensors (e.g., gear clutch fluid pressure sensors), driver present detection switch, driver's door switch, heart beat sensors, and ambient temperature sensors.

In some examples, controller12may communicate with and exchange data with navigation system235(e.g., a second controller). Navigation system235may determine a position and speed of vehicle290via data received from global positioning satellites (not shown). Navigation system235may also receive input via voice commands or via human/machine interface to determine a vehicle destination. Navigation system235may select a travel route based on the vehicle's present position and the vehicle's destination. Navigation system235may determine the travel route based on maps that may be stored within navigation system235. Maps stored in navigation system235may include locations of traffic signs, fueling stations, and other points of interest. In addition, navigation system235may predict when a vehicle speed increase is expected based on the vehicle's present position and mapping data (e.g., road grade, travel route elevation, stored traffic signal or sign locations, etc.). Navigation system235may inform controller12of upcoming or predicted times and/or travel route locations where an increase in vehicle speed is predicted.

Controller12may communicate with satellite275via transceiver220. Alternatively, transceiver220may be a transmitter-receiver. Controller12may receive input (e.g., data including locations and/or times when vehicle speed is predicted to increase and/or decrease) from or broadcast vehicle data to satellite275via transceiver220. Controller12may also communicate with network270(e.g., cellular, vehicle to vehicle, vehicle to infrastructure networks) via transceiver225. Alternatively, transceiver225may be a transmitter-receiver. Controller12may broadcast vehicle data to and receive input from network270via transceiver225. Network270and/or satellite275may communicate with cloud computer289(e.g., a remote server). Cloud computer (e.g., a second controller) may communicate times and/or locations where vehicle speed may be expected to increase or decrease based on the vehicle's present position, road grade, traffic information (e.g., traffic jams, accident locations, etc.), and prior human driver behavior to controller12via satellite275and network270via radio or microwave frequencies288.

Thus, the system ofFIGS.1and2provides for a system for operating a vehicle, comprising: a vehicle including an internal combustion engine and a pedal; and a controller including executable instructions stored in non-transitory memory that cause the controller to inhibit automatic stopping of the internal combustion engine in response to predicted conditions that indicate an operator change of mind during a look ahead window. In a first example, the system further comprises additional instructions to not inhibit automatic stopping of the internal combustion engine in response to the predicted conditions that indicate the operator change of mind during a look ahead window. In a second example that may include the first example, the system includes where the look ahead window is a future time period, and where the look ahead window begins at a present time, or where the look ahead window begins at a time or vehicle location when a driver input to slow the vehicle is applied. In a third example that may include one or more of the first and second examples, the system includes where the look ahead window is a distance in a travel path of the vehicle and further comprises adjusting the distance in response to one or more of a rate of vehicle speed reduction, a location of a traffic sign or signal, or a location of a road profile and/or attribute change. In a fourth example that may include one or more of the first through third examples, the system further comprises additional instructions to predict conditions that indicate the operator change of mind during the look ahead window. In a fifth example that may include one or more of the first through fourth examples, the system includes where the predicted conditions include an increase of vehicle speed. In a sixth example that may include one or more of the first through fifth examples, the system further comprises additional instructions to receive the predicted conditions that indicate the operator change of mind during the look ahead window from a second controller.

Referring now toFIG.3, a heat transfer system300is shown. In this example, heat transfer system300includes an engine coolant loop302and a transmission fluid loop350. The engine coolant loop302includes engine10, radiator320, thermostat322, engine coolant pump315, automatic transmission warm-up valve306, and heat exchanger304. Transmission fluid loop350includes transmission208, transmission fluid pump330, torque converter206, heat exchanger304, and sump332. The direction of flow through engine coolant loop302and transmission fluid loop350is indicated by arrows.

The heat transfer system includes a coolant heat exchanger inlet temperature sensor310, a coolant heat exchanger outlet sensor308, a transmission fluid heat exchanger inlet temperature sensor314, and a transmission fluid heat exchanger outlet temperature sensor312for sensing coolant and transmission fluid temperatures at heat exchanger304. Coolant heat exchanger inlet temperature sensor310senses a temperature of coolant entering heat exchanger304. Coolant heat exchanger outlet temperature sensor308senses a temperature of coolant exiting heat exchanger304. Transmission fluid heat exchanger inlet temperature sensor314senses a temperature of transmission fluid entering heat exchanger304. Transmission fluid heat exchanger outlet temperature sensor312senses a temperature of transmission fluid exiting heat exchanger304.

The heat transfer system300may supply warm engine coolant to heat exchanger304via opening automatic transmission warm-up valve306. The warm coolant may transfer thermal energy to transmission fluid that is circulated through heat exchanger304. Controller12may open and close automatic transmission warm-up valve306in response to temperatures sensed via temperature sensors308-314and other vehicle operating conditions.

The system ofFIGS.1-3provides for a transmission warming system, comprising: an internal combustion engine; an automatic transmission; a heat exchanger; an automatic transmission warm-up valve; and a controller including executable instructions stored in non-transitory memory that cause the controller to generate a comparison of an estimate of a temperature of transmission fluid exiting the heat exchanger to an actual temperature of transmission fluid exiting the heat exchanger, and adjust operation of the automatic transmission or the internal combustion engine in response to the comparison. In a first example, the system includes where the estimate of the temperature of the transmission fluid is based on a commanded state of the automatic transmission warm-up valve. In a second example that may include the first example, the system includes where the estimate of the temperature of the transmission fluid is also based on a specific heat acceptance value of the heat exchanger. In a third example that may include one or both of the first and second examples, the system includes where the estimate of the temperature of the transmission fluid is further based on engine coolant temperature. In a fourth example that may include one or more of the first through third examples, the system includes where the estimate of the temperature of the transmission fluid is further based on engine speed. In a fifth example that may include one or more of the first through fourth examples, the system includes where adjusting operating of the transmission includes modifying a transmission shift schedule. In a sixth example that may include one or more of the first through fifth examples, the system includes where adjusting operation of the engine includes adjusting engine valve timing.

Referring now toFIGS.4-9, block diagrams for estimating a transmission fluid temperature and diagnosing operation of the automatic transmission warm-up valve are shown. The method described by the block diagrams ofFIGS.4-9may be incorporated into one or more controllers (e.g.,12ofFIG.1) as executable instructions stored in non-transitory memory (e.g., read-exclusive memory). The executable instructions may cooperate with the system ofFIGS.1-3to retrieve information or data from sensors and adjust positions of actuators in the real-world. The arrows inFIGS.4-9represent the direction of data flow in the block diagrams.

Block diagram400shows signals and blocks that operate to provide an indication or absence of automatic transmission warm-up (ATWU) valve degradation according to an estimated transmission fluid temperature and an actual valve of the transmission fluid temperature.

At block402, engine speed (RPM) and transmission fluid flow rate are received as inputs to block402. The inputs are applied to reference tables or functions as shown inFIG.5. Block402outputs a transmission fluid specific heat acceptance value for heat exchanger304ofFIG.3that is input to block404.

At block404, engine coolant temperature, transmission output temperature (e.g., transmission fluid temperature at temperature sensor314ofFIG.3), and the transmission fluid specific heat acceptance value for heat exchanger304are received as inputs to block404. The inputs are applied to reference tables or functions as shown inFIG.6. Block404outputs a heat exchanger heat increase value for the transmission fluid that exits the heat exchanger. The heat exchanger heat increase value is input to block406.

At block406, a heat exchanger heat increase value for the transmission fluid that exits the heat exchanger, transmission output temperature, and the commanded automatic transmission warm-up (ATWU) valve operating state are received as inputs to block406. The inputs are applied to reference tables or functions as shown inFIG.7. Block406outputs a modeled or estimated transmission fluid temperature at the outlet of the heat exchanger (e.g., an estimate of the temperature that is sensed via temperature sensor312) that includes compensation for the commanded ATWU state. The modeled or estimated transmission fluid temperature at the outlet of the heat exchanger is input to block408.

At block408, modeled or estimated transmission fluid at the outlet of the heat exchanger and actual transmission fluid temperature at the outlet of the heat exchanger are received as inputs to block408. The inputs are applied to reference tables or functions as shown inFIG.8. Block408outputs a modeled or estimated transmission fluid temperature that is output from the heat exchanger (e.g., an estimate of the temperature that is sensed via temperature sensor312). The modeled or estimated transmission fluid temperature is input to block410.

At block410, modeled or estimated transmission fluid at the outlet of the heat exchanger is compared to the actual transmission fluid temperature at the outlet of the heat exchanger. If the modeled or estimated transmission fluid temperature is greater than the actual transmission fluid temperature by more than a predetermined amount, block410indicated automatic transmission warm-up valve degradation. Otherwise, block410indicates that the automatic transmission warm-up valve is not degraded. Block410outputs an indication as to whether or not the automatic transmission warm-up valve is degraded to block412.

At block412, method400performs actions to mitigate degradation of the automatic transmission warm-up valve. In particular, method400may adjust a human/machine interface to indicate automatic transmission warm-up valve degradation. In addition, method400may adjust engine operation in response to automatic transmission warm-up valve degradation. Adjusting engine operation may include adjusting engine spark timing and adjusting engine poppet valve timing so that less engine heat may be rejected to engine coolant during engine cold starting, thereby increasing system efficiency when less engine heat may be transferred to the transmission. For example, spark may be advanced sooner after a cold start if automatic transmission warm-up valve degradation is present. Further, exhaust valve timing may be advanced sooner after a cold engine start if automatic transmission warm-up valve degradation is present.

Method400may also adjust transmission operation if automatic transmission warm-up valve degradation is indicated. For example, method400may adjust a transmission shift schedule so that transmission clutches may take longer to close. Additionally, adjustments to the torque converter clutch lock-up schedule may be performed when automatic transmission warm-up valve degradation is indicated.

Thus, the method ofFIG.4estimates a transmission fluid temperature and compares the estimated transmission fluid temperature to an actual transmission fluid temperature that is determined via a temperature sensor. If the estimated transmission fluid temperature is greater than the actual transmission fluid temperature when the automatic transmission warm-up valve is commanded open, then automatic transmission warm-up valve degradation may be indicated.

Turning now toFIG.5, a detailed view of the contents of block402ofFIG.4is shown. In particular, engine speed (revolutions/min (RPM)) is input to block502. Block502represents a one dimensional table that outputs an engine coolant flow rate through the heat exchanger when the automatic transmission warm-up valve is fully open according to the engine speed input. The engine coolant flow rate is input into block503.

Block503represents a two dimensional table that outputs a transmission fluid specific heat acceptance value for the heat exchanger. The values in the table are referenced by the engine coolant flow rate and the transmission fluid flow rate through the heat exchanger. The transmission fluid specific heat acceptance value is output from block402and it has units of kiloWatts/engine coolant inlet temperature difference with respect to the engine coolant output temperature.

In this way, the operational characteristics of the heat exchanger are used to estimate the transmission fluid temperature. By applying the operational characteristics of the heat exchanger to estimate transmission fluid temperature, accuracy of the estimated transmission fluid temperature may be increased.

Referring now toFIG.6, a detailed view of the contents of block404ofFIG.4is shown. Specifically, engine coolant temperature, transmission output temperature (e.g., temperature of transmission fluid at the location of temperature sensor314ofFIG.4), and transmission fluid specific heat acceptance values for the heat exchanger are received to block404. The engine coolant temperature and the transmission output temperature are input to block602. Block602represents an arithmetic block where engine coolant temperature is subtracted from the transmission output temperature. The result from block602is input to block603along with the transmission fluid specific heat acceptance values for the heat exchanger. Block603is a multiplication block that multiplies the result output from block602by the transmission fluid specific heat acceptance values for the heat exchanger. Block603outputs the result of a heat exchanger heat or temperature increase.

Moving on toFIG.7, a detailed view of the contents of block406ofFIG.4is shown. Block406receives a constant (0), an operating state (e.g., open/closed) for the automatic transmission warm-up (ATWU) valve, and the heat exchanger heat or temperature increase. In this example, block702is a switching block that outputs the value of one input (0) or the value of a second input (heat exchanger heat increase) to block703depending on the operating state of the automatic transmission warm-up valve. If the automatic transmission warm-up valve is closed, block702outputs a value of zero. If the automatic transmission warm-up valve is open, block702outputs the heat exchanger heat increase value. Block703applies a first order low pass filter to values that are input to block703and block703outputs a filtered value to block704. Block704multiplies the output of block703by a scalar value and outputs the result to block706. At block706, the transmission output temperature is added to the output of block704to generate a modeled transmission output fluid temperature.

Referring now toFIG.8, a detailed view of the contents of block408ofFIG.4is shown. Block408receives modeled heat exchanger output transmission fluid temperature and actual transmission fluid temperature as inputs to block802. Block802is an arithmetic block that subtracts actual transmission fluid temperature from modeled heat exchanger output transmission fluid temperature and it outputs the result to block804. Block804applies a first order low pass filter to the output of block802and the result is delivered to block806where it is multiplied by a scalar value and the result is supplied to block808. Block808is another arithmetic block and it adds the output of block816to the output of block806and the result is an estimated transmission fluid temperature output from the heat exchanger (e.g.,304ofFIG.3).

A system clock810and a constant are input to block814. Block812represents the scalar constant value and block814represents a greater than block that compares the output of the system clock810to the scalar value that is output from block812. If the output of system clock801is greater than the output of block812, block814outputs a value of logical one. Otherwise, block814outputs a value of logical zero. Block816is a switching block that outputs the value corresponding to the output of block820or the value of a second input (transmission fluid temperature) to block808depending on the output of block814. If the output of block814is a logical zero, block816outputs the output of block820. If the output of block814is a logical one, block816outputs the transmission fluid temperature value. Block820is a time delay block with an output that is delayed by one time step and the output of block808is supplied to the input of block820.

Turning now toFIG.9, a detailed view of the contents of block410ofFIG.4are shown. Block410receives an estimated transmission fluid temperature at the output of the heat exchanger, commanded automatic transmission warm-up valve state, and actual transmission fluid temperature at the output of the heat exchanger. If the estimated transmission fluid temperature at the output of the heat exchanger is greater than the actual transmission fluid temperature at the output of the heat exchanger by more than a predetermined temperature amount and the automatic transmission warm-up valve is commanded open, block902outputs a logical one to indicate automatic transmission warm-up valve degradation. If the estimated transmission fluid temperature at the output of the heat exchanger is not greater than the actual transmission fluid temperature at the output of the heat exchanger by more than a predetermined temperature amount and the automatic transmission warm-up valve is commanded open, block902outputs a logical zero to indicate no automatic transmission warm-up valve degradation. If the estimated transmission fluid temperature at the output of the heat exchanger is greater than the actual transmission fluid temperature at the output of the heat exchanger by more than a predetermined temperature amount and the automatic transmission warm-up valve is not commanded open, block902outputs a logical zero to indicate no automatic transmission warm-up valve degradation. If the estimated transmission fluid temperature at the output of the heat exchanger is not greater than the actual transmission fluid temperature at the output of the heat exchanger by more than a predetermined temperature amount and the automatic transmission warm-up valve is commanded open, block902outputs a logical zero to indicate no automatic transmission warm-up valve degradation.

In this way, the method of block diagrams4-9may determine whether or not an automatic transmission warm-up valve is degraded or not degraded. The determination of degraded or not degraded may be based on a commanded position of the automatic transmission warm-up valve and an estimated transmission fluid temperature.

The method ofFIGS.4-9provides for a method for diagnosing operation of a transmission warm-up valve, comprising: via a controller, estimating a temperature of transmission fluid exiting a heat exchanger; and adjusting operation of a device in response to a difference between the temperature and an actual temperature of transmission fluid exiting the heat exchanger via the controller. In a first example, the method includes where estimating the temperature of transmission fluid includes adjusting the temperature in response to a specific heat acceptance value of the heat exchanger. In a second example that may include the first example, the method includes where the specific heat acceptance value is a function of a flow rate of engine coolant through the heat exchanger. In a third example that may include one or both of the first and second examples, the method includes where the specific heat acceptance value is also based on a flow rate of transmission fluid through the heat exchanger. In a fourth example that may include one or more of the first through third examples, the method includes where the device is a transmission. In a fifth example that may include one or more of the first through fourth examples, the method includes where the device is an engine. In a sixth example that may include one or more of the first through fifth examples, the method includes where the device is a human/machine interface. In a seventh example that may include one or more of the first through sixth examples, the method includes where the temperature is estimated based on a commanded position of the transmission warm-up valve.

The method ofFIGS.4-9also provides for a method for diagnosing operation of a transmission warm-up valve, comprising: via a controller, commanding the transmission warm-up valve to a predetermined state; and judging whether or not the transmission warm-up valve is in the predetermined state in response to an estimated temperature of transmission fluid exiting a heat exchanger. In a first example, the method includes where the estimated temperature of the transmission fluid is compared to an actual temperature of the transmission fluid. In a second example that may include the first example, the method includes where the transmission warm-up valve is determined to be degraded when the estimated temperature of the transmission fluid exceeds the actual temperature of the transmission fluid by a predetermined temperature. In a third example that may include one or both of the first and second examples, the method further comprises adjusting operation of a transmission or an engine in response to whether or not the transmission warm-up is judged to be in the predetermined state. In a fourth example that may include one or more of the first through third examples, the method includes where the predetermined state is an open state.

Referring now toFIG.10, an example vehicle operating sequence according to the method ofFIGS.4-9is shown. The operating sequence ofFIG.10may be generated via the system ofFIGS.1-3in cooperation with the method ofFIGS.4-9. The plots ofFIG.10are time aligned and the vertical lines indicate times of interest in the sequence.

The first plot from the top ofFIG.10is a plot of engine coolant temperature versus time. The vertical axis represents the engine coolant temperature and the engine coolant temperature increases in the direction of the vertical axis arrow. The horizontal axis represents time and the amount of time increases from the left side of the plot to the right side of the plot. Trace1002represents the engine coolant temperature.

The second plot from the top ofFIG.10is a plot of engine coolant temperature versus time. The vertical axis represents the engine coolant temperature and the engine coolant temperature increases in the direction of the vertical axis arrow. The horizontal axis represents time and the amount of time increases from the left side of the plot to the right side of the plot. Trace1004represents the engine coolant temperature.

The third plot from the top ofFIG.10is a plot of estimated or modeled transmission fluid temperature at an outlet of an engine coolant to transmission fluid heat exchanger. The vertical axis represents estimated or modeled transmission fluid temperature at the outlet of the engine coolant to transmission fluid heat exchanger and the estimated or modeled transmission fluid temperature increases in the direction of the vertical axis arrow. The horizontal axis represents time and the amount of time increases from the left side of the plot to the right side of the plot. Trace1006represents the estimated or modeled transmission fluid temperature at the outlet of the engine coolant to transmission fluid heat exchanger.

The fourth plot from the top ofFIG.10is a plot of commanded automatic transmission warm-up valve operating state versus time. The vertical axis represents commanded automatic transmission warm-up valve operating state and the automatic transmission warm-up valve is commanded open when trace1008is near the vertical axis arrow. The automatic transmission warm-up valve is commanded closed when trace1008is near the horizontal axis. The horizontal axis represents time and the amount of time increases from the left side of the plot to the right side of the plot. Trace1008represents the commanded automatic transmission warm-up valve state.

The fifth plot from the top ofFIG.10is a plot of automatic transmission warm-up valve degradation state versus time. The vertical axis represents automatic transmission warm-up valve degradation state and the automatic warm-up valve is determined to be degraded when trace1010is near the vertical axis arrow. The automatic transmission warm-up valve is determined not degraded when trace1010is near the horizontal axis. The horizontal axis represents time and the amount of time increases from the left side of the plot to the right side of the plot. Trace1010represents the automatic transmission warm-up valve degradation state.

At time t0, the engine is cold started and engine coolant temperature begins to rise. The automatic transmission warm-up valve is fully closed to allow the engine to heat faster than if the automatic transmission warm-up valve were open so that engine emissions may be reduced. The modeled transmission fluid temperature and the actual transmission fluid temperatures begin to gradually increase since the engine is rotating the torque converter, which begins to heat the transmission fluid. The automatic transmission warm-up valve is not indicated as being degraded.

At time t1, the engine coolant temperature reaches a threshold temperature, thereby causing the controller to command the automatic transmission warm-up valve fully open. The modeled or estimated transmission fluid temperature at the outlet of the engine coolant to transmission fluid heat exchanger begins to increase at a faster rate. The automatic transmission warm-up valve remains commanded fully open and it is not indicated as being degraded.

At time t2, the engine coolant temperature has leveled off and the modeled transmission fluid temperature at the outlet of the engine coolant to transmission fluid heat exchanger has increased much faster than the actual transmission fluid temperature, which causes the automatic transmission warm-up valve to be determined to be degraded. The automatic transmission warm-up valve remains commanded fully open, but the automatic transmission warm-up valve is indicated as being degraded because the actual temperature of transmission fluid is significantly less than the estimated or modeled automatic transmission fluid temperature, which may indicate that the valve has not opened.

In this way, an automatic transmission warm-up valve may be diagnosed as not being degraded or being degraded. The determination may be based on commanded valve state and temperature of transmission fluid exiting an engine coolant to transmission fluid heat exchanger.

As will be appreciated by one of ordinary skill in the art, methods described herein may represent one or more of any number of processing strategies such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. As such, various steps or functions illustrated may be performed in the sequence illustrated, in parallel, or in some cases omitted. Likewise, the order of processing is not necessarily required to achieve the objects, features, and advantages described herein, but is provided for ease of illustration and description. Although not explicitly illustrated, one of ordinary skill in the art will recognize that one or more of the illustrated steps or functions may be repeatedly performed depending on the particular strategy being used. Further, the described actions, operations, methods, and/or functions may graphically represent code to be programmed into non-transitory memory of the computer readable storage medium in the engine control system.