Patent Publication Number: US-2023147854-A1

Title: Methods and system for de-icing a valve of an exhaust system

Description:
FIELD 
     The present description relates to methods and a system for de-icing a valve in an exhaust system of an internal combustion engine. 
     BACKGROUND AND SUMMARY 
     An engine may be equipped with an exhaust system that includes an exhaust tuning valve. The exhaust tuning valve may change an exhaust note or the sound of exhaust passing through the vehicle&#39;s exhaust system. The exhaust tuning valve may open to direct exhaust gases through a lower resistance passage, thereby increasing exhaust noise. On the other hand, the exhaust tuning valve may be closed to route exhaust gas through sound deadening chambers that tend to reduce exhaust noise. However, when ambient temperatures are near or less than a temperature at which water freezes, the exhaust tuning valve may stick in a fully closed position. If the exhaust tuning valve does not operate as expected due to freezing, the vehicle&#39;s operator may become concerned that the vehicle is operating improperly. In addition, diagnostic trouble codes may be set within a vehicle controller, which may cause additional concern for the vehicle&#39;s operator. 
     The inventor herein has recognized the above-mentioned issues and has developed a method for operating an engine, comprising: adjusting a position of a valve in an exhaust system of the engine via a controller in response to ambient temperature being within a threshold temperature of a temperature at which water freezes and ambient relative humidity being greater than a threshold relative humidity. 
     By adjusting a position of a valve in an exhaust system of an engine before ambient temperature reaches a temperature at which water freezes when ambient humidity is greater than a threshold, it may be possible to clear water from an area where the valve seats to the exhaust system so that a possibility of a stuck valve in the exhaust system may be avoided. In addition, a minimum opening amount of the valve in the exhaust system may be increased so that if there is water in the exhaust system, less surface area may be provided for the water to freeze and couple the valve to the exhaust system. 
     The present description may provide several advantages. In particular, the approach may prevent transient diagnostic codes from being displayed. Further, the approach may improve customer satisfaction. In addition, the approach may reduce vehicle warranty costs. 
     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. 
     It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The advantages described herein will be more fully understood by reading an example of an embodiment, referred to herein as the Detailed Description, when taken alone or with reference to the drawings, where: 
         FIG.  1    is a schematic diagram of an engine; 
         FIG.  2    is a schematic diagram of a hybrid vehicle driveline; 
         FIG.  3    is a plot of an example vehicle operating sequence according to the method of  FIG.  4   ; 
         FIG.  4    shows a flowchart of a method for operating a vehicle; and 
         FIG.  5    shows a schematic of an example circuit for waking-up a controller to adjust a position of a valve in an exhaust system of a vehicle. 
     
    
    
     DETAILED DESCRIPTION 
     The present description is related to operating a vehicle that includes a valve in an exhaust system of an internal combustion engine. A position of the valve may be adjusted to provide a varying exhaust note. The valve may be subject to operating conditions that may cause the valve to freeze in an open or closed position. The valve may be included in an exhaust system of an engine of the type shown in  FIG.  1   . The engine may be included in a hybrid vehicle of the type shown in  FIG.  2    or another known type of hybrid vehicle. The valve and engine may be operated as shown in the sequence of  FIG.  3    according to the method of  FIG.  4   . A controller may wake and operate the valve according to input from an electrical circuit as shown in  FIG.  5    or via an alternative circuit. 
     Referring to  FIG.  1   , internal combustion engine  10 , comprising a plurality of cylinders, one cylinder of which is shown in  FIG.  1   , is controlled by electronic engine controller  12 . The controller  12  receives signals from the various sensors shown in  FIGS.  1  and  2   . The controller  12  employs the actuators shown in  FIGS.  1  and  2    to adjust engine and driveline operation based on the received signals and instructions stored in memory of controller  12 . 
     Engine  10  is comprised of cylinder head  35  and block  33 , which include combustion chamber  30  and cylinder walls  32 . Piston  36  is positioned therein and reciprocates via a connection to crankshaft  40 . Flywheel  97  and ring gear  99  are coupled to crankshaft  40 . Optional starter  96  (e.g., low voltage (operated with less than 30 volts) electric machine) includes pinion shaft  98  and pinion gear  95 . Pinion shaft  98  may selectively advance pinion gear  95  to engage ring gear  99 . Starter  96  may be directly mounted to the front of the engine or the rear of the engine. In some examples, starter  96  may selectively supply power to crankshaft  40  via a belt or chain. In one example, starter  96  is in a base state when not engaged to the engine crankshaft. Combustion chamber  30  is shown communicating with intake manifold  44  and exhaust manifold  48  via respective intake valve  52  and exhaust valve  54 . Each intake and exhaust valve may be operated by an intake cam  51  and an exhaust cam  53 . The position of intake cam  51  may be determined by intake cam sensor  55 . The position of exhaust cam  53  may be determined by exhaust cam sensor  57 . Intake valve  52  may be selectively activated and deactivated by valve activation device  59 . Exhaust valve  54  may be selectively activated and deactivated by valve activation device  58 . Valve activation devices  58  and  59  may be electro-mechanical devices. 
     Direct fuel injector  66  is shown positioned to inject fuel directly into cylinder  30 , which is known to those skilled in the art as direct injection. Port fuel injector  67  is shown positioned to inject fuel into the intake port of cylinder  30 , which is known to those skilled in the art as port injection. Fuel injectors  66  and  67  deliver liquid fuel in proportion to pulse widths provided by controller  12 . Fuel is delivered to fuel injectors  66  and  67  by a fuel system (not shown) including a fuel tank, fuel pump, and fuel rail (not shown). 
     In addition, intake manifold  44  is shown communicating with turbocharger compressor  162  and engine air intake  42 . In other examples, compressor  162  may be a supercharger compressor. Shaft  161  mechanically couples turbocharger turbine  164  to turbocharger compressor  162 . Optional electronic throttle  62  adjusts a position of throttle plate  64  to control air flow from compressor  162  to intake manifold  44 . Pressure in boost chamber  45  may be referred to a throttle inlet pressure since the inlet of throttle  62  is within boost chamber  45 . The throttle outlet is in intake manifold  44 . In some examples, throttle  62  and throttle plate  64  may be positioned between intake valve  52  and intake manifold  44  such that throttle  62  is a port throttle. Compressor recirculation valve  47  may be selectively adjusted to a plurality of positions between fully open and fully closed. Waste gate  163  may be adjusted via controller  12  to allow exhaust gases to selectively bypass turbine  164  to control the speed of compressor  162 . Air filter  43  cleans air entering engine air intake  42 . 
     Distributorless ignition system  88  provides an ignition spark to combustion chamber  30  via spark plug  92  in response to controller  12 . Combustion gases may exit engine  10  and enter exhaust system  127 . Exhaust system  127  includes an exhaust manifold, a universal exhaust gas oxygen (UEGO) sensor  126 , and a three-way catalyst  70 . The exhaust sensor  126  is located upstream of three-way catalyst  70  according to a direction of exhaust gas flow. In some examples, a two-state exhaust gas oxygen sensor may be substituted for UEGO sensor  126 . 
     Three-way catalyst  70  may include multiple bricks. An exhaust tuning valve  175  is positioned downstream of three-way catalyst  70 . The exhaust tuning valve  175  may include a butterfly valve  164  in a first passage  166  and baffling  176  in a second passage  165 . Substantially all engine exhaust may flow through second passage  165  when butterfly valve  164  is in a closed position. Substantially all engine exhaust may flow through first passage  166  when butterfly valve  164  is fully open. A sound level of exhaust flowing through second passage  165  may be muffled or reduced. A sound level of exhaust flowing through first passage  166  may be less muffled or reduced as compared to if the exhaust flowed through the second passage  165 . 
     Controller  12  is shown in  FIG.  1    as a conventional microcomputer including: microprocessor unit  102 , input/output ports  104 , read-only memory  106  (e.g., non-transitory memory), random access memory  108 , keep alive memory  110 , and a conventional data bus. Controller  12  is shown receiving various signals from sensors coupled to engine  10 , in addition to those signals previously discussed, including: engine coolant temperature (ECT) from temperature sensor  112  coupled to cooling sleeve  114 ; a position sensor  134  coupled to an accelerator pedal  130  (e.g., a human/machine interface) for sensing force applied by human driver  132 ; a position sensor  154  coupled to brake pedal  150  (e.g., a human/machine interface) for sensing force applied by human driver  132 , a measurement of engine manifold pressure (MAP) from pressure sensor  122  coupled to intake manifold  44 ; an engine position sensor from a Hall effect sensor  118  sensing crankshaft  40  position; a measurement of air mass entering the engine from sensor  120 ; a measurement of ambient temperature via temperature sensor  170 ; a measurement of ambient humidity (e.g., relative humidity) from humidity sensor  171 ; and a measurement of throttle position from sensor  68 . Barometric pressure may also be sensed (sensor not shown) for processing by controller  12 . In a preferred aspect of the present description, engine position sensor  118  produces a predetermined number of equally spaced pulses every revolution of the crankshaft from which engine speed (RPM) can be determined. 
     Controller  12  may also receive input from human/machine interface  11 . A request to start the engine or vehicle may be generated via a human and input to the human/machine interface  11 . The human/machine interface  11  may be a touch screen display, pushbutton, key switch or other known device. 
     During operation, each cylinder within engine  10  typically undergoes a four stroke cycle: the cycle includes the intake stroke, compression stroke, expansion stroke, and exhaust stroke. During the intake stroke, generally, the exhaust valve  54  closes and intake valve  52  opens. Air is introduced into combustion chamber  30  via intake manifold  44 , and piston  36  moves to the bottom of the cylinder so as to increase the volume within combustion chamber  30 . The position at which piston  36  is near the bottom of the cylinder and at the end of its stroke (e.g. when combustion chamber  30  is at its largest volume) is typically referred to by those of skill in the art as bottom dead center (BDC). 
     During the compression stroke, intake valve  52  and exhaust valve  54  are closed. Piston  36  moves toward the cylinder head so as to compress the air within combustion chamber  30 . The point at which piston  36  is at the end of its stroke and closest to the cylinder head (e.g. when combustion chamber  30  is at its smallest volume) is typically referred to by those of skill in the art as top dead center (TDC). In a process hereinafter referred to as injection, fuel is introduced into the combustion chamber. In a process hereinafter referred to as ignition, the injected fuel is ignited by known ignition means such as spark plug  92 , resulting in combustion. 
     During the expansion stroke, the expanding gases push piston  36  back to BDC. Crankshaft  40  converts piston movement into a rotational power of the rotary shaft. Finally, during the exhaust stroke, the exhaust valve  54  opens to release the combusted air-fuel mixture to exhaust manifold  48  and the piston returns to TDC. Note that the above is shown merely as an example, and that intake and exhaust valve opening and/or closing timings may vary, such as to provide positive or negative valve overlap, late intake valve closing, or various other examples. 
       FIG.  2    is a block diagram of a vehicle  225  including a powertrain or driveline  200 . The powertrain of  FIG.  2    includes engine  10  shown in  FIG.  1   . Powertrain  200  is shown including vehicle system controller  255 , engine controller  12 , electric machine controller  252 , transmission controller  254 , energy storage device controller  253 , and brake controller  250 . The controllers may communicate over controller area network (CAN)  299 . Each of the controllers may provide information to other controllers such as power output limits (e.g., power output of the device or component being controlled not to be exceeded), power input limits (e.g., power input of the device or component being controlled not to be exceeded), power output of the device being controlled, sensor and actuator data, diagnostic information (e.g., information regarding a degraded transmission, information regarding a degraded engine, information regarding a degraded electric machine, information regarding degraded brakes). Further, the vehicle system controller  255  may provide commands to engine controller  12 , electric machine controller  252 , transmission controller  254 , and brake controller  250  to achieve driver input requests and other requests that are based on vehicle operating conditions. 
     For example, in response to a driver releasing an accelerator pedal and vehicle speed, vehicle system controller  255  may request a desired wheel power or a wheel power level to provide a desired rate of vehicle deceleration. The requested desired wheel power may be provided by vehicle system controller  255  requesting a first braking power from electric machine controller  252  and a second braking power from engine controller  12 , the first and second powers providing a desired driveline braking power at vehicle wheels  216 . Vehicle system controller  255  may also request a friction braking power via brake controller  250 . The braking powers may be referred to as negative powers since they slow driveline and wheel rotation. Positive power may maintain or accelerate driveline and wheel rotation. 
     In other examples, the partitioning of controlling powertrain devices may be partitioned differently than is shown in  FIG.  2   . For example, a single controller may take the place of vehicle system controller  255 , engine controller  12 , electric machine controller  252 , transmission controller  254 , and brake controller  250 . Alternatively, the vehicle system controller  255  and the engine controller  12  may be a single unit while the electric machine controller  252 , the transmission controller  254 , and the brake controller  250  are standalone controllers. 
     In this example, powertrain  200  may be powered by engine  10  and electric machine  240 . In other examples, engine  10  may be omitted. Engine  10  may be started with an engine starting system shown in  FIG.  1   , via BISG  219 , or via driveline integrated starter/generator (ISG)  240  also known as an integrated starter/generator. A speed of BISG  219  may be determined via optional BISG speed sensor  203 . Driveline ISG  240  (e.g., high voltage (operated with greater than 30 volts) electrical machine) may also be referred to as an electric machine, motor, and/or generator. Further, power of engine  10  may be adjusted via power actuator  204 , such as a fuel injector, throttle, etc. 
     BISG  219  is mechanically coupled to engine  10  via belt  231 . BISG may be coupled to crankshaft  40  or a camshaft (e.g.,  51  or  53  of  FIG.  1   ). BISG may operate as a motor when supplied with electrical power via electric energy storage device  275  or low voltage battery  280 . BISG may operate as a generator supplying electrical power to electric energy storage device  275  or low voltage battery  280 . Bi-directional DC/DC converter  281  may transfer electrical energy from a high voltage buss  274  to a low voltage buss  273  or vice-versa. Low voltage battery  280  is electrically coupled to low voltage buss  273 . Electric energy storage device  275  is electrically coupled to high voltage buss  274 . Low voltage battery  280  selectively supplies electrical energy to starter motor  96 . 
     An engine output power may be transmitted to an input or first side of powertrain disconnect clutch  235  through dual mass flywheel  215 . Disconnect clutch  236  may be electrically or hydraulically actuated. The downstream or second side  234  of disconnect clutch  236  is shown mechanically coupled to ISG input shaft  237 . 
     Disconnect clutch  236  may be fully closed when engine  10  is supplying power to vehicle wheels  216 . Disconnect clutch  236  may be fully open when engine  10  is stopped (e.g., not combusting fuel) or when engine  10  is supplying power to BISG  219  and BISG  219  is generating electrical charge to charge electric energy storage device  275  or supplying electrical charge to ISG  240 . 
     ISG  240  may be operated to provide power to powertrain  200  or to convert powertrain power into electrical energy to be stored in electric energy storage device  275  in a regeneration mode. In addition, ISG  240  may rotate engine  10  from a position where the engine has stopped rotating to start or motor the engine. ISG  240  is in electrical communication with energy storage device  275 . ISG  240  has a higher output power capacity than starter  96  shown in  FIG.  1    or BISG  219 . Further, ISG  240  directly drives powertrain  200  or is directly driven by powertrain  200 . There are no belts, gears, or chains to couple ISG  240  to powertrain  200 . Rather, ISG  240  rotates at the same rate as powertrain  200 . Electrical energy storage device  275  (e.g., high voltage battery or power source) may be a battery, capacitor, or inductor. The downstream side of ISG  240  is mechanically coupled to the impeller  285  of torque converter  206  via shaft  241 . The upstream side of the ISG  240  is mechanically coupled to the disconnect clutch  236 . ISG  240  may provide a positive power or a negative power to powertrain  200  via operating as a motor or generator as instructed by electric machine controller  252 . 
     Torque converter  206  includes a turbine  286  to output power to input shaft  270 . Input shaft  270  mechanically couples torque converter  206  to automatic transmission  208 . Torque converter  206  also includes a torque converter bypass lock-up clutch  212  (TCC). Power is directly transferred from impeller  285  to turbine  286  when TCC is locked. TCC is electrically operated by controller  12 . Alternatively, TCC may be hydraulically locked. In one example, the torque converter may be referred to as a component of the transmission. 
     When torque converter lock-up clutch  212  is fully disengaged, torque converter  206  transmits engine power to automatic transmission  208  via fluid transfer between the torque converter turbine  286  and torque converter impeller  285 , thereby enabling power multiplication. In contrast, when torque converter lock-up clutch  212  is fully engaged, the engine output power is directly transferred via the torque converter clutch to an input shaft  270  of transmission  208 . Alternatively, the torque converter lock-up clutch  212  may be partially engaged, thereby enabling the amount of power directly relayed to the transmission to be adjusted. The transmission controller  254  may be configured to adjust the amount of power transmitted by torque converter  212  by adjusting the torque converter lock-up clutch in response to various engine operating conditions, or based on a driver-based engine operation request. 
     Torque converter  206  also includes pump  283  that pressurizes fluid to operate disconnect clutch  236 , forward clutch  210 , and gear clutches  211 . Pump  283  is driven via impeller  285 , which rotates at a same speed as ISG  240 . 
     Automatic transmission  208  includes gear clutches (e.g., gears  1 - 10 )  211  and forward clutch  210 . Automatic transmission  208  is a fixed ratio transmission. Alternatively, transmission  208  may be a continuously variable transmission that has a capability of simulating a fixed gear ratio transmission and fixed gear ratios. The gear clutches  211  and the forward clutch  210  may be selectively engaged to change a ratio of an actual total number of turns of input shaft  270  to an actual total number of turns of wheels  216 . Gear clutches  211  may be engaged or disengaged via adjusting fluid supplied to the clutches via shift control solenoid valves  209 . Power output from the automatic transmission  208  may also be relayed to wheels  216  to propel the vehicle via output shaft  260 . Specifically, automatic transmission  208  may transfer an input driving power at the input shaft  270  responsive to a vehicle traveling condition before transmitting an output driving power to the wheels  216 . Transmission controller  254  selectively activates or engages TCC  212 , gear clutches  211 , and forward clutch  210 . Transmission controller also selectively deactivates or disengages TCC  212 , gear clutches  211 , and forward clutch  210 . 
     Further, a frictional force may be applied to wheels  216  by engaging friction wheel brakes  218 . In one example, friction wheel brakes  218  may be engaged in response to a human driver pressing their foot on a brake pedal (not shown) and/or in response to instructions within brake controller  250 . Further, brake controller  250  may apply brakes  218  in response to information and/or requests made by vehicle system controller  255 . In the same way, a frictional force may be reduced to wheels  216  by disengaging wheel brakes  218  in response to the human driver releasing their foot from a brake pedal, brake controller instructions, and/or vehicle system controller instructions and/or information. For example, vehicle brakes may apply a frictional force to wheels  216  via controller  250  as part of an automated engine stopping procedure. 
     In response to a request to accelerate vehicle  225 , vehicle system controller may obtain a driver demand power or power request from an accelerator pedal or other device. Vehicle system controller  255  then allocates a fraction of the requested driver demand power to the engine and the remaining fraction to the ISG or BISG. Vehicle system controller  255  requests the engine power from engine controller  12  and the ISG power from electric machine controller  252 . If the ISG power plus the engine power is less than a transmission input power limit (e.g., a threshold value not to be exceeded), the power is delivered to torque converter  206  which then relays at least a fraction of the requested power to transmission input shaft  270 . Transmission controller  254  selectively locks torque converter clutch  212  and engages gears via gear clutches  211  in response to shift schedules and TCC lockup schedules that may be based on input shaft power and vehicle speed. In some conditions when it may be desired to charge electric energy storage device  275 , a charging power (e.g., a negative ISG power) may be requested while a non-zero driver demand power is present. Vehicle system controller  255  may request increased engine power to overcome the charging power to meet the driver demand power. 
     In response to a request to decelerate vehicle  225  and provide regenerative braking, vehicle system controller may provide a negative desired wheel power (e.g., desired or requested powertrain wheel power) based on vehicle speed and brake pedal position. Vehicle system controller  255  then allocates a fraction of the negative desired wheel power to the ISG  240  and the engine  10 . Vehicle system controller may also allocate a portion of the requested braking power to friction brakes  218  (e.g., desired friction brake wheel power). Further, vehicle system controller may notify transmission controller  254  that the vehicle is in regenerative braking mode so that transmission controller  254  shifts gears  211  based on a unique shifting schedule to increase regeneration efficiency. Engine  10  and ISG  240  may supply a negative power to transmission input shaft  270 , but negative power provided by ISG  240  and engine  10  may be limited by transmission controller  254  which outputs a transmission input shaft negative power limit (e.g., not to be exceeded threshold value). Further, negative power of ISG  240  may be limited (e.g., constrained to less than a threshold negative threshold power) based on operating conditions of electric energy storage device  275 , by vehicle system controller  255 , or electric machine controller  252 . Any portion of desired negative wheel power that may not be provided by ISG  240  because of transmission or ISG limits may be allocated to engine  10  and/or friction brakes  218  so that the desired wheel power is provided by a combination of negative power (e.g., power absorbed) via friction brakes  218 , engine  10 , and ISG  240 . 
     Accordingly, power control of the various powertrain components may be supervised by vehicle system controller  255  with local power control for the engine  10 , transmission  208 , electric machine  240 , and brakes  218  provided via engine controller  12 , electric machine controller  252 , transmission controller  254 , and brake controller  250 . 
     As one example, an engine power output may be controlled by adjusting 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, controller  12  may control the engine power output by controlling a combination of fuel pulse width, fuel pulse timing, and air charge. Engine braking power or negative engine power may be provided by rotating the engine with the engine generating power that is insufficient to rotate the engine. Thus, the engine may generate a braking power via operating at a low power while combusting fuel, with one or more cylinders deactivated (e.g., not combusting fuel), or with all cylinders deactivated and while rotating the engine. The amount of engine braking power may be adjusted via adjusting engine valve timing. Engine valve timing may be adjusted to increase or decrease engine compression work. Further, engine valve timing may be adjusted to increase or decrease engine expansion work. In all cases, engine control may be performed on a cylinder-by-cylinder basis to control the engine power output. 
     Electric machine controller  252  may control power output and electrical energy production from ISG  240  by adjusting current flowing to and from field and/or armature windings of ISG as is known in the art. 
     Transmission controller  254  receives transmission input shaft position via position sensor  271 . Transmission controller  254  may convert transmission input shaft position into input shaft speed via differentiating a signal from position sensor  271  or counting a number of known angular distance pulses over a predetermined time interval. Transmission controller  254  may receive transmission output shaft torque from torque sensor  272 . Alternatively, sensor  272  may be a position sensor or torque and position sensors. If sensor  272  is a position sensor, controller  254  may count shaft position pulses over a predetermined time interval to determine transmission output shaft velocity. Transmission controller  254  may also differentiate transmission output shaft velocity to determine transmission output shaft acceleration. Transmission controller  254 , engine controller  12 , and vehicle system controller  255 , may also receive addition transmission information from sensors  277 , which may include but are not limited to pump output line pressure sensors, transmission hydraulic pressure sensors (e.g., gear clutch fluid pressure sensors), ISG temperature sensors, and BISG temperatures, gear shift lever sensors, and ambient temperature sensors. Transmission controller  254  may also receive requested gear input from gear shift selector  290  (e.g., a human/machine interface device). Gear shift lever may include positions for gears  1 -N (where N is the an upper gear number), D (drive), and P (park). 
     Brake controller  250  receives wheel speed information via wheel speed sensor  221  and braking requests from vehicle system controller  255 . Brake controller  250  may also receive brake pedal position information from brake pedal sensor  154  shown in  FIG.  1    directly or over CAN  299 . Brake controller  250  may provide braking responsive to a wheel power command from vehicle system controller  255 . Brake controller  250  may also provide anti-lock and vehicle stability braking to improve vehicle braking and stability. As such, brake controller  250  may provide a wheel power limit (e.g., a threshold negative wheel power not to be exceeded) to the vehicle system controller  255  so that negative ISG power does not cause the wheel power limit to be exceeded. For example, if controller  250  issues a negative wheel power limit of 50 N-m, ISG power is adjusted to provide less than 50 N-m (e.g., 49 N-m) of negative power at the wheels, including accounting for transmission gearing. 
     Thus, the system of  FIGS.  1  and  2    provides for a system, comprising: an engine including an exhaust system with an exhaust tuning valve; and a controller including executable instructions stored in non-transitory memory that cause the controller to rotate the engine from a position where the engine is not rotating in response to an ambient temperature being within a threshold temperature at which water freezes. The system further comprises additional instructions to adjust a position of the exhaust tuning valve in response to the ambient temperature being within the threshold temperature at which water freezes. The system further comprises additional instructions to adjust the position of the exhaust tuning valve in further response to an ambient humidity. The system further comprises additional instructions to adjust a minimum opening amount of the exhaust tuning valve in response to the ambient temperature. The system further comprises a circuit to activate the controller in response to the ambient temperature and an ambient humidity. The system includes where the circuit includes a humidity sensor and a temperature sensor. The system includes where the circuit includes two comparators. The system includes where the engine is rotated whether or not a vehicle in which the engine resides is activated or deactivated. 
     Referring now to  FIG.  3   , an example vehicle operating sequence according to the method of  FIG.  4    is shown. The operating sequence may be performed via the system of  FIGS.  1  and  2    in cooperation with the method of  FIG.  4   . Vertical lines at times t0-t6 represent times of interest during the sequence. The plots of  FIG.  3    are time aligned. 
     The first plot from the top of  FIG.  3    is a plot of ambient temperature versus time. The vertical axis represents ambient temperature and ambient temperature increases in the direction of the vertical axis arrow. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. Solid line  302  represents ambient temperature. Horizontal line  352  represents a temperature at which water freezes (e.g., 0° C.). Horizontal line  350  represents a temperature that is within a threshold temperature (e.g., 3° C.) of the temperature that is represented by horizontal line  352 . 
     The second plot from the top of  FIG.  3    is a plot of ambient relative humidity versus time. The vertical axis represents percentage of ambient relative humidity (e.g., 0-100%) and the amount of ambient relative humidity increases in the direction of the vertical axis arrow. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. Solid line  304  represents an amount of ambient relative humidity. Horizontal line  454  represents a threshold relative ambient humidity. 
     The third plot from the top of  FIG.  3    is a plot of a vehicle operating state versus time. The vertical axis represents the vehicle operating state and the vehicle is on (e.g., one or more propulsion devices are activated and deliver propulsive effort on demand) when trace  306  is at a higher level near the vertical axis arrow. The vehicle is off and is not prepared to deliver propulsive effort when trace  306  is at a lower level that is near the horizontal axis. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. Trace  306  represents the vehicle operating state. 
     The fourth plot from the top of  FIG.  3    is a plot of engine operating state versus time. The vertical axis represents the engine operating state and the engine is on (e.g., rotating and combusting fuel) when trace  308  is at a higher level near the vertical axis arrow. The engine is off (e.g., not combusting fuel) when trace  308  is at a lower level near the horizontal axis. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. Trace  308  represents the engine operating state. 
     The fifth plot from the top of  FIG.  3    is a plot of exhaust tuning valve positon versus time. The exhaust tuning valve is fully open when trace  310  is at the level of the label FO along the vertical axis. The exhaust valve is fully closed when trace  310  is at the level of the label FC along the vertical axis. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. Trace  310  represents the position of the exhaust tuning valve. 
     The sixth plot from the top of  FIG.  3    is a plot of engine rotation state versus time. The vertical axis represents the engine rotation operating state and the engine is rotating when trace  312  is at a higher level near the vertical axis arrow. The engine is not rotating when trace  312  is at a lower level near the horizontal axis. The horizontal axis represents time and time increases from the left side of the figure to the right side of the figure. Trace  312  represents the engine rotation operating state. 
     At time t0, the ambient temperature is greater than threshold  350  and the ambient humidity is greater than threshold  304 . The vehicle is activated and the engine is on and rotating. The exhaust tuning valve is fully closed. The ambient temperature falls between time t0 and time t1. 
     At time t1, the ambient temperature is less than threshold  350  and greater than threshold  352 . Thus, the ambient temperature is within a threshold temperature of a temperature at which water freezes. The ambient humidity is unchanged. Such conditions may be indicative of water condensing and freezing the exhaust tuning valve to the exhaust system. Therefore, the exhaust tuning valve is commanded open in response to the ambient temperature and ambient humidity. The opening amount of the exhaust tuning valve may be a function of ambient temperature and the vehicle operating state. In this example, the exhaust tuning valve is opened partially (e.g., 10% of full scale) so that exhaust noise may be less pronounced as compared to if the exhaust valve were fully opened. In addition, the minimum opening amount of the exhaust tuning valve is increased so that the exhaust tuning valve remains partially open. Leaving the exhaust valve partially open may reduce the possibility of the exhaust tuning valve freezing and may make it easier to open the exhaust tuning valve if the exhaust tuning valve does freeze. The engine is operating and it continues to rotate. 
     At time t2, the ambient temperature is reduced to a level that is below threshold  352 . Therefore, the exhaust tuning valve is again partially opened and closed to the exhaust tuning valve closing limit. The ambient humidity is unchanged and the vehicle continues to operate. The engine is on and the engine continues to rotate. 
     At time t3, the engine is stopped and it stops rotating shortly thereafter. The vehicle remains activated and the ambient temperature is less than threshold  352 . The ambient humidity is unchanged and the exhaust tuning valve opening amount is positioned at the minimum opening limit. The vehicle state changes from active or on to off between time t3 and time t4. 
     At time t4, the ambient temperature has increase to a level that is above threshold  350 . The ambient humidity is unchanged and the vehicle is reactivated. The engine is also restarted at time t4 and the exhaust tuning valve is held at its minimum opening amount. The engine&#39;s exhaust tuning valve is returned to its fully closed position and the engine rotates as it is started. 
     Between time t4 and time t5, the engine is stopped and it stops rotating. Ambient temperature remains above threshold  350  and ambient humidity is unchanged. The exhaust tuning valve remains fully closed. 
     At time t5, the vehicle is deactivated and the ambient temperature remains above threshold  350 . The ambient humidity is unchanged and the engine is off and not rotating. The exhaust tuning valve is fully closed. 
     At time t6, the ambient temperature falls below threshold  350  while the ambient humidity is unchanged. The lower ambient temperature causes the vehicle&#39;s controller (not shown) to activate and open the exhaust tuning valve. In addition, the engine is rotated via an electric machine (e.g.,  240  of  FIG.  2   ). The engine is rotated so that residual heat in the engine and exhaust system may be utilized to remove water from near the exhaust tuning valve if water is near the valve. The exhaust tuning valve is opened and closed twice. The exhaust tuning valve opening amount may be a function of ambient temperature and vehicle operating state. For example, the exhaust tuning valve may be commanded to a more open position when the engine is not on as compared to when the engine is off so as to mitigate increasing exhaust noise. Further, the exhaust tuning valve may be opened more at lower ambient temperatures as compared to opening the exhaust tuning valve a warmer temperatures. The exhaust tuning valve is also maintained at a position that is greater than a minimum exhaust tuning valve opening amount. The engine rotation is stopped and the exhaust tuning valve is moved to its minimum opening position shortly after time t5. 
     In this way, a position of an exhaust tuning valve may be adjusted to reduce a possibility of a stuck valve. By moving the exhaust tuning valve, ice that may be forming on the valve may be broke so that the exhaust tuning valve may move freely. In addition, the exhaust tuning valve may be held partially open at a minimum exhaust tuning valve opening amount so that there may be less opportunity for ice to attach the exhaust tuning valve to the exhaust system. 
     Referring now to  FIG.  4   , a flow chart of a method for operating an engine with an exhaust tuning valve is shown. The method of  FIG.  4    may be incorporated into and may cooperate with the system of  FIGS.  1  and  2   . Further, at least portions of the method of  FIG.  4    may be incorporated as executable instructions stored in non-transitory memory while other portions of the method may be performed via a controller transforming operating states of devices and actuators in the physical world. 
     At  402 , method  400  determines vehicle operating conditions. Vehicle operating conditions may include but are not limited to engine speed, ambient temperature, ambient humidity, vehicle speed, engine temperature, engine load, and driver demand torque or power. Method  400  proceeds to  404 . 
     At  404 , method  400  judges if present ambient temperature is within a threshold temperature range of a temperature at which water freezes and if present ambient humidity is greater than a threshold humidity. For example, if the ambient temperature threshold is 3° C. and present ambient temperature is 2° C., then the present ambient temperature is within the threshold temperature at which water freezes 0° C. If present ambient relative humidity is 50% and the humidity threshold is 45% relative humidity, then the present ambient relative humidity is greater than the humidity threshold. If method  400  judges that ambient temperature is within a threshold temperature range of a temperature at which water freezes and if present ambient humidity is greater than a threshold humidity, the answer is yes and method  400  proceeds to  406 . Otherwise, the answer is no and method  400  proceeds to exit. In one example, the conditions of  404  may be determined via the circuit shown in  FIG.  5   . The circuit of  FIG.  5    may cause the vehicle controller  12  to wake from a sleep (e.g., low activity state) to perform the actions that are described herein. 
     At  406 , method  400  judges if the vehicle that includes the exhaust tuning valve is activated. The vehicle may be activated when one or more of the vehicle&#39;s propulsion devices is prepared to respond to driver demand input. If method  400  judges that the vehicle is activated, the answer is yes and method  400  proceeds to  420 . Otherwise, the answer is no and method  400  proceeds to  408 . 
     At  408 , method  400  may rotate the vehicle&#39;s engine via an electric machine (e.g.,  240  of  FIG.  2  or  96    of  FIG.  1   ). In one example, method  400  may rotate the engine if it is determined that there is heat in the engine or exhaust system that may aid in evaporation of water that may be near the exhaust tuning valve. Method  400  may judge if there is heat in the engine and exhaust system via a temperature sensor. The engine may be rotated without supplying fuel to the engine, thereby pumping warmed air to the engine with exhaust that may contain fewer hydrocarbons. Method  400  proceeds to  410 . 
     At  410 , method  400  cycles the exhaust tuning valve from a first position (more closed) to a second position (more open). The exhaust tuning valve may be cycled a plurality of times so that water that may be near crystalizing may be removed from the exhaust tuning valve. In addition, the exhaust tuning valve&#39;s minimum opening position (e.g., a minimum amount that the exhaust tuning valve has to stay open) may be increased so that the exhaust tuning valve does not fully close. For example, during nominal operating conditions the exhaust tuning valve may fully close when the valve&#39;s minimum opening position is small. However, the exhaust tuning valve may be held 10% open when ambient temperature is near a temperature at which water may freeze. Method  400  proceeds to exit. 
     At  420 , method  400  judges if the vehicle&#39;s engine is running (e.g., rotating and combusting fuel). If so, the answer is yes and method  400  proceeds to  426 . Otherwise, the answer is no and method  400  proceeds to  422 . 
     At  422 , method  400  judges if the engine and/or exhaust system are warm. In one example, method  400  may judge if the engine temperature is greater than a threshold temperature. If so, the answer is yes and method  400  proceeds to  424 . Otherwise, the answer is no and method  400  proceeds to  426 . Method  400  may determine whether or not the engine is warm so that it may be established if there is sufficient heat in the engine and exhaust system to warm water that may be in the exhaust system. 
     At  424 , method  400  may rotate the vehicle&#39;s engine via an electric machine (e.g.,  240  of  FIG.  2  or  96    of  FIG.  1   ). The engine may be rotated without supplying fuel to the engine, thereby pumping warmed air to the engine with exhaust that may contain fewer hydrocarbons. Method  400  proceeds to  426 . 
     At  426 , method  400  cycles the exhaust tuning valve from a first position (more closed) to a second position (more open). The exhaust tuning valve may be cycled a plurality of times so that water that may be near crystalizing may be removed from the exhaust tuning valve. In addition, the exhaust tuning valve&#39;s minimum opening position (e.g., a minimum amount that the exhaust tuning valve has to stay open) may be increased so that the exhaust tuning valve does not fully close. Method  400  proceeds to exit. 
     In this way, a position of an exhaust tuning valve may be adjusted before a present ambient temperature is reduced to a temperature at which water may freeze. As such, preemptive clearing of the exhaust tuning valve may be possible so that water may be removed from the exhaust tuning valve. In addition, if water does freeze near the exhaust tuning valve, there may be less ice to remove if the water freezes since moving the exhaust tuning valve may cause water to shed from the valve. Further, a minimum opening position of the exhaust tuning valve may be increased so that water may have to span a further distance to cause the exhaust tuning valve to stick. 
     Thus, the method of  FIG.  4    provides for a method for operating an engine, comprising: adjusting a position of a valve in an exhaust system of the engine via a controller in response to ambient temperature being within a threshold temperature of a temperature at which water freezes and ambient relative humidity being greater than a threshold relative humidity. The method includes where the threshold relative humidity is greater than 50% relative humidity. The method further comprises increasing a minimum opening amount of the valve in response to the ambient temperature being within a threshold temperature of the temperature at which water freezes. The method further comprises decreasing the minimum opening amount of the valve in response to the ambient temperature being greater than the threshold temperature plus the temperature at which water freezes. The method includes where adjusting the position of the valve includes commanding the valve to cycle from a more closed position to a more open position. The method further comprises rotating the engine from a position where the engine is not rotating in response to the ambient temperature being within the threshold temperature of the temperature at which water freezes and ambient humidity being greater than the threshold humidity. The method includes where the a vehicle in which the engine resides is not activated when the engine is at the position where the engine is not rotating. 
     The method of  FIG.  4    also provides for a method for operating an engine, comprising: adjusting a position of a valve in an exhaust system of the engine via a controller in response to an ambient temperature being within a threshold temperature of a temperature at which water freezes, where adjusting the position includes increasing a minimum opening amount of the valve. The method further comprises rotating the engine in response to the ambient temperature being within the threshold temperature of the temperature at which water freezes. The method includes where adjusting the position includes cycling the valve from a first position to a second position, where the first position is more closed than the second position. The method further comprises varying a commanded opening amount of the valve in response to the ambient temperature. The method further comprises varying a commanded opening amount of the valve in response to an ambient humidity. 
     Referring now to  FIG.  5   , a schematic diagram of an example circuit for waking a controller  12  that is in a sleeping mode (e.g., low energy consumption mode with limited capability) is shown. The circuit includes a first comparator  520  and a second comparator  522 . The first comparator  520  receives a voltage output of temperature sensor  170 , which is indicative of ambient temperature, at its positive terminal, which is denoted “+.” The first comparator  520  also receives a voltage output of a voltage divider circuit  510  that is indicative of a voltage at which water may freeze plus an offset temperature or temperature range (e.g., 0.5 volts=0° C.+2° C.) at its negative terminal, which is denoted “−.” First comparator  520  outputs a value that is equal to logical 1 when a voltage at its positive terminal is greater than a voltage that is at its negative terminal. First comparator  520  outputs a value that is equal to logical 0 when a voltage at its positive terminal is less than a voltage that is at its negative terminal. Therefore, whenever ambient temperature is less than 0° C. plus an offset temperature or a threshold temperature range, first comparator outputs a logical zero. 
     The second comparator  522  receives a voltage output of humidity sensor  172 , which is indicative of ambient temperature, at its negative terminal, which is denoted “−.” The second comparator  522  also receives a voltage output of a voltage divider circuit  512  that is indicative of a voltage that is output by the humidity sensor at a particular humidity or relative humidity level (e.g., 50% relative humidity) at its positive terminal, which is denoted “+.” Second comparator  522  outputs a value that is equal to logical 1 when a voltage at its positive terminal is greater than a voltage that is at its negative terminal. Second comparator  522  outputs a value that is equal to a logical 0 when a voltage at its positive terminal is less than a voltage that is at its negative terminal. Therefore, whenever ambient humidity is greater than the humidity level that is represented by the voltage that is output of voltage divider  512 , second comparator  522  outputs a logical zero. 
     The output of first comparator  520  and the output of second comparator  522  are input to AND gate  514 . The AND gate  514  outputs a logical zero and it pulls the voltage that is input to controller  12  down to ground level when ambient temperature is less than a temperature at which water freezes plus an offset or threshold temperature and when ambient humidity is greater than a threshold humidity. The controller  12  may be waked from a sleep state when it receives a low level input. The controller may open and close the exhaust tuning throttle in response to being awakened. In addition, the controller may rotate an engine without fueling the engine via an electric machine in response to being awakened. 
     Note that the example control and estimation routines included herein can be used with various engine and/or vehicle system configurations. The control methods and routines disclosed herein may be stored as executable instructions in non-transitory memory and may be carried out by the control system including the controller in combination with the various sensors, actuators, and other engine hardware. The specific routines described herein may represent one or more of any number of processing strategies such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. As such, various actions, operations, and/or functions illustrated may be performed in the sequence illustrated, in parallel, or in some cases omitted. Likewise, the order of processing is not necessarily required to achieve the features and advantages of the example embodiments described herein, but is provided for ease of illustration and description. One or more of the illustrated actions, operations and/or functions may be repeatedly performed depending on the particular strategy being used. Further, at least a portion of the described actions, operations and/or functions may graphically represent code to be programmed into non-transitory memory of the computer readable storage medium in the control system. The control actions may also transform the operating state of one or more sensors or actuators in the physical world when the described actions are carried out by executing the instructions in a system including the various engine hardware components in combination with one or more controllers. 
     This concludes the description. The reading of it by those skilled in the art would bring to mind many alterations and modifications without departing from the spirit and the scope of the description. For example, single cylinder, I3, I4, I5, V6, V8, V10, and V12 engines operating in natural gas, gasoline, diesel, or alternative fuel configurations could use the present description to advantage.