Patent Publication Number: US-11649795-B2

Title: Methods and system for inhibiting automatic engine stopping

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application is a divisional of U.S. Non-Provisional patent application Ser. No. 16/983,213, entitled “METHODS AND SYSTEM FOR INHIBITING AUTOMATIC ENGINE STOPPING”, and filed on Aug. 3, 2020. The entire contents of the above-listed application are hereby incorporated by reference for all purposes. 
    
    
     FIELD 
     The present description relates to methods and a system for determining inhibiting of automatic engine pull-downs. The methods and systems may be suitable for vehicles that include more than one engine starting device. 
     BACKGROUND AND SUMMARY 
     An engine of a vehicle may be pulled-down (e.g., engine rotational speed reduced to zero and no combustion within the engine) to conserve fuel during driving of the vehicle. The engine may be pulled-up or started after the pull-down to provide propulsive force so that vehicle occupants may reach their intended destination. However, if an engine starting device is applied to start the engine more than may be expected, the vehicle may have to be serviced sooner than may be expected. 
     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 
         FIG.  1    shows a schematic diagram of an internal combustion engine; 
         FIG.  2    shows a schematic diagram of an example vehicle driveline or powertrain including the internal combustion engine shown in  FIG.  1   ; 
         FIGS.  3 A and  3 B  show an example block diagram of a method for determining availability of an engine starting device to start the engine; and 
         FIG.  4    shows an example vehicle operating sequence according to the method of  FIG.  4   . 
     
    
    
     DETAILED DESCRIPTION 
     The present description is related to controlling inhibiting of engine pull-down to ensure that an engine starting device may be operational for its expected lifespan. The inhibiting of engine pull-down may be applied to an engine of the type shown in  FIG.  1   . The engine may be included in a driveline as shown in  FIG.  2   . The driveline may include more than one engine starting device. In one example, a conventional starter and a belt integrated starter/generator (BISG) are included in a driveline for starting an engine. Inhibiting of engine pull-down may be based on operating characteristics of an engine starting device including distance traveled by a vehicle and a cumulative total number of engine starts since a starting device was installed in the vehicle. The inhibiting of engine pull-down may be determined as shown in the block diagram of  FIGS.  3 A and  3 B . An example vehicle operating sequence according to the method of  FIGS.  3 A and  3 B  is shown in  FIG.  4   . 
     An engine of a vehicle that has been pulled-down to zero speed such that the engine&#39;s rotational speed is stopped may help to conserve fuel during a vehicle drive cycle. After the engine pull-down, the engine may be restarted by one of a plurality of engine starting devices that may be included with a vehicle. However, if one of the plurality of engine starting devices is used to start the engine more frequently than may be expected, the one engine starting device may exhibit a shorter lifespan (often described in terms of distance travelled) than may be expected. Consequently, the vehicle may need to be serviced sooner than may be expected or desired. 
     The inventors herein have recognized the above-mentioned issues and have developed a method for operating a vehicle, comprising: inhibiting an automatic engine pull-down via a controller based on a minimum engine running time for enabling automatic engine pull-down and based on a minimum vehicle travel distance for enabling automatic engine pull-down. 
     By inhibiting engine pull-down based on a minimum engine running time for enabling automatic engine pull-down and based on a minimum vehicle travel distance for enabling automatic engine pull-down, it may be possible to control an actual total number of engine starts generated via an engine starting device over a distanced travelled by the vehicle. In particular, if an error based on a ratio of an actual total number of engine starts since installation of an engine starting device into a vehicle to an actual total distance traveled by a vehicle since installation of the engine starting device is positive, then a minimum engine run time to enable engine pull-down may be increased so that fewer automatic engine stops and starts may be generated. Conversely, if the error based on the ratio of the actual total number of engine starts since installation of the engine starting device into the vehicle to the actual total distance traveled by the vehicle since installation of the engine starting device is negative, then a minimum engine run time to enable engine pull-down may be decreased so that additional automatic engine stops and starts may be generated to conserve fuel. 
     The present description may provide several advantages. Specifically, the approach may adjust automatic engine pull-ups and pull-downs such that an engine starting device may reach a desired lifespan or duration relative to vehicle distance travelled. Further, the approach may respond to an actual total number of engine starts that may be generated via a particular engine starting device and an actual total distance that a vehicle has traveled since the engine starting device was installed in a vehicle so that the engine starting device lifespan may reach vehicle distance criteria and a number of engine starts criteria. In addition, the approach may reduce a possibility of the engine starting device being replaced sooner than may be expected. 
     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. 
     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 . 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 . Starter  96  (e.g., low voltage (operated with less than 20 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 torque 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 poppet valve  52  and exhaust poppet 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 . A lift amount and/or a phase or position of intake valve  52  may be adjusted relative to a position of crankshaft  40  via valve adjustment device  59 . A lift amount and/or a phase or position of exhaust valve  54  may be adjusted relative to a position of crankshaft  40  via valve adjustment device  58 . Valve adjustment devices  58  and  59  may be electro-mechanical devices, hydraulic devices, or mechanical devices. 
     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. Fuel injector  66  delivers liquid fuel in proportion to the pulse width from controller  12 . Fuel is delivered to fuel injector  66  by a fuel system (not shown) including a fuel tank, fuel pump, and fuel rail (not shown). In one example, a high pressure, dual stage, fuel system may be used to generate higher fuel pressures. 
     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 . Universal Exhaust Gas Oxygen (UEGO) sensor  126  is shown coupled to exhaust manifold  48  upstream of catalytic converter  70 . Alternatively, a two-state exhaust gas oxygen sensor may be substituted for UEGO sensor  126 . 
     Converter  70  can include multiple catalyst bricks, in one example. In another example, multiple emission control devices, each with multiple bricks, can be used. Converter  70  can be a three-way type catalyst in one example. 
     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: cylinder head temperature from temperature sensor  112  coupled to cylinder head  35 ; a position sensor  134  coupled to an propulsion pedal  130  for sensing force applied by human foot  132 ; a position sensor  154  coupled to brake pedal  150  for sensing force applied by foot  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 ; 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. 
     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 torque 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 propulsion 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 speed change. 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 increase speed of the driveline and wheel rotation. 
     Vehicle controller  255  and/or engine controller  12  may also receive input from human/machine interface  256  and traffic conditions (e.g., traffic signal status, distance to objects, etc.) from sensors  257  (e.g., cameras, LIDAR, RADAR, etc.). In one example, human/machine interface  256  may be a touch input display panel. Alternatively, human/machine interface  256  may be a key switch or other known type of human/machine interface. Human/machine interface  256  may receive requests from a user. For example, a user may request an engine stop or start via human/machine interface  256 . Additionally, human/machine interface  256  may display status messages and engine data that may be received from controller  255 . 
     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  (e.g., ISG). In other examples, engine  10  may be omitted. Engine  10  may be started with an engine starting system shown in  FIG.  1   , via belt integrated starter/generator BISG  219 , or via driveline integrated starter/generator (ISG)  240  also known as an integrated starter/generator. A temperature of BISG windings may be determined via BISG winding temperature 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 torque actuator  204 , such as a fuel injector, throttle, etc. 
     BISG  219  is mechanically coupled to engine  10  via belt  231  and BISG  219  may be referred to as an electric machine, motor, or generator. BISG  219  may be coupled to crankshaft  40  or a camshaft (e.g.,  51  or  53  of  FIG.  1   ). BISG  219  may operate as a motor when supplied with electrical power via high voltage bus  274  via inverter  217 . Inverter  217  converts direct current (DC) power from high voltage bus  274  to alternating current (AC) and vice-versa so that power may be exchanged between BISG  219  and electric energy storage device  275 . Thus, BISG  219  may operate as a generator supplying electrical power to high voltage electric energy storage device (e.g., battery)  275  and/or low voltage bus  273 . Bi-directional DC/DC converter  281  may transfer electrical energy from a high voltage buss  274  to a low voltage bus  273  or vice-versa. Low voltage battery  280  is electrically directly coupled to low voltage bus  273 . Low voltage bus  273  may be comprised of one or more electrical conductors. Electric energy storage device  275  is electrically coupled to high voltage bus  274 . Low voltage battery  280  may selectively supply electrical energy to starter motor  96 . 
     An engine output power may be transmitted to a first or upstream side of powertrain disconnect clutch  235  through dual mass flywheel  215 . Disconnect clutch  236  is hydraulically actuated and hydraulic pressure within driveline disconnect clutch  236  (driveline disconnect clutch pressure) may be adjusted via electrically operated valve  233 . The downstream or second side  234  of disconnect clutch  236  is shown mechanically coupled to ISG input shaft  237 . 
     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. ISG  240  is in electrical communication with energy storage device  275  via inverter  279 . Inverter  279  may convert direct current (DC) electric power from electric energy storage device  275  into alternating current (AC) electric power for operating ISG  240 . Alternatively, inverter  279  may convert AC power from ISG  240  into DC power for storing in electric energy storage device  275 . Inverter  279  may be controlled via electric machine controller  252 . 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  212  is locked. TCC  212  is electrically operated by controller  254 . Alternatively, TCC may be hydraulically locked. In one example, the torque converter  206  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 torque 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 that is directly delivered 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  211  and forward clutch  210  for selectively engaging and disengaging forward gears  213  (e.g., gears 1-10) and reverse gear  214 . 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 transferred 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. 
     In response to a request to increase speed of vehicle  225 , vehicle system controller may obtain a driver demand power or power request from an propulsion 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. 
     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  240  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 speed change. 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 selector  290  may include positions for gears  1 -X (where X is an upper gear number), D (drive), neutral (N), and P (park). Shift selector  290  shift lever  293  may be prevented from moving via a solenoid actuator  291  that selectively prevents shift lever  293  from moving from park or neutral into reverse or a forward gear position (e.g., drive). 
     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 torque limit of 50 N-m, ISG power is adjusted to provide less than 50 N-m (e.g., 49 N-m) of negative torque at the wheels, including compensating for transmission gearing. 
     The system of  FIGS.  1  and  2    provides for a vehicle system, comprising: an internal combustion engine; a plurality of engine starting devices; and a controller including executable instructions stored in non-transitory memory that cause the controller to inhibit automatic stopping of the internal combustion engine based on a ratio of an actual total number of engine starts generated via an engine starting device and an actual total distance traveled by a vehicle since the engine starting device was installed in the vehicle. The vehicle system includes where the actual total number of engine starts generated by the engine starting device begin when the engine starting device was installed in the vehicle. The vehicle system further comprises additional instructions to generate an error from the ratio of the actual total number of engine starts generated via the engine starting device and the actual total distance traveled by the vehicle since the engine starting device was installed in the vehicle. The vehicle system further comprises additional instructions to integrate the error. The vehicle system further comprises additional instructions to rate limit the error. The vehicle system further comprises additional instructions to low pass filter the error. The vehicle system further comprises additional instructions to start the internal combustion engine via one of the plurality of engine starting devices. The vehicle system further comprises additional instructions to determine a total number of engine starts generated via one of the plurality of engine starting devices since the one of the plurality of engine starting devices was installed in the vehicle. 
     Referring now to  FIGS.  3 A and  3 B , a block diagram  300  of a method to control inhibiting of automatic engine stopping (e.g., an engine stop that is requested via a controller without input via a human to a dedicated device that has a sole purpose of starting/stopping an engine, such as a key switch, pushbutton, or display) based, at least in part, on operating conditions of an engine starting device is shown. Since block diagram  300  controls automatic engine stopping, it also controls whether or not an engine may be automatically restarted. For example, if block diagram  300  prevents automatic engine stopping, it prevents automatic engine starting since the engine may not be automatically started without being automatically stopped. The block diagram may be implemented as executable instructions in one or more of the controllers shown in  FIGS.  1  and  2   . Herein, block diagram  300  is described according to block  300  being based on a starting device that is a BISG. However, the method of block diagram  300  may be applied to a conventional starter (e.g.,  96  of  FIG.  1   ) and/or an ISG (e.g.,  240  of  FIG.  2   ). In addition, similar block diagrams for describing control of inhibiting automatic engine stopping based on other engine starting devices may be generated. At least portions of block diagram  300  may be implemented as executable controller instructions stored in non-transitory memory. In addition, block diagram  300  may operate in cooperation with the system of  FIGS.  1  and  2   . Further, at least portions of the method described by block diagram  300  may be actions taken via a controller in the physical world to transform an operating state of an actuator or device. 
     Block  338  represents the vehicle powertrain control system (e.g., controllers, sensors, and actuators shown in  FIG.  2   ) and the vehicle powertrain control system determines an amount of time since the engine was most recently running (e.g., rotating and combusting fuel) and outputs the amount of time at output  318   a . For example, if an engine is started at time t 0 , the present time is t 1 , and the amount of time between t 0  and time t 1  is two minutes, then block  338  outputs a value of two minutes at output  338   a , which is input to block  310 . Block  338  also outputs an actual total number of engine starts since the engine starting device (BISG) was installed in the vehicle. For example, if the BISG was installed at time of vehicle manufacture and the engine has started a total of 1000 times since the BISG was installed in the vehicle, then block  338  outputs a value of 1000 at output  338   b . Thus, the actual total number of engine starts begins with the first engine start generated by the engine starting device immediately following installation of the engine starting device into the vehicle. Block  338  also outputs a total distance that the vehicle (e.g., vehicle  225  of  FIG.  2   ) has traveled since the engine starting device (BISG) was installed in the vehicle. For example, if the BISG was installed at time of vehicle manufacture and the vehicle has traveled an actual total of 10,000 kilometers since the BISG was installed in the vehicle, then block  338  outputs a value of 10,000 kilometers at output  338   c . Block  338  also outputs a distance traveled by the vehicle since the engine was most recently started and began running continuously (e.g., without stopping). For example, if the engine started running most recently with a total distance traveled since vehicle manufacture of 20,000 kilometers and the vehicle&#39;s present distance traveled is 20,100 kilometers with no engine stopping (e.g., no stopping of engine rotation) between the 20,000 kilometers and the 20,100 kilometers, then block  338  outputs a value of 100 kilometers at output  338   d.    
     Block  340  receives the output of  338   b  and  338   c  and it outputs a cumulative actual total number of engine starts per unit distance traveled by the vehicle since the engine starting device (BISG) was installed in the vehicle at output  340   a . Block  340  arrives at the cumulative actual total number of engine starts per unit distance by dividing the actual total number of engine starts since the engine starting device (BISG) was installed in the vehicle by the total distance that the vehicle has traveled since the engine starting device (BISG) was installed in the vehicle. The output  340   a  is input to summing junction  342 . 
     At summing junction  342 , a predetermined threshold actual total number of engine starts per unit distance traveled by the vehicle since the engine starting device was installed in the vehicle from block  344  is subtracted from the cumulative actual total number of engine starts per unit distance traveled by the vehicle since the engine starting device (BISG) was installed in the vehicle. Summing junction  342  outputs an error of the cumulative actual total number of engine starts per unit distance traveled by the vehicle since the engine starting device (BISG) was installed in the vehicle to block  346 . The predetermined threshold actual total number of engine starts per unit distance traveled by the vehicle since the engine starting device was installed in the vehicle may be based on a desired level of durability for the engine starting device (BISG). 
     Block  346  smooths the output of summing junction  342 . In one example, block  346  may integrate the output of summing junction  342 . In another example, block  346  may low pass filter output of summing junction  342  via a first order low pass filter. In still another example, block  346  may rate limit output of summing junction  342 . For example, block  346  may only allow a maximum rate of change of 0.5 engine starts per kilometer traveled. Block  346  outputs a smoothed output of summing junction  342  at output  346   a  to blocks  302 ,  304 ,  308 ,  312 ,  316 , and  320 . 
     At block  302 , block diagram  300  outputs other requests for engine pull-ups (e.g., engine starts) and engine pull-downs. For example, an automatic engine pull-down request may be generated when a vehicle is not moving for a threshold amount of time and the vehicle&#39;s brake pedal is applied. Further, an engine pull-down request may be generated when a human vehicle operator specifically requests an engine stop via a dedicated input that has a sole function of requesting engine stops and starts (e.g., a pushbutton, key switch, or display panel). Block  302  outputs other engine pull-up and pull-down requests at output  302   a  to block  332 . 
     At block  304 , block diagram  300  determines a minimum vehicle travel distance for continuous engine operation or running for enabling automatic engine pull-down. For example, block  304  may output a value of 10 kilometers when the smoothed error output of block  346  is a value of 0.5 engine starts/kilometer distance traveled by the vehicle. In one example, block diagram  300  indexes or references a table or function that outputs a minimum vehicle travel distance with continuous engine operation for enabling automatic engine pull-down via the smoothed output of block  346  (e.g., smoothed error of cumulative engine starts per unit distance traveled). The values in the table or function may be empirically determined via operating a vehicle and assessing a level of engine starting device degradation as a function of distance traveled by the vehicle. Thus, block  304  outputs an amount of distance at output  304   a . In one example, if the cumulative engine starts per unit distance traveled error has a positive sign, the output of block  304  increases the minimum distance that the vehicle travels with continuous engine operation before automatic engine pull-down is permitted. Conversely, if the cumulative engine starts per unit distance traveled error has a negative sign, the output of block  304  decreases the minimum distance that the vehicle travels with continuous engine operation (e.g., rotating and combusting fuel) before automatic engine pull-down is permitted. 
     At block  306 , block diagram  300  determines if the distance output by block  304  is greater than the time output by block  338 . In other words, block  306  judges if the minimum distance that the vehicle traveled before engine pull-down is permitted is greater than the distance the vehicle has traveled since the most recent engine start. If block  306  judges that the minimum distance of vehicle travel before engine pull-down is permitted is greater than the distance the vehicle has traveled since the most recent engine start the time, then the answer is true and block  306  outputs a logical TRUE value at output  306   a  to block  332 . If block  306  judges that the distance that is output by block  304  is not greater than the output  338   d , then the answer is FALSE and block  306  outputs a logical FALSE value at output  306   a  to block  332 . 
     At block  308 , block diagram  300  determines a minimum amount of time of continuous engine operation (e.g., rotating and combusting fuel) or engine running time for enabling automatic engine pull-down. For example, block  308  may output a value of 10 minutes when the smoothed error output of block  346  is a value of 0.5 engine starts/kilometer distance traveled by the vehicle. In one example, block diagram  300  indexes or references a table or function that outputs a minimum amount of time of continuous engine operation for enabling automatic engine pull-down via the smoothed output of block  346  (e.g., smoothed error of cumulative engine starts per unit distance traveled). The values in the table or function may be empirically determined via operating a vehicle and assessing a level of engine starting device degradation as a function of continuous engine operation. Thus, block  308  outputs an amount of time at output  308   a  to block  310 . In one example, if the cumulative engine starts per unit distance traveled error ( 346   a ) has a positive sign, the output of block  308  increases the minimum amount of time of continuous engine operation before automatic engine pull-down is permitted via calibratable function of the error ( 346   a ). Conversely, if the cumulative engine starts per unit distance traveled error ( 346   a ) has a negative sign, the output of block  308  decreases the minimum amount of time of continuous engine operation (e.g., rotating and combusting fuel) in a calibratable (e.g., adjustable via functions stored in controller memory) manner before automatic engine pull-down is permitted. 
     At block  310 , block diagram  300  determines if the time output by block  308  is greater than the time output by block  338 . In other words, block  310  judges if the minimum time of continuous engine running is greater than the amount of time the engine has continuously been running since the most recent engine start. If block  310  judges that the time that is output by block  308  is greater than the output  338   a , then the answer is true and block  310  outputs a logical TRUE value at output  310   a  to block  332 . If block  310  judges that the time that is output by block  308  is not greater than the output  338   a , then the answer is FALSE and block  310  outputs a logical FALSE value at output  310   a  to block  332 . 
     At block  312 , block diagram  300  determines a minimum driver demand torque (e.g., a wheel torque) to enable automatic engine pull-down. For example, block  312  may output a value of 100 Newton-meters when the smoothed error output of block  346  is a value of 0.5 engine starts/kilometer distance traveled by the vehicle. In one example, block diagram  300  indexes or references a table or function that outputs a minimum driver demand torque for enabling automatic engine pull-down via the smoothed output of block  346  (e.g., smoothed error of cumulative engine starts per unit distance traveled). The values in the table or function may be empirically determined via operating a vehicle and assessing a level of engine starting device degradation as a function of minimum driver demand torque. Thus, block  312  outputs a minimum driver demand torque at output  312   a . In one example, if the cumulative engine starts per unit distance traveled error has a positive sign, the output of block  312  decreases the minimum driver demand torque at which automatic engine pull-down is permitted. Conversely, if the cumulative engine starts per unit distance traveled error has a negative sign, the output of block  312  increases the minimum driver demand torque at which automatic engine pull-down is permitted. 
     At block  314 , block diagram  300  determines if the minimum driver demand torque output by block  312  is less than the driver demand torque (DT). In other words, block  314  judges if the minimum driver demand torque at which engine pull-down is permitted is less than the present driver demand torque. If block  314  judges that the minimum driver demand torque is less than the present driver demand torque, the answer is TRUE and block  314  outputs a logical TRUE value at output  314   a  to block  332 . If block  314  judges that the minimum driver demand torque is not less than the present driver demand torque, the answer is FALSE and block  314  outputs a logical FALSE value at output  314   a  to block  332 . It should be noted that hysteresis may be incorporated into this comparison so that jitter or rapid state changing of the output may be avoided. 
     At block  316 , block diagram  300  determines a minimum driver demand power (e.g., a wheel power) to enable automatic engine pull-down. For example, block  316  may output a value of 1000 Kilowatts when the smoothed error output of block  346  is a value of 0.5 engine starts/kilometer distance traveled by the vehicle. In one example, block diagram  300  indexes or references a table or function that outputs a minimum driver demand power for enabling automatic engine pull-down via the smoothed output of block  346  (e.g., smoothed error of cumulative engine starts per unit distance traveled). The values in the table or function may be empirically determined via operating a vehicle and assessing a level of engine starting device degradation as a function of minimum driver demand power. Thus, block  316  outputs a minimum driver demand power at output  316   a . In one example, if the cumulative engine starts per unit distance traveled error has a positive sign, the output of block  316  decreases the minimum driver demand power at which automatic engine pull-down is permitted. Conversely, if the cumulative engine starts per unit distance traveled error has a negative sign, the output of block  316  increases the minimum driver demand power at which automatic engine pull-down is permitted. 
     At block  318 , block diagram  300  determines if the minimum driver demand power output by block  316  is less than the driver demand power (DP). In other words, block  318  judges if the minimum driver demand power at which engine pull-down is permitted is less than the present driver demand power. If block  318  judges that the minimum driver demand power is less than the present driver demand power, the answer is TRUE and block  318  outputs a logical TRUE value at output  318   a  to block  332 . If block  318  judges that the minimum driver demand torque is not less than the present driver demand torque, the answer is FALSE and block  318  outputs a logical FALSE value at output  318   a  to block  332 . It should be noted that hysteresis may be incorporated into this comparison so that jitter or rapid state changing of the output may be avoided. 
     At block  320 , block diagram  300  determines a minimum battery state of charge (SOC) to enable automatic engine pull-down. For example, block  320  may output a value of 75% when the smoothed error output of block  346  is a value of 0.5 engine starts/kilometer distance traveled by the vehicle. In one example, block diagram  300  indexes or references a table or function that outputs a minimum SOC for enabling automatic engine pull-down via the smoothed output of block  346  (e.g., smoothed error of cumulative engine starts per unit distance traveled). The values in the table or function may be empirically determined via operating a vehicle and assessing a level of engine starting device degradation as a function of SOC at which automatic engine stop is permitted. Thus, block  320  outputs a SOC at output  320   a . In one example, if the cumulative engine starts per unit distance traveled error has a positive sign, the output of block  320  increases the SOC at which automatic engine pull-down is permitted. Conversely, if the cumulative engine starts per unit distance traveled error has a negative sign, the output of block  320  decreases the SOC at which automatic engine pull-down is permitted. 
     At block  322 , block diagram  300  determines if the minimum SOC output by block  320  is less than the present SOC. In other words, block  322  judges if the minimum SOC at which engine pull-down is permitted is greater than the present SOC. If block  322  judges that the minimum SOC is greater than the present SOC, the answer is TRUE and block  322  outputs a logical TRUE value at output  322   a  to block  332 . If block  322  judges that the minimum SOC is not less than the present SOC, the answer is FALSE and block  322  outputs a logical FALSE value at output  314   a  to block  332 . It should be noted that hysteresis may be incorporated into this comparison so that jitter or rapid state changing of the output may be avoided. 
     At block  324 , block diagram  300  determines a maximum vehicle speed to enable automatic engine pull-down. For example, block  312  may output a value of 100 kilometers/hour. In one example, block diagram  300  indexes or references a table or function that outputs a maximum vehicle speed to enable automatic engine pull-down via the smoothed output of block  346  (e.g., smoothed error of cumulative engine starts per unit distance traveled). The values in the memory location may be empirically determined via operating a vehicle and assessing a level of engine starting device degradation as a function of maximum vehicle speed. Thus, block  324  outputs a maximum vehicle speed. 
     At block  326 , block diagram  300  determines if the maximum vehicle speed output by block  324  is less than the present vehicle speed (VS). In other words, block  326  judges if the maximum vehicle speed at which engine pull-down is permitted is less than the present vehicle speed. If block  326  judges that the maximum vehicle speed is less than the present vehicle speed, the answer is TRUE and block  326  outputs a logical TRUE value at output  326   a  to block  332 . If block  326  judges that the maximum vehicle speed is not less than the present vehicle speed, the answer is FALSE and block  326  outputs a logical FALSE value at output  326   a  to block  332 . It should be noted that hysteresis may be incorporated into this comparison so that jitter or rapid state changing of the output may be avoided. 
     At block  328 , block diagram  300  determines a maximum transmission assembly input speed (e.g., input shaft speed) to enable automatic engine pull-down. For example, block  328  may output a value of 3000 RPM. In one example, block diagram  300  indexes or references a table or function that outputs a maximum transmission assembly input speed for enabling automatic engine pull-down via the smoothed output of block  346  (e.g., smoothed error of cumulative engine starts per unit distance traveled). The values in the memory location may be empirically determined via operating a vehicle and assessing a level of engine starting device degradation as a function of maximum vehicle speed. Thus, block  328  outputs a maximum transmission input shaft speed. 
     At block  330 , block diagram  300  determines if the maximum transmission input shaft speed output by block  328  is less than the present transmission input shaft speed (TrnAin). In other words, block  330  judges if the maximum transmission input shaft speed at which engine pull-down is permitted is less than the present transmission input shaft speed. If block  330  judges that the maximum transmission input shaft speed is less than the transmission input shaft speed, the answer is TRUE and block  330  outputs a logical TRUE value at output  330   a  to block  332 . If block  330  judges that the maximum transmission input shaft speed is not less than the present transmission input shaft speed, the answer is FALSE and block  330  outputs a logical FALSE value at output  330   a  to block  332 . It should be noted that hysteresis may be incorporated into this comparison so that jitter or rapid state changing of the output may be avoided. 
     At block  332 , block diagram  300  applies engine stop/start or pull-down/pull-up logic to determine whether the desired engine state is on (e.g., rotating and combusting fuel) or off (e.g., not rotating and not combusting fuel). In one example, block  312  determines the desired engine state according to input from block  302 , block  306 , block  310 , block  314 , block  318 , block  322 , block  326 , and block  330 . In one example, if any of the pull-down inhibit signals is logically TRUE, the engine pull-down is inhibited. For example, if block  302  outputs an engine pull-down request that is based on vehicle speed being zero while the vehicle&#39;s brake pedal is applied and one of blocks  306  and  310  outputs a logical TRUE value, then engine pull-down is inhibited. However, if block  302  outputs an engine pull-down request that is based on vehicle speed being zero while the vehicle&#39;s brake pedal is applied and blocks  306  and  310  output logical FALSE values, then engine pull-down is not inhibited. Block  332  outputs the requested engine state at output  332   a.    
     At block  336 , block diagram  300  determines which engine starting device is to be applied to start the engine if the desired engine state is on. Block  336  judges which engine starting device is to be applied to start the engine based on inputs from block  334 . Block  334  provides vehicle operating conditions to block  336 . For example, block  334  may output engine oil temperature, ambient temperature, and engine cylinder head temperature to block  336 . Block  336  may select starter  96  of  FIG.  1    to start the engine when these three temperatures are each below 5° C. On the other hand, block  336  may select BISG  219  to start the engine when engine oil temperature and cylinder head temperature are greater than 20° C. Further, block  336  may select ISG  240  to start the engine when BISG  219  is degraded. Block  336  commands one of engine starting device  96 ,  219 , or  240  to start the engine when an engine start is requested. The engine starting device  96 ,  218 , or  240  that has been commanded to start the engine rotates the engine at a predetermined cranking speed (e.g., 240 RPM). The engine may be started via supplying spark and fuel to the engine&#39;s cylinders. Engine operating conditions are provided to the engine control system  318  via the sensors and actuators described herein. 
     Thus, the method of  FIGS.  3 A and  3 B  provides for a method for operating a vehicle, comprising: inhibiting an automatic engine pull-down via a controller based on a minimum engine running time for enabling automatic engine pull-down and based on a minimum vehicle travel distance for enabling automatic engine pull-down. The method further comprises cranking an engine via one of a plurality of engine starting devices. The method includes where inhibiting the automatic engine pull-down is further based on an amount of continuous engine run time since an engine most recently stopped being less than the minimum engine running time for enabling automatic engine pull-down. The method includes where inhibiting the automatic engine pull-down is further based on an actual total distance traveled by a vehicle since an engine began continuously running after the engine most recently stopped being less than the minimum vehicle travel distance for enabling automatic engine pull-down. The method further comprises requesting the automatic engine pull-down in response to vehicle operating conditions. The method includes where the vehicle operating conditions include vehicle speed and brake pedal position. The method includes where the automatic engine pull-down includes ceasing fuel delivery to an engine. 
     The method of  FIGS.  3 A and  3 B  also provides for a method for operating a vehicle, comprising: inhibiting an automatic engine pull-down via a controller based on a minimum engine running time for enabling automatic engine pull-down and based on a minimum vehicle travel distance for enabling automatic engine pull-down, wherein the minimum engine running time for enabling automatic engine pull-down varies as a function of a ratio of an actual total number of engine starts generated via an engine starting device and an actual total distance traveled by a vehicle since the engine starting device was installed in the vehicle. The method includes wherein the minimum vehicle travel distance for enabling automatic engine pull-down varies as a function of the ratio of the actual total number of engine starts generated via an engine starting device and the actual total distance traveled by the vehicle since the engine starting device was installed in the vehicle. The method further comprises automatically starting an engine when the automatic engine pull-down is not inhibited. The method further comprises permitting engine pull-down in response to an operator initiated engine pull-down request. The method includes wherein the actual total number of engine starts generated via the engine starting device begins with an engine start that immediately follows installation of the engine starting device into the vehicle. 
     Referring now to  FIG.  4   , an example vehicle operating sequence is shown. The sequence of  FIG.  4    may be generated via the system of  FIGS.  1  and  2    in cooperation with the method described by the block diagram of  FIG.  3   . Vertical lines at times t 0 -t 2  represent times of interest during the sequence. The plots in  FIG.  4    are time aligned and occur at the same time. 
     The first plot from the top of  FIG.  4    is a plot of the actual total distance traveled by the vehicle since a particular one of the engine starting devices (e.g., the BISG) was installed in the vehicle versus time. The vertical axis represents the total distance traveled by the vehicle since a particular one of the engine starting devices (e.g., the BISG) was installed in the vehicle and the total distance 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. Trace  402  represents total distance traveled by the vehicle since a particular one of the engine starting devices (e.g., the BISG) was installed in the vehicle. 
     The second plot from the top of  FIG.  4    is a plot of an actual total number of engine starts since the particular engine starting device (e.g., the BISG) was installed in the vehicle. The vertical axis represents the total number of engine starts since a particular one of the engine starting devices (e.g., the BISG) was installed in the vehicle and the number of engine starts since the particular one of the engine starting devices was installed in the vehicle increases in the direction of the vertical axis arrow. Trace  404  represents the total number of engine starts since a particular one of the engine starting devices (e.g., the BISG) was installed in the vehicle. The horizontal axis represents time and time increases from the left side of the plot to the right side of the plot. 
     The third plot from the top of  FIG.  4    is a plot of a cumulative actual total number of engine starts per unit distance traveled (e.g., 0.3 engine starts per kilometer) versus time. The vertical axis represents the cumulative actual total number of engine starts per unit distance traveled and cumulative actual total number of engine starts per unit distance traveled increases in the direction of the vertical axis arrow. Trace  406  represents the cumulative actual total number of engine starts per unit distance traveled by the vehicle. The horizontal axis represents time and time increases from the left side of the plot to the right side of the plot. 
     The fourth plot from the top of  FIG.  4    is a plot of an error of the cumulative actual total number of engine starts per unit distance traveled versus time. The vertical axis represents the error of the cumulative actual total number of engine starts per unit distance traveled and error of the cumulative actual total number of engine starts per unit distance traveled increases in the direction of the vertical axis arrow. Trace  408  represents the error of the cumulative actual total number of engine starts per unit distance traveled by the vehicle. The horizontal axis represents time and time increases from the left side of the plot to the right side of the plot. 
     The fifth plot from the top of  FIG.  4    is a plot of an amount of time that the engine has been continuously been running since the more recent engine stop versus time. The vertical axis represents the amount of time that the engine has been continuously been running since the more recent engine stop and the amount of time that the engine has been continuously been running since the more recent engine stop increases in the direction of the vertical axis arrow. The horizontal axis represents time and time increases from the left side of the plot to the right side of the plot. Trace  410  represents the amount of time that the engine has been continuously been running since the more recent engine stop. Horizontal line  450  represents a minimum engine run time since a most recent engine stop that has to occur before engine pull-down may be enabled. 
     The sixth plot from the top of  FIG.  4    is a plot of a distance that the vehicle has traveled while the engine has been continuously running since the more recent engine stop versus time. The vertical axis represents the distance that the vehicle has traveled while the engine has been continuously running since the more recent engine stop and the distance that the vehicle has traveled while the engine has been continuously been running since the more recent engine stop increases in the direction of the vertical axis arrow. The horizontal axis represents time and time increases from the left side of the plot to the right side of the plot. Trace  412  represents the distance that the vehicle has traveled while the engine has been continuously running since the more recent engine stop. Horizontal line  452  represents a minimum distance that the vehicle has to travel while the engine has been continuously running since the more recent engine stop for automatic engine pull-down to be enabled. 
     The seventh plot from the top of  FIG.  4    is a plot of a state that indicates automatic engine pull-down is inhibited due to insufficient engine running time versus time. The vertical axis represents the state that indicates automatic engine pull-down is inhibited due to insufficient engine running time and the state that indicates that automatic engine pull-down is inhibited due to insufficient engine running time is true when trace  414  is at a higher level near the vertical axis arrow. The state that indicates that automatic engine pull-down is inhibited due to insufficient engine running time is not true when trace  414  is at a lower level near the horizontal axis. The horizontal axis represents time and time increases from the left side of the plot to the right side of the plot. Trace  414  represents the state that indicates automatic engine pull-down is inhibited due to insufficient engine running time. 
     The eighth plot from the top of  FIG.  4    is a plot of a state that indicates automatic engine pull-down is inhibited due to insufficient engine running distance versus time. The vertical axis represents the state that indicates that automatic engine pull-down is inhibited due to insufficient engine running distance and the state that indicates that automatic engine pull-down is inhibited due to insufficient engine running distance is true when trace  416  is at a higher level near the vertical axis arrow. The state that indicates that automatic engine pull-down is inhibited due to insufficient engine running distance is not true when trace  416  is at a lower level near the horizontal axis. The horizontal axis represents time and time increases from the left side of the plot to the right side of the plot. Trace  416  represents the state that indicates that automatic engine pull-down is inhibited due to insufficient engine running distance (e.g., the vehicle and engine have not traveled a sufficient distance to permit automatic engine pull-down). 
     At time t 0 , the engine is running and the vehicle is moving (not shown). The total distance traveled by the vehicle since the engine starting device was installed in the vehicle is at middle level and it is increasing gradually. The total number of engine starts since the engine starting device was installed in the vehicle is at a constant level. The cumulative number of engine starts per unit distance traveled (e.g., 0.3 starts/kilometer) is at a lower level and the cumulative number of engine starts per distance traveled error is positive, which indicates that the engine starts per unit distance traveled are greater than a threshold number of engine starts per unit distance traveled. The amount of time since a most recent time that the engine was stopped is increasing and it is less than the minimum engine run time since a most recent engine stop that has to occur or pass to enable automatic engine pull-down. The distance that the vehicle has traveled since the engine most recently began running after a most recent engine stop (e.g., no engine rotation) is increasing and it is less than the minimum distance that the vehicle has to travel while the engine has been continuously running since the most recent engine stop before automatic engine pull-down may be enabled. Automatic engine pull-down due to insufficient engine run time is inhibited. In addition, automatic engine pull-down due to insufficient engine run distance is inhibited. 
     Between time t 0  and time t 1 , the total distance traveled by the vehicle increases and the total number of engine starts since engine starting device installation remains unchanged. The cumulative number of engine starts per unit distance traveled decreases and the cumulative engine starts per distance traveled error decreases. The amount of time since a most recent time that the engine was stopped is increasing and it is less than the minimum engine run time since a most recent engine stop that has to occur or pass to enable automatic engine pull-down. The distance that the vehicle has traveled since the engine most recently began running after a most recent engine stop (e.g., no engine rotation) is increasing and it is less than the minimum distance that the vehicle has to travel while the engine has been continuously running since the most recent engine stop before automatic engine pull-down may be enabled. Automatic engine pull-down due to insufficient engine run time is inhibited. In addition, automatic engine pull-down due to insufficient engine run distance is inhibited. 
     At time t 1 , the amount of time since a most recent time that the engine was stopped is increasing and it is greater than the minimum engine run time since a most recent engine stop that has to occur or pass to enable automatic engine pull-down. The distance that the vehicle has traveled since the engine most recently began running after a most recent engine stop (e.g., no engine rotation) is increasing and it is less than the minimum distance that the vehicle has to travel while the engine has been continuously running since the most recent engine stop before automatic engine pull-down may be enabled. Automatic engine pull-down due to insufficient engine run time is no longer inhibited. The automatic engine pull-down due to insufficient engine run distance is inhibited. 
     At time t 2 , the amount of time since a most recent time that the engine was stopped continues to increase and it is greater than the minimum engine run time since a most recent engine stop that has to occur or pass to enable automatic engine pull-down. The distance that the vehicle has traveled since the engine most recently began running after a most recent engine stop (e.g., no engine rotation) is increasing and it is greater than the minimum distance that the vehicle has to travel while the engine has been continuously running since the most recent engine stop before automatic engine pull-down may be enabled. Automatic engine pull-down due to insufficient engine run time is no longer inhibited. The automatic engine pull-down due to insufficient engine run distance is no longer inhibited. 
     In this way, inhibiting of automatic engine pull-down may be performed based on a distance traveled by a vehicle and an amount of time that an engine has been continuously running. Further, the distance traveled by the vehicle for enabling automatic engine pull-down may be adjusted as a function of an actual total number of engine starts since an engine starting device was installed in a vehicle. 
     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, 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.