Abstract:
Systems and methods for improving operation of a start/stop vehicle are presented. One method includes deactivating an engine start/stop mode in response to an electrical load of a trailer coupled to a vehicle. By deactivating the engine start/stop mode, it may be possible to conserve consumption of electrical energy and maintain state of battery charge to ensure the vehicle has sufficient electrical energy to restart the engine.

Description:
FIELD 
     The present description relates to a system and methods for controlling whether or not an engine is automatically stopped and started. The methods may be particularly useful for hybrid vehicles that include a driveline with a disconnect clutch. 
     BACKGROUND AND SUMMARY 
     An engine of a vehicle may be automatically stopped when if there is no immediate need for the engine&#39;s torque output. The engine may be restarted if a greater amount of torque is requested to propel the vehicle. Further, if the vehicle is a hybrid vehicle, it may be desirable to open a driveline disconnect clutch when engine rotation is being stopped so that a driveline integrated starter/generator may efficiently provide torque to propel the vehicle. The driveline disconnect clutch may be closed and the engine may be restarted when a driver demand torque increases. However, frequently starting and stopping the vehicle may increase electrical energy consumption of the vehicle. Further, if the engine has to restart to provide low levels of vehicle acceleration, stopping the engine may not conserve as much fuel as is desired and vehicle driveline degradation may increase. 
     The inventors herein have recognized the above-mentioned disadvantages and have developed a method for operating an engine of a vehicle, comprising: in an engine start/stop mode, selectively automatically stopping and starting the engine in response to vehicle operating conditions while a transmission of the vehicle is in a forward gear; and deactivating the engine start/stop mode in response to an electrical load of a trailer coupled to the vehicle. 
     By deactivating an engine start/stop mode in response to an electrical load of a trailer coupled to a vehicle, it may be possible to provide the technical result of reducing electrical consumption and maintaining battery state of charge so that the vehicle may be reliably restarted. Additionally, the engine start/stop mode may be deactivated in response to vehicle mass and/or the combined mass of the vehicle and a trailer. Consequently, the vehicle may respond more rapidly and with more torque than compared to if the vehicle were operated in an engine start/stop mode. Thus, vehicle launch may be improved by deactivating the engine start/stop mode. 
     The present description may provide several advantages. In particular, the approach may reduce electrical energy consumption by a vehicle so that there may be sufficient electrical energy to restart an engine of the vehicle. Further, the approach may improve launch of a vehicle from stop when a trailer is coupled to the vehicle. Further still, the approach may reduce driveline wear, thereby increasing the operating life of the driveline. 
     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 shows an example vehicle driveline configuration; 
         FIG. 3  shows an example vehicle and trailer configuration; 
         FIG. 4  shows an example electrical circuit providing electrical power to a trailer; 
         FIG. 5A  shows a first example electrical circuit for detecting presence of a trailer; 
         FIG. 5B  shows a second example electrical circuit for detecting presence of a trailer; 
         FIG. 6  shows a prophetic vehicle operating sequence; and 
         FIG. 7  is a flowchart showing one example method for operating an engine. 
     
    
    
     DETAILED DESCRIPTION 
     The present description is related to controlling operation of an engine of a start/stop vehicle. In one example, the engine may be included in a hybrid vehicle as is shown in  FIG. 2 . The engine may be part of a vehicle as shown in  FIG. 3 . The vehicle may also tow a trailer as shown in  FIG. 3 . The trailer and vehicle may be electrically coupled as shown in  FIG. 4  so that the trailer has running lights and brake lights. The presence or absence of a trailer coupled to the vehicle may be determined via the circuits shown in  FIGS. 5A and 5B . The engine start/stop functionality may be provided as shown in  FIG. 6  according to the method of  FIG. 7 . The method of  FIG. 7  describes various vehicle operating conditions that may contribute to activating or deactivating an automatic engine start/stop mode. 
     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  includes combustion chamber  30  and cylinder walls  32  with piston  36  positioned therein and connected to crankshaft  40 . Flywheel  97  and ring gear  99  are coupled to crankshaft  40 . Starter  96  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 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 cam  51  and exhaust cam  53  may be moved relative to crankshaft  40 . 
     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. Alternatively, fuel may be injected to an intake port, which is known to those skilled in the art as port injection. Fuel injector  66  delivers liquid fuel in proportion to the pulse width of signal 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 addition, intake manifold  44  is shown communicating with optional electronic throttle  62  which adjusts a position of throttle plate  64  to control air flow from air intake  42  to intake manifold  44 . In one example, a low pressure direct injection system may be used, where fuel pressure can be raised to approximately 20-30 bar. Alternatively, a high pressure, dual stage, fuel system may be used to generate higher fuel pressures. In some examples, 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. 
     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 . 
     Catalytic converter  70  can include multiple catalyst bricks, in one example. In another example, multiple emission control devices, each with multiple bricks, can be used. Catalytic converter  70  can be a three-way type catalyst in one example. A temperature of catalytic converter  70  may be measured or estimated via engine speed, engine load, engine coolant temperature, and spark timing. 
     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  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 ; a measure of road grade from inclinometer  35 , and a measurement of throttle position from sensor  58 . 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. 
     In some examples, the engine may be coupled to an electric motor/battery system in a hybrid vehicle as shown in  FIG. 2 . Further, in some examples, other engine configurations may be employed, for example a diesel engine. 
     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 driveline  200  and vehicle  290 . Driveline  200  may be powered by engine  10 . Engine  10  may be started with an engine starting system shown in  FIG. 1  or via driveline integrated starter/generator (DISG)  240 . Further, engine  10  may generate or adjust torque via torque actuator  204 , such as a fuel injector, throttle, etc. 
     An engine output torque may be transmitted to an input side of dual mass flywheel  232 . Engine speed as well as dual mass flywheel input side position and speed may be determined via engine position sensor  118 . Dual mass flywheel  232  may include springs and separate masses (not shown) for dampening driveline torque disturbances. The output side of dual mass flywheel  232  is shown being mechanically coupled to the input side of driveline disconnect clutch  236 . Disconnect clutch  236  may be electrically or hydraulically actuated. A position sensor  234  is positioned on the disconnect clutch side of dual mass flywheel  232  to sense the output position and speed of the dual mass flywheel  232 . The downstream side of disconnect clutch  236  is shown mechanically coupled to DISG input shaft  237 . 
     DISG  240  may be operated to provide torque to driveline  200  or to convert driveline torque into electrical energy to be stored in electric energy storage device  275 . DISG  240  has a higher output torque capacity than starter  96  shown in  FIG. 1  and may be used to start engine  10 . Further, DISG  240  directly drives driveline  200  or is directly driven by driveline  200 . There are no belts, gears, or chains to couple DISG  240  to driveline  200 . Rather, DISG  240  rotates at the same rate as driveline  200 . Electrical energy storage device  275  may be a battery, capacitor, or inductor. The downstream side of DISG  240  is mechanically coupled to the impeller  285  of torque converter  206  via shaft  241 . The upstream side of the DISG  240  is mechanically coupled to the disconnect clutch  236 . Torque converter  206  includes a turbine  286  to output torque 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). Torque 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. Torque converter turbine speed and position may be determined via position sensor  239 . In some examples,  238  and/or  239  may be torque sensors or may be combination position and torque sensors. 
     When torque converter lock-up clutch  212  is fully disengaged, torque converter  206  transmits engine torque 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 torque is directly transferred via the torque converter clutch to an input shaft (not shown) of transmission  208 . Alternatively, the torque converter lock-up clutch  212  may be partially engaged, thereby enabling the amount of torque directly relayed to the transmission to be adjusted. The controller  12  may be configured to adjust the amount of torque 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. 
     Automatic transmission  208  includes gear clutches (e.g., gears 1-6)  211  and forward clutch  210 . The gear clutches  211  and the forward clutch  210  may be selectively engaged to propel a vehicle. Torque output from the automatic transmission  208  may in turn be relayed to wheels  216  to propel the vehicle via output shaft  260 . Specifically, automatic transmission  208  may transfer an input driving torque at the input shaft  270  responsive to a vehicle traveling condition before transmitting an output driving torque to the wheels  216 . 
     Further, a frictional force may be applied to wheels  216  by engaging wheel brakes  218 . In one example, wheel brakes  218  may be engaged in response to the driver pressing his foot on a brake pedal (not shown). In other examples, controller  12  or a controller linked to controller  12  may apply engage wheel brakes. In the same way, a frictional force may be reduced to wheels  216  by disengaging wheel brakes  218  in response to the driver releasing his foot from a brake pedal. Further, vehicle brakes may apply a frictional force to wheels  216  via controller  12  as part of an automated engine stopping procedure. 
     A mechanical oil pump  214  may be in fluid communication with automatic transmission  208  to provide hydraulic pressure to engage various clutches, such as forward clutch  210 , gear clutches  211 , and/or torque converter lock-up clutch  212 . Mechanical oil pump  214  may be operated in accordance with torque converter  206 , and may be driven by the rotation of the engine or DISG via input shaft  241 , for example. Thus, the hydraulic pressure generated in mechanical oil pump  214  may increase as an engine speed and/or DISG speed increases, and may decrease as an engine speed and/or DISG speed decreases. 
     Controller  12  may be configured to receive inputs from engine  10 , as shown in more detail in  FIG. 1 , and accordingly control a torque output of the engine and/or operation of the torque converter, transmission, DISG, clutches, and/or brakes. As one example, an engine torque 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 torque output by controlling a combination of fuel pulse width, fuel pulse timing, and air charge. In all cases, engine control may be performed on a cylinder-by-cylinder basis to control the engine torque output. Controller  12  may also control torque output and electrical energy production from DISG by adjusting current flowing to and from windings of DISG as is known in the art. 
     When idle-stop conditions are satisfied, controller  12  may initiate engine shutdown by shutting off fuel and spark to the engine. However, the engine may continue to rotate in some examples. Further, to maintain an amount of torsion in the transmission, the controller  12  may ground rotating elements of transmission  208  to a case  259  of the transmission and thereby to the frame of the vehicle. In particular, the controller  12  may engage one or more transmission clutches, such as forward clutch  210 , and lock the engaged transmission clutch(es) to the transmission case  259  and vehicle. A transmission clutch pressure may be varied (e.g., increased) to adjust the engagement state of a transmission clutch, and provide a desired amount of transmission torsion. When restart conditions are satisfied, and/or a vehicle operator wants to launch the vehicle, controller  12  may reactivate the engine by resuming cylinder combustion. 
     A wheel brake pressure may also be adjusted during the engine shutdown, based on the transmission clutch pressure, to assist in tying up the transmission while reducing a torque transferred through the wheels. Specifically, by applying the wheel brakes  218  while locking one or more engaged transmission clutches, opposing forces may be applied on transmission, and consequently on the driveline, thereby maintaining the transmission gears in active engagement, and torsional potential energy in the transmission gear-train, without moving the wheels. In one example, the wheel brake pressure may be adjusted to coordinate the application of the wheel brakes with the locking of the engaged transmission clutch during the engine shutdown. As such, by adjusting the wheel brake pressure and the clutch pressure, the amount of torsion retained in the transmission when the engine is shutdown may be adjusted. In alternative examples, the vehicle system may be a series or parallel hybrid, a plug in hybrid, a motor only vehicle, or other known type of driveline. 
     Referring now to  FIG. 3 , an example vehicle and trailer configuration is shown. Vehicle  290  is shown mechanically coupled to trailer  350 . Additionally, vehicle  290  may be electrically coupled to trailer  350  as shown in  FIG. 4  or by another known means. Trailer includes brakes  320  which may be electrically actuated in response to an electrical signal from controller  12  or a similar controller in vehicle  290 . Trailer  350  also includes running lights  325  to show the position of trailer  350 . Trailer  350  also includes brake lights  328  to indicate when a driver of vehicle  290  is applying vehicle brakes. Trailer  350  includes a tongue  310  that is coupled to receiver  302 . Strain gauge sensor  304  may provide an indication of when trailer  350  is coupled to vehicle  290 . In other examples, trailer  350  may be of a goose neck configuration or other configuration. Further, controller  12  may communicate with trailer  350  via a CAN bus, smart bus, wireless, network, or other may for communicating between controllers. 
     Referring now to  FIG. 4 , an example circuit providing electrical power to a trailer is shown. Trailer  350  includes an electrical connector  420  with electrical contacts leading to electrical brakes  402 , running lights  406 , and brake lights  404 . Vehicle  290  includes circuits  410  for detecting the presence of trailer  350  and monitoring current used by trailer  350 . In one example, circuit  410  is comprised of a smart field effect transistor that monitors current flow to trailer  350 . Thus, current to electrical brakes  402 , running lights  406 , and brake lights  404  may be determined. In another example, circuit  410  may be similar to the circuit shown in  FIG. 5A . 
     Circuits  410  may be active when trailer  350  is coupled to vehicle  290  so that current flows from circuits  410  to the trailer components. The amount of current flow is measured or routed to controller  12  for determining whether or not the engine start/stop mode is to be activated. Additionally, the current flow may be used to determine whether or not a driveline disconnect clutch should be opened. 
     Referring now to  FIG. 5A , a first example circuit for determining whether or not a trailer is coupled to a vehicle is shown. Additionally, circuit  410  may supply power to the trailer&#39;s electrical components. 
     Circuit  410  includes a first resistor  506  between power source VPWR and diode  507 . Circuit  410  also includes a second resistor  504  and a capacitor  509 . When brake light  404  is connected to circuit  410 , a voltage at node  511  changes. The voltage at node  511  may be monitored by controller  12  to determine whether or not a trailer is coupled to the vehicle. 
     Referring now to  FIG. 5B , a second example electrical circuit for detecting the presence or absence of a trailer coupled to the vehicle is shown. The second circuit comprises a strain gauge  554  or alternatively a pressure sensor. If the vehicle is accelerating or decelerating and the trailer is connected to the vehicle, the strain gauge  554  outputs a voltage or current representative of the force applied to receiver  302 . Strain gauge  554  is shown coupled to receiver pin  556  and output of strain gauge  554  reflects force applied to trailer ball  550  by trailer  350  shown in  FIG. 3 . Thus, by monitoring the output of strain gauge  554  during driving conditions, it may be determined whether or not a trailer  350  is mechanically coupled to vehicle  290 . 
     Thus, the system of  FIGS. 1-5  provides for a vehicle system, comprising: a vehicle an engine coupled to the vehicle and a transmission; a trailer coupled to the vehicle; and a controller including non-transitory instructions executable to deactivate an engine start/stop mode in response to a condition of the trailer. The vehicle system includes where the condition of the trailer include the electrical load of the trailer. The vehicle system includes where the engine start stop/mode is deactivated in response to a current drawn from the vehicle to the trailer exceeding a threshold current. The vehicle system includes where the condition of the trailer is a mass of the trailer. The vehicle system further comprises a driveline disconnect clutch and deactivating opening the driveline disconnect clutch in response to the condition of the trailer. The vehicle system further comprises additional instructions to deactivated the engine start/stop mode in response to a road grade. 
     Referring now to  FIG. 6 , an example driveline operating sequence is shown. The sequence of  FIG. 6  may be provided via the system of  FIGS. 1 and 2  executing instructions stored in non-transitory memory according to the method of  FIG. 7 . The sequence of  FIG. 6  shows vertical markers T0-T9 which indicate particular times of interest during the operating sequence. All plots in  FIG. 6  are referenced to the same time scale and occur at the same time. 
     The first plot from the top of  FIG. 6  is a plot of engine operating state versus time. The X axis represents time and time begins at the left side of  FIG. 6  and increases to the right side of  FIG. 6 . The Y axis represents engine operating state and the engine is operating when the engine operating state is at a high level. The engine is not operating when the engine operating state is at a lower level. 
     The second plot from the top of  FIG. 6  is a plot of driver demand torque versus time. The X axis represents time and time begins at the left side of  FIG. 6  and increases to the right side of  FIG. 6 . The Y axis represents driver demand torque and driver demand torque increases in the direction of the Y axis arrow. Horizontal line  602  represents a threshold driver demand torque where the engine may be started to provide the requested driver demand torque. 
     The third plot from the top of  FIG. 6  is a plot of driveline disconnect clutch state versus time. The X axis represents time and time begins at the left side of  FIG. 6  and increases to the right side of  FIG. 6 . The Y axis represents driveline disconnect clutch state and the driveline disconnect clutch state is open when the trace is at a lower level and closed when the trace is at a higher level. 
     The fourth plot from the top of  FIG. 6  is a plot of engine start/stop enable status versus time. The X axis represents time and time begins at the left side of  FIG. 6  and increases to the right side of  FIG. 6 . The Y axis represents engine start/stop enable status and engine start/stop mode is enabled when the trace is at a higher level. Engine start/stop mode is not enabled when the trace is at a lower level. 
     The fifth plot from the top of  FIG. 6  is a plot of vehicle mass versus time. The X axis represents time and time begins at the left side of  FIG. 6  and increases to the right side of  FIG. 6 . The Y axis represents vehicle mass and vehicle mass increases in the direction of the Y axis arrow. Horizontal line  604  represents a threshold vehicle mass where engine start/stop mode may be deactivated so as to provide improved vehicle launch in the presence of greater vehicle mass. 
     The sixth from the top of  FIG. 6  is a plot of trailer mass versus time. The X axis represents time and time begins at the left side of  FIG. 6  and increases to the right side of  FIG. 6 . The Y axis represents trailer mass and trailer mass increases in the direction of the Y axis arrow. 
     The seventh from the top of  FIG. 6  is a plot of road grade versus time. The X axis represents time and time begins at the left side of  FIG. 6  and increases to the right side of  FIG. 6 . The Y axis represents road grade and road grade increases in the direction of the Y axis arrow. 
     The eighth from the top of  FIG. 6  is a plot of trailer electrical current consumption versus time. The X axis represents time and time begins at the left side of  FIG. 6  and increases to the right side of  FIG. 6 . The Y axis represents trailer electrical current consumption and trailer electrical current consumption increases in the direction of the Y axis arrow. Horizontal line  606  represents a threshold trailer current consumption level where engine start/stop mode may be deactivated so as to improve the possibility of engine starting and elevate battery state of charge. 
     At time T0, the engine operating state is at a higher level indicating that the engine is operating. The driver demand torque is also at a higher level. The driver demand torque may be determined from a position of an accelerator pedal. The driveline disconnect clutch is in a closed state and the engine start/stop enable status is indicating that engine start/stop mode is deactivated. The engine stop/start mode is deactivated in response to the road grade being at a higher level. The trailer mass is zero indicating that a trailer is not coupled to the vehicle. The trailer current consumption is also at zero. 
     At time T1, the road grade has been reduced to a level where engine start/stop may be activated. Therefore, the engine start/stop enable status changes state to a higher level to indicate that the engine may be operated in a start/stop mode. The engine remains operating and the driver demand torque remains at a higher but reduce level as compared to at time T0. The driveline disconnect clutch also remains in a closed state and the vehicle mass remains constant. The trailer mass remains at zero to indicate that no trailer is coupled to the vehicle. The trailer current consumption also remains at a lower level. 
     At time T2, the driver demand torque is reduced to a low level while engine start/stop mode is active. Shortly thereafter, the driveline disconnect clutch opens as indicated and the engine operating state transitions to a lower level. The engine stops rotating in response to the engine operating state changing to the lower level. The vehicle mass is at the same level at time T2 as at time T0, but mass is added to the vehicle shortly thereafter increasing the vehicle payload. The road grade continues to be reduced and trailer current consumption is zero. 
     Between time T2 and time T3, the vehicle mass is increased and the driver demand torque increases in response to a driver applying an accelerator pedal (not shown). The engine remains stopped and the driveline disconnect remains open. 
     At time T3, the driver demand torque increases to a level where the engine is restarted in response to the driver demand torque so that the driver demand torque may be met by the driveline. In this example, the engine is started via a starter while the driveline disconnect clutch is open. However, the engine may be started via the driveline disconnect clutch if desired. The driveline disconnect clutch closes shortly thereafter in response to the driver demand torque so that engine torque may be provided to the driveline. Engine start/stop mode remains enabled and vehicle mass does not increase. Further, trailer mass remains at zero as does trailer current consumption. The road grade continues to be reduced. 
     At time T4, the drive demand torque is again reduced to a level where the engine operating state transitions to a lower level and engine rotation stops. The driveline disconnect clutch is also opened in response to the decrease in driver demand torque. The engine start/stop remains enabled while the vehicle mass, trailer mass, and trailer current consumption remain unchanged. The road grade is also reduced to zero. 
     Between time T4 and time T5, the vehicle mass is increased further to a vehicle mass that is greater than the threshold vehicle mass where engine start/stop mode may be deactivated. In this example, the vehicle mass is determined when the vehicle is accelerating or decelerating. Therefore, the engine start/stop mode is not deactivated until the vehicle begins to accelerate. However, where suspension sensors are available, the engine start/stop mode may be deactivated as soon as the vehicle mass is greater than the threshold vehicle mass and the engine may be automatically restarted in response to the increase in vehicle mass. 
     At time T5, the driver demand torque increases in response to a driver depressing an accelerator pedal and the engine start/stop mode is deactivated in response to the vehicle mass increasing to greater than threshold mass  604 . The engine is restarted in response to deactivating the engine start/stop mode and the driveline disconnect clutch is closed shortly thereafter in response to the engine start/stop mode being deactivated. The trailer mass and electrical consumption remains unchanged and the road grade remains at zero. 
     At time T6, the driver demand torque is reduced again in response to a driver releasing an accelerator pedal. The engine continues to operate since the engine operating state is at a higher level. The driveline disconnect clutch remains engaged in response to the engine start/stop mode being deactivated as indicated by the engine start/stop enable status being at a lower level. The vehicle mass remains at a higher level and a trailer is not coupled to the vehicle. The road grade remains zero and trailer current consumption remains at zero. 
     Between time T6 and time T7, the vehicle mass is lowered in response to a driver removing a portion of the vehicle payload. Additionally, the driver couples a trailer to the vehicle as indicated by the increase in trailer mass. The trailer electrical current consumption also increases. 
     At time T7, the driver demand torque increases in response to a driver applying an accelerator pedal. The engine start/stop mode is also reactivated in response to the reduction in vehicle mass and since the combined trailer mass and vehicle mass is less than a threshold mass. The engine remains active and the driveline disconnect clutch remains closed in response to the increasing driver demand torque. 
     At time T8, the driver demand torque decreases in response to a driver releasing an accelerator pedal. The driveline disconnect clutch opens and the engine operating state transitions to a lower level to indicate that the engine stops rotating in response to the reduced driver demand torque. The engine start/stop mode remains active and the vehicle mass remains at a lower level. 
     Between time T8 and time T9, the driver increases the trailer mass via increasing the trailer payload. The vehicle mass remains at a same level since time T8. The road grade remains at zero. The driver demand torque also begins to increase in response to a driver applying an accelerator pedal. 
     At time T9, the engine start/stop status changes state to deactivate the engine start/stop mode in response to the combination of vehicle mass and trailer mass exceeds a threshold mass. The engine is restarted in response to the change in the engine start/stop status even though the driver demand torque is at a lower level. The driveline disconnect clutch closes in response to the engine start/stop status deactivating the engine start/stop mode. The vehicle mass remains unchanged and the road grade remains zero. 
     After time T9, the engine start/stop mode remains deactivated since the combined vehicle mass and trailer mass is greater than a threshold mass. Further, the trailer current consumption exceeds the current consumption threshold  606 . Therefore, the engine start/stop mode would be deactivated even if the combined trailer mass and vehicle mass were less than a threshold. 
     In this way, the engine start/stop mode may be selectively activated and deactivated in response to vehicle operating conditions. Further, the driveline disconnect clutch may be activated and deactivated in a similar fashion. 
     Referring now to  FIG. 7 , a method for operating an engine and driveline of a vehicle is shown. The method of  FIG. 7  may be stored as executable instructions in non-transitory memory of a controller such as controller  12  in  FIG. 1 . Thus, the method of  FIG. 7  may be incorporated in to a system as shown in  FIGS. 1 and 2 . The method of  FIG. 7  may also provide the sequence shown in  FIG. 6 . In some examples, the method of  FIG. 7  may be called in response to coupling an electrical connector of a trailer to the vehicle so that engine start/stop mode may be reassessed. 
     At  702 , method  700  judges whether or not circuits or other hardware for detecting whether or not a trailer is coupled to the vehicle are present. In one example, a variable in controller memory may be set or not set based on whether or not hardware for detecting a trailer is present. If method  700  judges that the circuits or other hardware for detecting whether or not a trailer is coupled to the vehicle are present the answer is yes and method  700  proceeds to  704 . Otherwise, the answer is no and method  700  proceeds to  720 . 
     At  704 , method  700  judges whether or not a trailer is present based on electrical circuit input to the controller. A trailer may be detected via the circuitry shown in  FIGS. 5A and 5B , or alternatively, via a camera or a different known circuit that indicates the presence or absence of a trailer coupled to the vehicle. For example, method  700  may judge that a trailer is mechanically and electrically coupled to a vehicle if a voltage at node  511  is greater or less than a threshold voltage. If method  700  judges that a trailer is present based on the electrical circuit, the answer is yes and method  700  proceeds to  706 . Otherwise, the answer is no and method  700  proceeds to  720 . 
     At  706 , method  700  determines vehicle electrical lighting and braking currents. In one example, vehicle lighting and braking currents may be determined via a field effect transistor that measures current flow as described in  FIG. 4 . Alternatively, vehicle lighting and braking currents may be determined via measuring a voltage across a resistor that directs electrical power to the trailer. The current to operate the vehicle&#39;s running lights may be determined separate from or with current to operate trailer brakes. Further, the trailer electrical currents may be determined at a specified frequency, or the trailer currents may be determined at specific conditions such as when the vehicle is braking Method  700  proceeds to  708  after trailer lighting and braking currents are determined. 
     Additionally, in some examples, the current drawn by the trailer may be determined during specific conditions, while brakes are being applied for example. In this way, a more representative peak current draw may be obtained. 
     At  708 , method  700  judges whether or not the currents captured at  706  are greater than a threshold current. In one example, all current supplied to the trailer is added together. If the trailer current is greater than a threshold current, the answer is yes and method  700  proceeds to  740 . Otherwise, the answer is no and method  700  proceeds to  710 . Thus, if the current drawn by the electrical load of the trailer is greater than a threshold current draw, the engine start/stop mode may be deactivated. In other words, the electrical load of the trailer is greater than desired for engine start/stop mode to be active. 
     At  740 , method  700  deactivates engine automatic start/stop mode where the engine may be stopped and started without a driver&#39;s input to a device or input that has a sole purpose of starting/stopping an engine (e.g., an on/off key switch or pushbutton). In one example, method may deactivate automatic engine start/stop mode via setting a value of a variable in memory that activates and deactivates engine start/stop mode. When engine start/stop mode is deactivated, the engine may not be automatically stopped. However, the engine may be automatically started when the engine start/stop mode is deactivated while the engine is stopped. Method  700  proceeds to exit after the engine start/stop mode is deactivated. 
     Additionally, a driveline disconnect clutch may be held in or returned to a closed state at  740 . Closing the driveline disconnect clutch may be part of a process for deactivating the engine start/stop mode. Further, in some examples, the engine stop/start mode may be held in a deactivated state once deactivated until the trailer is decoupled from the vehicle. 
     At  710 , method  700  estimates the vehicle mass. In one example vehicle mass is determined vehicle mass based on the following equations: 
     Where vehicle acceleration is zero,
 
Engine/driveline torque≈road load+grade based torque
 
Using:  T _ wh 1= R _ rr·M _ v·g ·sin(θ 1 )+ T _ rl 1
 
     Where: 
     T_wh1=Wheel Torque on grade angle=θ 1    
     T_wh2=Wheel Torque on grade angle=θ 2    
     R_rr=Driven wheel rolling radius 
     M_v=vehicle mass estimate 
     g=gravity constant 
     θ 1 =grade angle 
     T_rl1=Road load torque at the driven wheel on grade 1 
     T_rl2=Road load torque at the driven wheel on grade 2 
     Then the vehicle mass estimate is:
 
 M _ v =[( T _ wh 1 −T _ wh 2)+( T _ rl 2 −T _ rl 1)]/[ R _ rr*g *(θ 1 −θ 2 )]
 
In this example, the vehicle mass includes mass of a vehicle and of the trailer being towed by the vehicle since it has been established that the vehicle is towing a trailer at  704 . Further, the vehicle mass may include mass of passengers in the vehicle and vehicle cargo. Method  700  proceeds to  712  after vehicle mass is determined.
 
     Alternatively, if a strain gauge sensor is included as shown in  FIG. 5B , the trailer mass may be estimated based on output of the strain gauge and F=ma, where F is force, m is trailer mass, and a is acceleration. 
     At  712 , method  700  judges whether or not the combined trailer and vehicle mass is greater than a first threshold mass. The first threshold mass may be empirically determined and stored in memory. If method  700  judges that the combined vehicle and trailer mass is greater than the first threshold mass, the answer is yes and method  700  proceeds to  740 . Otherwise, the answer is no and method  700  proceeds to  714 . 
     Thus, engine start/stop mode may be activated or deactivated in response to combined mass of a vehicle and a trailer so that vehicle launch may be improved. For example, if engine start/stop mode is not activated for a large mass vehicle and trailer, it may be difficult to provide adequate vehicle acceleration after the engine has been stopped. By deactivating the engine start/stop mode, launch of a vehicle may be improved. 
     At  714 , method  400  estimates road grade. In one example, vehicle road grade may be estimated via an inclinometer. On the other hand, if vehicle mass is known, the equation at  710  may be solved for road grade. Method  700  proceeds to  716  after road grade is estimated. 
     At  716 , method  700  judges whether or not the road grade is greater than a first threshold road grade. The first threshold road grade may be empirically determined and stored in memory. If method  700  judges that the road grade is greater than the first threshold road grade, the answer is yes and method  700  proceeds to  740 . Otherwise, the answer is no and method  700  proceeds to  718 . 
     Thus, engine start/stop mode may be activated or deactivated in response to road grade so that vehicle launch may be improved. For example, if engine start/stop mode is not activated for a large road grade (e.g., a steep road), it may be difficult to provide adequate vehicle acceleration after the engine has been stopped. By deactivating the engine start/stop mode, launch of a vehicle on the road grade may be improved. 
     At  718 , method  700  enables engine automatic start/stop mode while a transmission of the vehicle is in a forward gear. The engine start/stop mode may be activated by setting a state of a variable in memory of a controller. When engine automatic start/stop mode is active, the engine may be stopped and started without a driver operating a device that has a sole purpose of starting/stopping the engine. For example, the engine may be automatically stopped in response to a brake pedal being depressed, vehicle speed less than a threshold speed, and driver demand torque being less than a threshold driver demand torque. Method  700  proceeds to exit after engine automatic start/stop has been activated. 
     Additionally, a driveline disconnect clutch may be reactivated and allowed to open and close at  718 . Opening the driveline disconnect clutch may be part of a process for activating the engine start/stop mode. 
     At  720 , method  700  judges whether or not vehicle suspension sensor are present. Vehicle suspension sensors may be determined to be present based on a value of a variable stored in controller memory. If method  700  judges that vehicle suspension sensors are present, the answer is yes and method  700  proceeds to  722 . Otherwise, the answer is no and method  700  proceeds to  724 . 
     At  722 , method  700  estimates vehicle mass based on output from vehicle suspension sensors. In one example, vehicle mass may be estimated in response to compression of the vehicle&#39;s suspension which is determined via output of vehicle suspension sensors. For example, a base vehicle suspension height may be stored in controller memory and a function or table may include mass values that correspond to a level of vehicle suspension compression. Vehicle suspension compression is determined via subtracting the vehicle suspension sensor output in compression from the vehicle suspension sensor output during base or uncompressed conditions. The amount of vehicle suspension compression is used to index the table or function of empirically determined mass values to determine the vehicle mass. In this way the vehicle payload may be determined. Additionally, the total vehicle mass including a trailer if one is coupled to the vehicle may be determined as is described at  710 . The vehicle mass determined from the vehicle suspension sensors may then be subtracted from the total vehicle mass to yield the trailer mass. Method  400  proceeds to  726  after vehicle and trailer mass are determined. 
     At  724 , method  700  estimates vehicle mass. Vehicle mass, including a trailer if one is coupled to the vehicle, may be determined as described at  710 . Method  700  proceeds to  726  after the vehicle mass is determined. 
     At  726 , method  700  judges whether or not vehicle mass is greater than a second threshold mass. The second threshold mass may be some portion including all of a gross vehicle mass. For example, the second threshold mass may be 75% of gross vehicle mass. And, the second threshold mass is less than the first threshold mass at  712 . Further, if it is established that a trailer is coupled to the vehicle, method  700  judges whether or not the gross combined mass (e.g., vehicle mass plus trailer mass) is greater than a third threshold vehicle mass. The third threshold vehicle mass may be equal or greater than the first vehicle mass at  712 . If method judges that the vehicle mass is greater than the second threshold mass or if the combined vehicle mass is greater than a third mass, the answer is yes and method  700  proceeds to  740 . Otherwise, the answer is no and method  700  proceeds to  728 . 
     At  728 , method  700  estimates the road grade as described at  714 . Method  700  proceeds to  730  after road grade is determined. 
     At  730 , method  700  judges whether or not the road grade is greater than a second threshold road grade. If method  700  judges that the road grade is greater than the second threshold road grade, the answer is yes and method  700  proceeds to  740 . Otherwise, the answer is no and method  700  proceeds to  718 . In one example, the second road grade is less than the road grade first threshold at  716  if a trailer is not coupled to the vehicle. 
     Thus, the method of  FIG. 7  provides for operating an engine of a vehicle, comprising: in an engine start/stop mode, selectively automatically stopping and starting the engine in response to vehicle operating conditions while a transmission of the vehicle is in a forward gear; and deactivating the engine start/stop mode in response to an electrical load of a trailer coupled to the vehicle. The method includes where the electrical load is based on an electrical current flow to the trailer. The method includes where the electrical load is determined when trailer brakes are applied. 
     In some examples, the electrical load includes trailer running lights and brake lights. The method further comprises deactivating opening of a driveline disconnect clutch in response to the electrical load. The method includes where the electrical load of the trailer is determined in response to coupling an electrical connector of the trailer to the vehicle. The method further comprises deactivating the engine stop/start mode in response to an estimate of vehicle mass based on vehicle suspension sensors. 
     Thus, the method of  FIG. 7  provides for operating an engine of a vehicle, comprising: in an engine start/stop mode, selectively automatically stopping and starting the engine in response to vehicle operating conditions while a transmission of the vehicle is in a forward gear; and deactivating the engine start/stop mode in response to a combined mass of the vehicle and a trailer. The method includes where the trailer mass is based on a strain sensor. The method further comprises deactivating the engine start/stop mode in response to road grade and the combined mass of the vehicle. 
     In some examples, the method further comprises deactivating the engine start/stop mode in response to an electrical load of the trailer. The method includes where deactivating the engine start/stop mode includes starting the engine and closing a driveline disconnect clutch. The method further comprises reactivating the engine start/stop mode in response to a reduction in the combined mass of the vehicle and the trailer. The method includes where the engine start/stop mode is held deactivated until the trailer is decoupled from the vehicle. 
     As will be appreciated by one of ordinary skill in the art, method described in  FIG. 7  may represent one or more of any number of processing strategies such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. As such, various steps or functions illustrated may be performed in the sequence illustrated, in parallel, or in some cases omitted. Likewise, the order of processing is not necessarily required to achieve the objects, features, and advantages described herein, but is provided for ease of illustration and description. Although not explicitly illustrated, one of ordinary skill in the art will recognize that one or more of the illustrated steps or functions may be repeatedly performed depending on the particular strategy being used. 
     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.