Abstract:
Systems and methods for improving launching of a stopped hybrid vehicle are presented. The systems and methods adjust speed of a motor to reduce lag between an increase in driver demand torque and torque being produced at vehicle wheels. In one example, motor torque is adjusted to a maximum motor torque to improve vehicle launch during select conditions where driver demand torque is not a maximum level.

Description:
FIELD 
       [0001]    The present description relates to methods and a system for launching a hybrid vehicle from rest after an engine and electric machine in the hybrid vehicle have stopped rotating. The methods may be particularly useful for hybrid vehicles that include a torque converter and an automatic transmission. 
       BACKGROUND AND SUMMARY 
       [0002]    Hybrid vehicles may include a motor and an engine to provide improved fuel economy as compared to a non-hybrid vehicle. The motor may assist the engine or operate separately from the engine to propel the vehicle. The vehicle&#39;s hydrocarbon fuel economy may be increased by stopping engine rotation and propelling the vehicle solely via the motor. Additionally, during some conditions, such as when the hybrid vehicle is stopped, it may be desirable to stop motor rotation to conserve electrical energy. Thus, there may be selected conditions when both the engine and the motor are stopped to conserve energy. However, stopping the motor and engine also stops torque converter impeller rotation which may increase a lag time between an increase in driver demand torque and producing noticeable torque at vehicle wheels. Therefore, it would be desirable to provide reduced lag in response to an increase in driver demand torque while still allowing the motor to stop for energy conservation purposes. 
         [0003]    The inventors herein have recognized the above-mentioned disadvantages and have developed a driveline method, comprising: applying a torque via a driveline integrated starter/generator (DISG) to a torque converter impeller from a condition where DISG rotation is stopped in response to a driver demand torque greater that a first threshold and less than a second threshold, the torque at least thirty percent greater than the driver demand torque. 
         [0004]    By supplying a torque that is greater than a driver demand based torque to a torque converter impeller, it may be possible to provide the technical result of reducing delay between an increase in driver demand torque and an increase in wheel torque. Further, electric machine or motor speed may be adjusted based on a compensation torque after the electric machine achieves a torque converter fluid force transfer speed so that wheel torque increases smoothly at a time when transmission pump output pressure is increasing. In this way, the torque converter impeller speed may be accelerated quickly to a speed where a transmission pump output pressure increases and torque transfer to the torque converter turbine begins. After reaching the torque converter fluid force transfer speed, the torque converter impeller speed may be adjusted to provide torque at the torque converter turbine that is related to the driver demand torque. As a result, accelerator tip-in (e.g., increasing accelerator pedal position) response may be improved by reducing torque delay so that the driver demand torque may be applied to vehicle wheels sooner. 
         [0005]    The present description may provide several advantages. In particular, the approach may reduce wheel torque production delay in a driveline. Further, the approach may allow driver demand torque to be followed more closely. Further still, the approach may allow a vehicle to perform better after the vehicle&#39;s motor has stopped rotating to conserve electrical energy. 
         [0006]    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. 
         [0007]    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 
         [0008]    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: 
           [0009]      FIG. 1  is a schematic diagram of an engine; 
           [0010]      FIG. 2  shows an example vehicle driveline configuration; 
           [0011]      FIGS. 3 and 4  show example vehicle launch sequences; and 
           [0012]      FIG. 5  shows an example method for improving launch of a hybrid vehicle. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    The present description is related to improving a vehicle launch from stop. A hybrid vehicle may include an engine as is shown in  FIG. 1 . Additionally, the engine may be included in a driveline of the hybrid vehicle as is shown in  FIG. 2 . The vehicle may launch from stopped conditions as is shown in the sequences of  FIGS. 3 and 4 . The vehicle may include a controller that includes instructions according to the method of  FIG. 5 . 
         [0014]    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  (e.g., low voltage (operated with less than 30 volts) electric machine) includes pinion shaft  98  and pinion gear  95 . Pinion shaft  98  may selectively advance pinion gear  95  to engage ring gear  99 . Starter  96  may be directly mounted to the front of the engine or the rear of the engine. In some examples, starter  96  may selectively supply 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 . 
         [0015]    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 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). 
         [0016]    In addition, intake manifold  44  is shown communicating with turbocharger compressor  162 . 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 air intake  42  to compressor  162  and intake manifold  44 . In one example, 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. 
         [0017]    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 . 
         [0018]    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. 
         [0019]    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 position sensor  154  coupled to brake pedal  150  for sensing force applied by foot  152 , 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  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. 
         [0020]    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. 
         [0021]    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. 
         [0022]      FIG. 2  is a block diagram of a vehicle  225  including a driveline  200 . The driveline of  FIG. 2  includes engine  10  shown in  FIG. 1 . 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 . DISG  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, torque of engine  10  may be adjusted via torque actuator  204 , such as a fuel injector, throttle, etc. 
         [0023]    An engine output torque may be transmitted to an input side of driveline disconnect clutch  236  through dual mass flywheel  215 . Disconnect clutch  236  may be electrically or hydraulically actuated. If disconnect clutch  236  is hydraulically actuated, pump  213  supplies working fluid (e.g., oil) to driveline disconnect clutch  236 . Pump  213  may be incorporated into torque converter  206  or transmission  208 , and pump  213  rotates to supply pressurized working fluid to driveline disconnect clutch  236  and clutches  210 - 211 . Pump  213  is mechanically driven and it rotates to pressurize working fluid when shaft  241  rotates. Pressure at an outlet of pump  213  may be determined via pressure sensor  214 . The downstream side of disconnect clutch  236  is shown mechanically coupled to DISG input shaft  237 . 
         [0024]    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 . 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  (e.g., high voltage battery or power source) 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 . 
         [0025]    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. 
         [0026]    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. 
         [0027]    Automatic transmission  208  includes gear clutches (e.g., gears 1-6)  211  and forward clutch  210 . The gear clutches  211  (e.g., 1-10) 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 . 
         [0028]    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. 
         [0029]    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 field and/or armature windings of DISG as is known in the art. 
         [0030]    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. When engine restart conditions are satisfied, and/or a vehicle operator wants to launch the vehicle, controller  12  may reactivate engine  10  by craning engine  10  and resuming cylinder combustion. 
         [0031]    Thus, the system of  FIGS. 1 and 2  provides for a driveline system, comprising: an engine; an electric machine; an automatic transmission; a torque converter positioned between the automatic transmission and the electric machine; a controller including executable instructions stored in non-transitory memory for applying maximum torque of an electric machine to a torque converter impeller from a condition where electric machine rotation is stopped in response to a driver demand torque less than the maximum torque of the electric machine. The driveline system further comprises additional instructions for reducing electric machine torque to less than the maximum torque of the electric machine from the condition where electric machine rotation is stopped in response to a driver selecting an economy mode. 
         [0032]    In some examples, the driveline system further comprises additional instructions for reducing the maximum torque of the electric machine in response to the torque converter impeller achieving a fluid force transfer speed. The driveline system further comprises additional instructions for applying the driver demand torque to the torque converter turbine via adjusting electric machine speed to a speed that provides the driver demand torque at the torque converter turbine. The driveline system further comprises reducing application of torque to the torque converter impeller from the condition where electric machine rotation is stopped in response to selection of an economy mode. The driveline system further comprises additional instructions for applying the driver demand torque to the torque converter impeller in response to an increase in the driver demand torque when a vehicle in which the electric machine operates is stopped and the electric machine is rotating. 
         [0033]    Referring now to  FIG. 3 , a vehicle launch sequence for a conventional internal combustion engine powertrain is shown along with a vehicle launch sequence for an uncompensated hybrid vehicle. 
         [0034]    The first plot from the top of  FIG. 3  is a plot of torque converter impeller speed, impeller torque, turbine speed, and turbine torque for a conventional powertrain (e.g., internal combustion engine and torque converter, no motor present) versus time. The Y axis arrow indicates a direction for increasing torque converter impeller speed and torque. The Y axis arrow also indicates a direction for increasing torque converter turbine speed and torque. The X axis represents time and time increases from the left side of  FIG. 3  to the right side of  FIG. 3 . Trace  302  represents torque converter turbine torque. Trace  304  represents torque converter impeller speed. Trace  306  represents torque converter impeller torque. Trace  308  represents torque converter turbine speed. 
         [0035]    The second plot from the top of  FIG. 3  is a plot of torque converter impeller speed, impeller torque, turbine speed, and turbine torque for an uncompensated hybrid vehicle powertrain versus time. The Y axis arrow indicates a direction for increasing torque converter impeller speed and torque. The Y axis arrow also indicates a direction for increasing torque converter turbine speed and torque. The X axis represents time and time increases from the left side of  FIG. 3  to the right side of  FIG. 3 . In this example, the uncompensated hybrid vehicle powertrain torque converter impeller torque profile is the same as for the conventional powertrain torque converter impeller. Trace  310  represents torque converter turbine torque. Trace  312  represents torque converter impeller speed. Trace  314  represents torque converter impeller torque. Trace  316  represents torque converter turbine speed. 
         [0036]    At time T 0 , the internal combustion engine of the conventional powertrain is operating at idle speed. Therefore, the torque converter impeller speed and torque converter impeller torque for the conventional powertrain are non-zero and elevated. The torque converter turbine torque for the conventional powertrain is also non-zero and elevated. The torque converter turbine speed for the conventional powertrain is substantially zero. 
         [0037]    The hybrid vehicle&#39;s engine and motor are at zero speed to conserve fuel and electrical charge. Consequently, the torque converter impeller speed and torque converter impeller torque are zero for the hybrid powertrain. Additionally, the torque converter turbine speed and torque converter turbine torque for the hybrid powertrain are also zero. 
         [0038]    At time T 1 , torque is applied to both the torque converter impeller of the conventional powertrain and the torque converter impeller of the hybrid powertrain in response to an increase in driver demand torque (not shown). The torque converter impeller speed, impeller torque, and turbine torque for the conventional powertrain begin to increase almost instantaneously. The torque converter turbine speed for the conventional powertrain does not begin to move. On the other hand, the torque converter impeller speed and torque for the hybrid powertrain begin to increase after a short delay. The torque converter turbine torque increase for the hybrid powertrain is delayed further since the torque converter transfers little torque when the torque converter impeller speed is less than a torque converter fluid force transfer speed. 
         [0039]    At time T 2 , the torque converter turbine torque for the hybrid powertrain begins to increase. The torque converter impeller speed and torque for the hybrid powertrain have increased from zero speed and continue to rise. The torque converter turbine speed for the hybrid powertrain remains at zero since sufficient turbine torque is not present to rotate the torque converter turbine for the hybrid powertrain. 
         [0040]    The rate of rise for the torque converter impeller torque and speed begins to be reduced for the conventional powertrain. The rate of rise for the conventional powertrain torque converter turbine torque also begins to be reduced, but the conventional powertrain torque converter turbine speed begins to increase. 
         [0041]    At time T 3 , the torque converter turbine speed for the hybrid powertrain begins to increase. The rate of rise for the torque converter impeller speed and torque is starting to be reduced for the hybrid powertrain. The torque converter turbine speed for the hybrid powertrain begins to increase in response to the torque converter turbine torque increasing. 
         [0042]    The torque converter turbine torque and speed for the conventional powertrain level off. The torque converter turbine torque also continues to rise. 
         [0043]    The time between time T 1  and time T 3  is the torque delay time for the hybrid powertrain. In this example, the torque delay time is measured from the time the driver increases the driver demand torque until the hybrid powertrain torque converter turbine speed begins to increase. The delay time results from having to accelerate the DISG from zero speed to a speed where the torque converter begins to transfer torque from the torque converter impeller to the torque converter turbine. 
         [0044]    Referring now to  FIG. 4 , a vehicle launch sequence for a conventional internal combustion engine powertrain is shown along with a vehicle launch sequence for an compensated hybrid vehicle. The vehicle launch sequence for the conventional powertrain is the same as is shown in  FIG. 3 . 
         [0045]    The first plot from the top of  FIG. 4  is a plot of torque converter impeller speed, impeller torque, turbine speed, and turbine torque for the conventional powertrain (e.g., internal combustion engine and torque converter, no motor present) versus time. The Y axis arrow indicates a direction for increasing torque converter impeller speed and torque. The Y axis arrow also indicates a direction for increasing torque converter turbine speed and torque. The X axis represents time and time increases from the left side of  FIG. 4  to the right side of  FIG. 4 . Trace  402  represents torque converter turbine torque. Trace  404  represents torque converter impeller speed. Trace  406  represents torque converter impeller torque. Trace  408  represents torque converter turbine speed. 
         [0046]    The second plot from the top of  FIG. 4  is a plot of torque converter impeller speed, impeller torque, turbine speed, and turbine torque for a compensated hybrid vehicle powertrain versus time. The Y axis arrow indicates a direction for increasing torque converter impeller speed and torque. The Y axis arrow also indicates a direction for increasing torque converter turbine speed and torque. The X axis represents time and time increases from the left side of  FIG. 4  to the right side of  FIG. 4 . Trace  410  represents torque converter turbine torque. Trace  412  represents torque converter impeller speed. Trace  414  represents torque converter impeller torque. Trace  416  represents torque converter turbine speed. 
         [0047]    At time T 10 , the internal combustion engine of the conventional powertrain is operating at idle speed. Therefore, the torque converter impeller speed and torque converter impeller torque for the conventional powertrain are non-zero and elevated. The torque converter turbine torque for the conventional powertrain is also non-zero and elevated. The torque converter turbine speed for the conventional powertrain is substantially zero. 
         [0048]    The compensated hybrid vehicle&#39;s engine and motor are at zero speed to conserve fuel and electrical charge. Consequently, the torque converter impeller speed and torque converter impeller torque are zero for the compensated hybrid powertrain. Additionally, the torque converter turbine speed and torque converter turbine torque for the compensated hybrid powertrain are also zero. 
         [0049]    At time T 11 , torque is applied to both the torque converter impeller of the conventional powertrain and the torque converter impeller of the compensated hybrid powertrain in response to driver demand torque (not shown). Full or maximum DISG torque is applied to the torque converter impeller of the compensated hybrid powertrain in response to an increase in driver demand torque. Therefore, the impeller torque of the compensated hybrid powertrain increases faster than the impeller torque of the uncompensated hybrid powertrain shown in  FIG. 3 . The torque converter impeller speed, impeller torque, and turbine torque for the conventional powertrain begin to increase almost instantaneously. The torque converter turbine speed for the conventional powertrain does not begin to move. The torque converter impeller speed for the compensated hybrid powertrain also increases at a faster rate than the torque converter impeller speed for the uncompensated hybrid powertrain shown in  FIG. 3 . The torque converter turbine speed for the compensated hybrid powertrain remains at zero. 
         [0050]    At time T 12 , the torque converter turbine torque for the compensated hybrid powertrain begins to increase. The torque converter impeller speed for the compensated hybrid powertrain continues to rise. The torque converter impeller torque for the compensated hybrid powertrain has reached a peak value and is declining. The torque converter turbine speed for the compensated hybrid powertrain remains at zero since sufficient turbine torque is not present to rotate the torque converter turbine for the hybrid powertrain. 
         [0051]    The rate of rise for the torque converter impeller torque and speed begins to be reduced for the conventional powertrain. The rate of rise for the conventional powertrain torque converter turbine torque also begins to be reduced, and the conventional powertrain torque converter turbine speed remains at zero. 
         [0052]    At time T 13 , the torque converter turbine speed for the compensated hybrid powertrain begins to increase. The rate of rise for the torque converter impeller speed has leveled off and the torque converter impeller torque also levels off for the compensated hybrid powertrain. The torque converter turbine speed for the compensated hybrid powertrain begins to increase in response to the torque converter turbine torque increasing. 
         [0053]    The torque converter turbine speed for the conventional powertrain also begins to increase, and the torque converter turbine torque for the conventional powertrain has leveled off. The torque converter impeller torque and torque converter impeller speed for the conventional powertrain have also leveled off. 
         [0054]    The time between time T 11  and time T 13  is the torque delay time for the compensated hybrid powertrain. The torque delay time is reduced significantly from the torque delay time of the uncompensated hybrid powertrain. Thus, by applying full torque to the DISG in response to an increase in driver demand torque, it may be possible to improve the response of the hybrid powertrain responding from zero speed. 
         [0055]    Referring now to  FIG. 5 , a method for improving launch of a hybrid vehicle is shown. The method of  FIG. 5  may provide the operating sequence shown in  FIG. 4 . Additionally, the method of  FIG. 5  may be included in the system of  FIGS. 1 and 2  as executable instructions stored in non-transitory memory. 
         [0056]    At  502 , method  500  judges if the vehicle is stopped and the vehicle brake is applied. The vehicle may be judged stopped when vehicle speed is zero and the vehicle brake may be judged to be applied in response to an output of a brake pedal position sensor. If method  500  judges that the vehicle is stopped and the brake pedal is applied, the answer is yes and method  500  proceeds to  504 . Otherwise, the answer is no and method  500  proceeds to  503 . In other examples, additional or fewer conditions may be required to be met before method  500  proceeds to  504 . 
         [0057]    If the DISG and engine are rotating when the vehicle is stopped and the brake applied, a torque equivalent to the driver demand based torque may be provided to the torque converter impeller via the DISG or the engine in response to an increase in driver demand torque greater than a first threshold torque and less than a second threshold torque. 
         [0058]    At  503 , method  500  provides a driver demand torque to the torque converter impeller. Further, the transmission gears may be shifted according to a predetermined schedule. Method  500  proceeds to exit after driver demand torque is applied to the torque converter impeller. 
         [0059]    At  504 , method  500  engages first gear and stops the DISG and the engine from rotating. The engine may be stopped by stopping fuel flow and spark to the engine. The DISG may be stopped by stopping current flow to the DISG. Method  500  proceeds to  506  after the engine and DISG have stopped rotating. 
         [0060]    At  506 , method  500  judges if the vehicle brake has been released. Method  500  may judge that the vehicle brake has been released in response to an output of a brake position sensor. Alternatively, or in addition, method  500  may also proceed to  508  in response to the accelerator pedal being applied. If method  500  judges that the vehicle brake has been released, the answer is yes and method  500  proceeds to  510 . Otherwise, the answer is no and method  500  returns to  506 . 
         [0061]    At  508 , method  500  determines the torque converter fluid force transfer speed. In one example, the torque converter fluid force transfer speed is empirically determined and stored to memory and indexed via working fluid (e.g., oil) temperature and impeller input torque. The impeller input torque may be determined via DISG current and/or engine speed and load. The torque converter fluid force transfer speed is an impeller speed below which full DISG torque can be applied to the torque converter impeller without sending an undesirable amount of torque into the transmission. For example, the torque converter may transfer less than five percent of the torque input to the torque converter impeller at impeller speeds less than the torque converter fluid force transfer speed. The torque converter fluid force transfer speed may be less than a base (e.g., warm) engine idle speed. Method  500  indexes the table or function storing the torque converter fluid force transfer speed, determines the torque converter fluid force transfer speed, and proceeds to  510 . 
         [0062]    At  510 , method  500  judges whether or not the accelerator pedal has been applied by more than a threshold amount; however in some examples, method  500  judges if driver demand torque is greater than a first threshold and less than a second threshold. In one example the first threshold may be less than five percent of full scale driver demand torque and the second threshold may be greater than sixty five percent of full scale driver demand torque. Of course, the first and second threshold may be different for different applications. 
         [0063]    Method  500  may judge if an accelerator pedal has been applied based on output of an accelerator pedal position sensor. The accelerator pedal position may be converted in to a driver demand torque based on vehicle speed and accelerator pedal position. If method  500  judges that the accelerator pedal has been applied and driver demand torque has increased by a threshold amount, the answer is yes and method  500  proceeds to  514 . Otherwise, the answer is no and method  500  proceeds to  512 . Alternatively, if method  500  judges that the accelerator pedal or driver demand torque is greater than a first threshold and less than a second threshold, the answer is yes and method  500  proceeds to  514 . Otherwise, the answer is no and method  500  proceeds to  512 . 
         [0064]    At  512 , method  500  enters creep mode by opening the driveline disconnect clutch and rotating the DISG to provide torque sufficient to propel the vehicle at a low speed (e.g., less than 8 KPH) on a flat road. However, if battery state of charge is low, the engine may be started and accelerated to an idle speed such that the engine provides torque sufficient to propel the vehicle at a low speed. Method  500  returns to  510  after the vehicle is placed in creep mode. 
         [0065]    At  514 , method  500  judges if the torque converter impeller speed is less than a torque converter fluid force transfer speed threshold. The fluid force transfer speed may be empirically determined and stored to controller memory as is described at  508 . If method  500  judges that torque converter impeller speed is less than a torque converter fluid force transfer speed threshold, the answer is yes and method  500  proceeds to  516 . Otherwise, the answer is no and method  500  proceeds to  520 . 
         [0066]    At  516 , method  500  supplies full or maximum DISG torque to the torque converter impeller. In some modes, the driveline disconnect clutch may be open when maximum DISG torque is applied to the torque converter impeller. In other examples, the driveline disconnect clutch may be closed when maximum DISG torque is applied to the torque converter impeller. Additionally, in some examples, a fractional amount of maximum DISG torque, but still greater than driver demand based torque, may be applied to the torque converter impeller (e.g., sixty percent of maximum DISG torque) instead of full DISG torque. For example, if a driver selects an economy mode, sixty percent of maximum DISG torque may be provided to the torque converter impeller via the DISG in response to a request for thirty percent of maximum DISG torque. In this way, the DISG torque is not adjusted proportionately with driver demand torque before torque converter impeller speed achieves the torque converter fluid force transfer speed, but is adjusted proportionally with driver demand torque thereafter, in one example. Further, a threshold of thirty percent of maximum DISG torque is particularly advantageous in that enables the appropriate balance between providing driver demanded torque and conserving energy. Thus, as a result, the vehicle&#39;s torque response may be degraded, but electrical energy may be conserved. Method  500  proceeds to  520  after torque greater than driver demand based torque is supplied to the torque converter impeller. 
         [0067]    At  520 , method  500  determines a desired torque converter impeller speed in response to driver demand torque. In one example, the desired torque converter impeller speed is empirically determined and stored to memory. The torque converter impeller speed values stored in memory may be indexed via transmission oil temperature, driver demand torque, and torque converter turbine speed. Alternatively, the steady state torque converter impeller speed may be determined for the driver demand torque and torque converter turbine speed based on the equation: 
         [0000]    
       
         
           
             
               T 
               imp 
             
             = 
             
               
                 ( 
                 
                   
                     N 
                     imp 
                   
                   CF 
                 
                 ) 
               
               2 
             
           
         
       
     
         [0000]    Where T amp  is the torque converter impeller torque, N imp  is the torque converter impeller speed, and CF is the torque converter capacity factor. Method  500  proceeds to  522  after the desired torque converter impeller speed is determined. 
         [0068]    At  522 , method  500  determines torque converter impeller compensation torque based on the present torque converter impeller speed and the desired torque converter impeller speed. In one example, the present torque converter impeller speed is subtracted from the desired torque converter impeller speed to determine a torque converter impeller speed error. The torque converter impeller speed error may be operated on via proportional, derivative, and integral gains to provide a torque adjustment. The proportional, derivative, and integral adjusted amounts may be added together to provide a torque adjustment amount. Method  500  proceeds to  524  after the torque converter impeller compensation torque is determined. 
         [0069]    At  524 , method  500  judges if the torque converter impeller speed is less than the desired torque converter impeller speed determined at  520 . If method  500  judges that actual torque converter impeller speed is less than the desired torque converter impeller speed, the answer is yes and method  500  proceeds to  526 . Otherwise, the answer is no and method  500  proceeds to  530 . 
         [0070]    At  526 , method  500  applies the compensation torque to accelerator pedal based driver demand torque. In one example, the compensation torque determined at  522  is added to driver demand torque that is based on accelerator pedal position. The compensation torque and the accelerator pedal based driver demand torque are delivered by adjusting current supplied to the DISG. Method  500  returns to  520  after the compensation torque and the accelerator pedal based torque are applied to the driveline. 
         [0071]    At  530 , method  500  applies accelerator pedal based driver demand torque to the torque converter impeller. The accelerator pedal based driver demand torque may be provided via adjusting current supplied to the DISG. Method  500  proceeds to exit after the accelerator pedal based driver demand torque is applied to the torque converter impeller. 
         [0072]    In addition, the driveline disconnect clutch may be closed in response to exceeding the torque converter fluid force transfer speed threshold at  514 . The driveline disconnect clutch may be closed to start the engine so that additional torque may be provided to the driveline. Engine torque may be increased so that the driveline may provide the requested accelerator based driver demand torque. Further, gear clutches may be engaged in response to exceeding the torque converter fluid force transfer speed threshold at  514  since the transmission oil pump may develop sufficient pressure to close the driveline disconnect clutch and gear clutches at speed greater than the torque converter fluid force transfer speed threshold. 
         [0073]    Thus, the method of  FIG. 5  provides for a driveline method, comprising: applying a torque via a driveline integrated starter/generator (DISG) to a torque converter impeller from a condition where DISG rotation is stopped in response to a driver demand torque greater that a first threshold and less than a second threshold, the torque at least thirty percent greater than the driver demand torque. The method includes where the first threshold is less than five percent of a maximum driver demand torque. The method includes where the torque is applied until a predetermined DISG speed that is lower than a base engine idle speed is exceeded. 
         [0074]    In some examples, the method includes where the DISG is mechanically coupled to the torque converter impeller. The method further comprises applying maximum DISG torque in response to driver demand torque exceeding the first threshold. The method further comprises reducing DISG torque to less than the torque that is at least thirty percent greater than the driver demand torque from the condition where DISG rotation is stopped in response to a driver selecting an economy mode. 
         [0075]    In another example, the method of  FIG. 5  provides for a driveline method, comprising: applying a first torque via a driveline integrated starter/generator (DISG) to a torque converter impeller from a condition where DISG rotation is stopped in response to a driver demand torque greater than a first threshold and less than a second threshold, the first torque at least thirty percent greater than the driver demand torque; and applying a second torque via the DISG to the torque converter impeller from a condition where the DISG is rotating and a vehicle in which the DISG operates is stopped in response to the driver demand torque greater than the first threshold and less than the second threshold, the second torque substantially equivalent (e.g., within ±5 percent of the commanded value) to the driver demand torque. 
         [0076]    In some examples, the method includes where the second torque substantially equivalent to the driver demand torque is a torque with ±5 percent of the driver demand torque. The method further comprises reducing the first torque in response to the torque converter impeller achieving a fluid force transfer speed. The method includes where the fluid force transfer speed is a speed where maximum DISG torque may be applied to the torque converter impeller without providing more than a threshold level of torque to a transmission input shaft. The method includes where the DISG speed is at or less than a base engine idle speed when the vehicle in which the DISG operates is stopped. The method includes where the first threshold is greater than five percent of a maximum driver demand torque. The method further comprises applying maximum DISG torque in response to driver demand torque exceeding the first threshold when applying the first torque. The method further comprises reducing DISG torque to less than the first torque that is at least thirty percent greater than the driver demand torque from the condition where DISG rotation is stopped in response to a driver selecting an economy mode. 
         [0077]    As will be appreciated by one of ordinary skill in the art, the methods described in  FIG. 5  may represent one or more of any number of processing strategies such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. As such, various steps or functions illustrated may be performed in the sequence illustrated, in parallel, or in some cases omitted. Likewise, the order of processing is not necessarily required to achieve the objects, features, and advantages described herein, but is provided for ease of illustration and description. Although not explicitly illustrated, one of ordinary skill in the art will recognize that one or more of the illustrated steps or functions may be repeatedly performed depending on the particular strategy being used. Further, the described actions, operations, methods, and/or functions may graphically represent code to be programmed into non-transitory memory of the computer readable storage medium in the engine control system. 
         [0078]    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.