Abstract:
A method for operating an engine in a vehicle includes measuring a current to or from a generator mechanically coupled with the engine and determining at least one operating parameter of the engine. The method also includes providing an amount of fuel to the engine based on the current and the at least one operating parameter.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of application Ser. No. 12/421,023, filed Apr. 9, 2009, which is hereby incorporated by reference herein. 
    
    
     BACKGROUND 
     Certain techniques are known for controlling an automotive vehicle engine. As an example, U.S. Pat. No. 7,182,065 discloses a method for selectively adjusting an amount of fuel to an engine in a vehicle. The method includes providing an amount of fuel to the engine based on a desired output of the engine. An electric machine is commanded to control the engine speed based on driver input. An output error of the engine is determined based on the command to the electric machine. The amount of fuel provided to the engine is adjusted when at least one predetermined condition is met, including the output error of the engine being greater than a predetermined amount. 
     SUMMARY 
     A method for operating an engine in a vehicle includes measuring a current to or from a generator mechanically coupled with the engine and determining at least one operating parameter of the engine. The current is indicative of an actual torque output by the engine. The at least one operating parameter is indicative of an expected torque output by the engine. The method also includes providing an amount of fuel to the engine based on the current and the at least one operating parameter. 
     A method for operating an engine in a vehicle includes determining a measured torque output by the engine, determining an expected torque output by the engine, and providing an amount of fuel to the engine based on a ratio of the measured to expected torques. 
     An automotive vehicle includes an engine and an electric machine mechanically coupled with the engine. The vehicle also includes at least one controller configured to command an amount of fuel to the engine based on a current to or from the electric machine and at least one operating parameter of the engine. 
     While example embodiments in accordance with the invention are illustrated and disclosed, such disclosure should not be construed to limit the invention. It is anticipated that various modifications and alternative designs may be made without departing from the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic representation of a portion of an embodiment of an automotive vehicle. 
         FIG. 2  is an example plot of indicated torque versus air/fuel ratio for an engine of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to  FIG. 1 , an embodiment of an automotive vehicle  10  includes an engine  12  and an electric machine, or generator  14 . The engine  12  and the generator  14  are connected through a power transfer unit, which in this embodiment is a planetary gear set  16 . Of course, other types of power transfer units, including other gear sets and transmissions, may be used to connect the engine  12  to the generator  14 . The planetary gear set includes a ring gear  18 , a carrier  20 , planet gears  22 , and a sun gear  24 . In other embodiments, however, the vehicle  10  may a powertrain with any one of several suitable configurations. For example, the vehicle  10  may be exclusively powered by an internal combustion engine, etc. 
     The generator  14  may be used as a motor, outputting torque to a shaft  26  connected to the sun gear  24 . Similarly, the engine  12  may output torque to a shaft  28  connected to the carrier  20 . A brake  30  is provided for stopping rotation of the shaft  26 , thereby locking the sun gear  24  in place. 
     The ring gear  18  is connected to a shaft  34 , which is connected to vehicle drive wheels  36  through a second gear set  38 . The vehicle  10  may include a second electric machine, or motor  40 , which may be used to output torque to a shaft  42 . Other vehicles, however, may have different electric machine arrangements, such as a greater or fewer number of electric machines. In the embodiment of  FIG. 1 , the motor  40  and the generator  14  may both be used as motors to output torque. Alternatively, each may be used as a generator, outputting electrical power to a high voltage bus  44  and to an energy storage device, or battery  46 . 
     The battery  46  of  FIG. 1  is a high voltage battery that is capable of outputting electrical power to operate the motor  40  and the generator  14  when the generator acts as a motor. Other types of energy storage devices and/or energy output devices may also be used with the vehicle  10 . For example, a capacitor may be used, which, like a high voltage battery, is capable of both storing and outputting electrical energy. Alternatively, a fuel cell may be used in conjunction with a battery and/or capacitor to provide electrical power for the vehicle  10 . 
     The motor  40 , the generator  14 , the planetary gear set  16 , and a portion of the second gear set  38  may generally be referred to as a transaxle  48 . A controller, or transaxle control module (TCM)  50 , controls the components of the transaxle  48 , e.g., the generator  14  and motor  40 . In addition to the TCM  50 , the vehicle  10  may also include a second controller, which, in the embodiment of  FIG. 1 , is a combination vehicle system controller and powertrain control module (VSC/PCM)  51 . The VSC/PCM  51  communicates with the TCM  50  and the engine  12 , and also communicates with the transaxle  48  and the battery  46  through a controller area network (CAN)  52 . Although the VSC/PCM  51  is shown as a single, integrated controller, the VSC and PCM may be contained in separate controllers. In addition, other controllers, such as the TCM  50 , could be integrated into the VSC/PCM  51 , so that the functions of each of the controllers shown in  FIG. 1  were carried out by a single hardware device. 
     The various devices controlled by the VSC/PCM  51  may include their own controllers. For example, an engine control unit (ECU) may communicate with the VSC/PCM  51  and may perform control functions on the engine  12 . This ECU may determine engine airflow, spark advance and desired air/fuel ratio needed to achieve a commanded or desired torque target. As known to those of ordinary skill, the desired air/fuel ratio may be determined by various powertrain system requirements which may include cold starting, cold start emissions, warm engine operation, etc. During cold engine operation, however, the actual air/fuel ratio may vary based on fuel volatility. 
     The battery  46  may have a battery control module (BCM) that sends and receives signals to and from the VSC/PCM  51  and the battery  46 . The transaxle  48  may also include one or more controllers configured to control specific components within the transaxle  48 , such as the generator  14  and/or the motor  40 . Such controllers may communicate with both the TCM  50  and the VSC/PCM  51  via the CAN  52 . 
     As discussed above, the generator  14  is configured to control the speed of the engine  12 , i.e., the engine  12  is operated in a speed control mode. As the engine  12  operates, its speed may be monitored by one or more speed sensors (not shown), such that the generator  14  may provide positive or negative torque through the planetary gear set  16  to maintain the speed of the engine  12  approximately constant. The relationship between the generator  14  and the engine  12  provides a mechanism for adjusting the amount of fuel to the engine  12 . 
     As the vehicle  10  is operated, a number of inputs, including driver inputs, may be received, for example, by the VSC/PCM  51  (or any other suitable controller(s)). As an example, an accelerator pedal position and/or a brake pedal position may be monitored in a known fashion, and signals sent to the VSC/PCM  51  to determine desired vehicle outputs. As another example, energy produced or stored by the generator  14  may be monitored in a known fashion, e.g., via a current sensor, and signals sent to the VSC/PCM  51  to determine a measured brake torque output by the engine  12 . A mapping of generator current versus engine brake torque stored in the VSC/PCM  51 , for example, may be used in such a determination. Alternatively, a strain associated with a crankshaft of the engine  12  may be monitored in a known fashion, e.g., a strain gauge, and signals sent to the VSC/PCM  51  to determine a measured brake torque output by the engine  12 . A mapping of crankshaft strain versus engine brake torque stored in the VSC/PCM  51 , for example, may be used in such a determination. (These mappings may be generated via testing under laboratory conditions and/or computer simulation.) Of course, any suitable technique may be used to measure the brake torque output by the engine  12 . As yet another example, mass air and mass fuel to the engine  12  may be monitored in a known fashion, e.g., via sensors, and signals sent to the VSC/PCM  51  to determine an expected brake torque output by the engine  12 . 
     As known to those of ordinary skill, the mass air flow to the engine  12  may be measured directly with an airflow sensor (not shown) or calculated from other sensor measurements; other engine operating parameters, such as spark advance and commanded air fuel/ratio are, of course, also available to the VSC/PCM  51  because they may be required for basic control of the engine  12 . The VSC/PCM  51  (or any other suitable controller(s)) may thus determine the expected brake and indicated torque output by the engine  12  based on, for example, a mapping of the mass air flow, spark advance and commanded air/fuel ratio versus engine speed. (This mapping may, for example, be generated via testing and/or computer simulations.) Any suitable engine operating parameters, however, may be used. 
     The VSC/PCM  51  may break down the desired vehicle output into device-specific signals that may be used to command the various devices and/or communicate with other controllers. For example, based on the desired vehicle output torque, the VSC/PCM  51  may calculate a desired engine torque, which may be sent directly to the engine  12 , or to an intermediate controller, such as an ECU (not shown). Similarly, the VSC/PCM  51 , based at least in part on the driver inputs, may calculate a desired engine speed, and may communicate it to the TCM  50 . The TCM  50  may then provide a command to the generator  14  to control the speed of the engine  12 . 
     Referring now to  FIGS. 1 and 2 , those of ordinary skill will recognize  FIG. 2  as a plot of engine indicated torque (brake torque plus friction and pumping losses) versus air/fuel ratio at a given spark advance and mass air flow to the engine  12 . As known in the art, the shape of the curve may change as the spark advance and/or mass air flow change. Such curves may be generated, for example, by mapping the engine  12  under laboratory conditions. Data related to these curves may be stored in the VCS/PCM  51  (or other suitable controller(s)). 
     As known in the art, the curve illustrated in  FIG. 2  includes a generally linear portion (lean) to the right of stoichiometric conditions and a non-linear portion (rich) to the left of stoichiometric conditions. In the generally linear region, indicated torque and air/fuel ratio are proportional to each other. 
     As discussed above, the VSC/PCM  51  (or other suitable controller(s)) may determine a measured brake torque output by the engine  12 . Accounting for friction and pumping losses in the system, the VSC/PCM  51  may also determine a measured indicated torque output by the engine  12 . In the example of  FIG. 2 , the measured indicated torque output by the engine  12  is equal to 90 ft-lbs, which corresponds to an air/fuel ratio within the engine  12  of 17.0. As also discussed above, the commanded air fuel/ratio to the engine  12  is available to the VSC/PCM  51 . In the example of  FIG. 2 , the commanded air/fuel ratio is equal to 15.1, which corresponds to an expected indicated torque output by the engine  12  of 100 ft-lbs. (That is, the indicated torque expected to be output by the engine  12  given the commanded air/fuel ratio.) Under different operating states of the engine  12 , such as engine start-up, differences may thus arise between the actual and commanded air/fuel ratio (measured and expected indicated output torques). This, of course, may influence the emissions performance of the vehicle  10 . 
     Minimum cold start emissions may be achieved by operating lean of stoichiometry. Excessive lean operation (e.g., from hesitation fuel due to low volatility), especially during cold engine conditions, however, may result in excessive emissions as well as engine roughness. Therefore, there may be a narrow window of operation lean of stoichiometric conditions that the engine  12  needs to operate within to minimize emissions and roughness. 
     The VSC/PCM  51  (or other suitable controller(s)) may alter the amount of fuel provided to the engine  12  based on the above analysis. In the example of  FIG. 2 , the ratio of the measured indicated torque (90 ft-lbs) to the expected indicated torque (100 ft-lbs) is 0.9. This corresponds to an air-fuel ratio that is approximately 12% lean of the target air/fuel ratio of 15.1. The VSC/PCM  51  may, for example, increase the amount of fuel to the engine  12  by approximately 12% (or some other suitable amount, e.g., something less than 12%) thereby reducing the actual air/fuel ratio (increasing measured indicated torque) by approximately 12% in order to approach the commanded air/fuel ratio that is optimum for emissions performance. (Differences in actual air/fuel ratio and commanded air/fuel ratio may thus result in an increase in engine emissions.) 
     In some embodiments, the VSC/PCM  51  may determine whether the difference between the actual air/fuel ratio (measured indicated torque) and the commanded or expected air/fuel ratio (expected indicated torque) is greater than a threshold, e.g., 8%, before altering the amount of fuel provided to the engine  12 . If the threshold is exceeded, the VSC/PCM  51  may then increase (or decrease) the amount of fuel to the engine  12  by some fixed amount or a variable amount that is a function of the difference. Other control scenarios are also possible. 
     While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. The words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.