Abstract:
An engine control system and method incorporates an FSG to reduce engine speed variation for a displacement on demand engine. The control system transitions between a normal operating mode wherein all cylinders of the engine are operating and a cylinder deactivation mode wherein cylinders of the engine are deactivated. The FSG adjusts torque output to said crankshaft to reduce engine speed variation in response to an unrequested change in engine speed. This allows expanded use of cylinder deactivation. Cylinder deactivation allows reduced fuel consumption when the engine and the FSG are used in generator mode.

Description:
FIELD OF THE INVENTION 
     The present invention relates to engine control systems, and more particularly to an engine control system incorporating cylinder deactivation and a flywheel starter generator. 
     BACKGROUND OF THE INVENTION 
     Some internal combustion engines include engine control systems that deactivate cylinders under low load situations. For example, an eight cylinder engine can be operated using four cylinders. When in deactivated mode, the engine is more fuel efficient due to reduced pumping losses. The engine control system deactivates cylinders under light load conditions. For example, light loads occur at steady state cruise when high engine power is not required, and in other situations such as idle and traveling downhill. The engine control system must be able to re-activate the cylinders quickly if the driver or driving conditions require more power than can be delivered in deactivated mode. 
     A flywheel starter generator (FSG) is connected to a crankshaft of the engine and increases available electrical power during vehicle operation. The FSG replaces a conventional starter, generator and flywheel. Various FSG arrangements are discussed in further detail in commonly owned U.S. Pat. No. 6,208,036 and in U.S. Pat. Nos. 6,202,776 and 6,040,634, which are all incorporated by reference. 
     The power output by the FSG can be used to reduce fuel consumption and emissions. In addition, the FSG can improve fuel economy by allowing the engine to shut off when the vehicle is temporarily stopped. When the vehicle accelerates from the temporary stop, the FSG restarts the engine. 
     SUMMARY OF THE INVENTION 
     A control system and method for a displacement on demand engine includes an engine having a crankshaft. A flywheel starter generator (FSG) communicates with the crankshaft. A controller communicates with the engine and the FSG and initiates cylinder deactivation during engine operation. The FSG adjusts torque output to the crankshaft to reduce engine speed variation during cylinder deactivation. 
     In other features, the FSG operates at a predetermined speed based on engine speed. The controller adjusts current to the FSG to increase torque when engine sag is detected. The controller adjusts current to the FSG to decrease torque when engine boost is detected. 
     A control system and method for a vehicle having a displacement on demand engine includes an engine having a crankshaft. A flywheel starter generator (FSG) communicates with the crankshaft. A power converter is associated with the FSG. An engine controller initiates cylinder deactivation during power generation. The FSG operates at a steady state speed and adjusts torque output to the crankshaft to reduce engine speed variation during cylinder deactivation. 
     In other features, the power converter includes a DC to DC converter that communicates with a high voltage bus. A DC to AC inverter communicates with the DC inverter and an outlet plug. 
     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is a functional block diagram of an engine control system that incorporates cylinder deactivation and a flywheel starter generator according to the present invention; 
         FIG. 1A  is a functional block diagram of an exemplary power supply; 
         FIG. 2  is a flowchart illustrating steps for reducing torque variation during cylinder deactivation according to the present invention; 
         FIG. 3  is a flowchart illustrating steps for reducing torque variation during idle while in cylinder deactivation; 
         FIG. 4  is a flowchart illustrating steps for improving fuel efficiency with cylinder deactivation while in generator mode; 
         FIG. 5  is a waveform comparison illustrating vehicle speed as a function of time for engines with various cylinder deactivation and FSG engine configurations; and 
         FIG. 6  is a waveform comparison illustrating vehicle speed as a function of time for engines operating as a stationary generator for various cylinder deactivation and FSG engine configurations. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, activated refers to engine operation using all of the engine cylinders. Deactivated refers to engine operation using less than all of the cylinders of the engine (one or more cylinders not active). 
     Referring now to  FIG. 1 , an engine control system  10  for an engine  12  according to the present invention is shown. A crankshaft  14  of the engine  12  rotates an FSG  20  and a transmission  22 . A position of an accelerator pedal  23  is sensed by an accelerator pedal sensor  25 , which generates a pedal position signal that is output to an engine controller  28 . The engine controller  28  communicates with and controls the engine  12  and the FSG  20 . The FSG  20  is electrically connected to a battery  30  through an inverter  32 . The inverter  32  converts AC current output by the FSG  20  to DC current, which charges the battery  30  and supplies other vehicle electrical loads  33 . A power supply  36  is electrically coupled to the FSG  20  and provides one or more output voltages, such as 110V and/or 220V, for powering AC electronic devices such as computers, televisions and other devices. 
     Referring now to  FIG. 1A , the power supply  36  is shown in further detail. A high voltage bus  24  is electrically connected to a DC to DC converter  26 , which has an output that is connected to a DC to AC inverter  34 . An output of the converter  34  is connected to an outlet plug  38 . Passengers of the vehicle can connect AC electrical devices to the outlet plug  38 . It will be appreciated that the power supply  36  is merely an exemplary implementation and that other configurations may be employed. 
     The FSG  20  is used to smooth transitions into and out of cylinder deactivation. The FSG  20  is also used to reduce steady state disturbances while in the cylinder deactivation mode. The controller  28  operates the FSG  20  as a speed control device at a steady state speed over time based on current engine speed. If the engine  12  tries to alter the steady state speed, the FSG  20  outputs a compensating torque onto the crankshaft  14 , which reduces engine pulsing and smoothes drive-line torque disturbances. The FSG  20  rotates together with the crankshaft  14 . Any unrequested sag (engine torque decrease) or boost (engine torque increase) experienced by the engine  12  in relation to a cylinder deactivation event is compensated with torque generated by the FSG  20 . 
     If control detects an unrequested sag in engine speed, the FSG  20  is operated in a boost mode. In the boost mode, current is output to the FSG  20  to supply torque on the crankshaft  14  in the same direction as the torque of the engine  12 . If control detects an unrequested boost in engine speed, the FSG  20  is operated in a braking mode. In the braking mode, current is transmitted to the FSG to apply an opposing torque on the crankshaft  14 , which slows the rotation of the crankshaft  14 . While reacting to an unrequested engine speed change, the speed of the FSG  20  may increase or decrease speed before returning to a steady state speed. This speed variation of the FSG  20  is minimal. 
     With reference to  FIG. 2 , steps for reducing torque variation  40  using the FSG  20  during cylinder deactivation are illustrated. Torque variation reduction begins with step  42 . In step  44 , control determines whether the engine  12  is operating. If false, control ends in step  48 . If the engine  12  is operating, the controller  28  determines whether a cylinder deactivation transition occurred in step  46 . If false, control loops to step  44 . If engine operation is transitioning into or out of cylinder deactivation, the FSG  20  is operated at engine speed with the crankshaft  14  in step  50 . 
     In step  54 , control determines if an accelerator pedal position has changed. If the accelerator pedal position changed, control loops back to step  44 . If the accelerator pedal position does not change, control determines whether engine deceleration occurs in step  58 . If false, control proceeds to step  62 . If engine deceleration occurs, control applies current to the FSG  20  to increase torque onto the crankshaft  14  in step  60  and control loops to step  44 . In step  62 , control determines whether engine acceleration is detected. If not, control loops to step  44 . If engine acceleration occurs, control applies current to the FSG  20  to decrease torque onto the crankshaft  14  in step  66  and control loops to step  44 . 
     The FSG  20  can also be used during engine idle to smooth engine torque during cylinder deactivation. This capability is used to smooth engine operation and to reduce steady state disturbances during idle while in the cylinder deactivation mode. 
     With reference to  FIG. 3 , steps for reducing torque variation during idle while in deactivated mode using the FSG  20  are illustrated and are generally identified at  80 . Idle torque smoothing begins with step  84 . In step  86 , control determines whether the engine  12  is operating. If false, control ends in step  94 . If the engine  12  is operating, control determines whether the engine  12  is in cylinder deactivation mode in step  88 . If false, control loops to step  86 . If the engine  12  is operating in cylinder deactivation mode, the controller  28  determines whether the engine  12  is operating at idle speed in step  90 . If not, control loops to step  86 . If the engine  12  is operating at idle, the FSG  20  is operated at engine speed with the crankshaft  14  in step  96 . 
     Control determines whether an unrequested engine deceleration is detected in step  100 . If not, control proceeds to step  108 . If an unrequested engine deceleration is detected in step  100 , control applies current to the FSG  20  to increase torque onto the crankshaft  14  in step  104  and control loops to step  86 . In step  108 , control determines whether engine acceleration is detected. If not, control loops to step  86 . If engine acceleration is detected, control applies current to the FSG  20  to decrease torque onto the crankshaft  14  in step  110  and control loops to step  86 . 
     Cylinder deactivation can be employed when the FSG  20  is used in a stationary generator mode to improve fuel efficiency. Referencing  FIG. 4 , steps for improving fuel efficiency with cylinder deactivation while in generator mode are illustrated generally at  120 . Control begins with step  124 . In step  126 , the controller  28  determines whether the generator mode is enabled. If not, control ends in step  128 . If the generator mode is enabled, the FSG  20  is operated at engine speed in step  130 . Skilled artisans will appreciate that a belt driven starter generator may similarly be employed. Control performs AC power generation in step  134  and cylinder deactivation is enabled in step  138 . 
     It will be appreciated that the engine  12  operates at an appropriate speed related to electrical power generation requirements. In this way, the engine  12  operates at idle for minimal electrical power generation requirements and operates at an increased speed for increased power generation. 
     With reference to  FIG. 5 , several waveforms showing vehicle speed and cylinder modes as a function of time are shown. Exemplary vehicle speed data is shown as a function of time at  164 . Cylinder modes without cylinder deactivation or FSG are shown at  166 . Cylinder deactivation only is shown at  168 . Cylinder modes with the FSG  20  enabled are shown at  170 . Cylinder modes with cylinder deactivation and the FSG  20  are shown generally at  172 . The FSG  20  enables cylinder deactivation at idle as shown at  174  when engine off at idle is not possible. As a result, the FSG  20  expands the range of operation for cylinder deactivation thereby conserving fuel. In this way, the FSG  20  enables cylinder deactivation over a wider range of driving conditions. When comparing the firing cylinders of trace  172  (both cylinder deactivation and FSG employed) with the firing cylinders of traces  166 ,  168  and  170 , the lowest amount of firing cylinders over time is realized at trace  172 . Because the FSG may be employed to provide a torque input, a reduced amount of torque generation is needed by the cylinders. As a result, cylinder deactivation may be entered more often while still providing a necessary overall torque output. 
     Referring now to  FIG. 6 , the advantage of incorporating the FSG  20  with cylinder deactivation during the stationary generator mode is illustrated. Vehicle speed data is shown as a function of time. With no cylinder deactivation or FSG used, the activated mode is used at  184 . Cylinder modes when cylinder deactivation is employed without the FSG  20  are shown at  186 . Cylinder modes of a stationary generator with the FSG  20  and without cylinder deactivation is shown at  188 . Cylinder modes with the FSG  20  and cylinder deactivation is shown at  190 . As can be appreciated, cylinder deactivation and the FSG lower fuel consumption when operating as a stationary generator. 
     Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present invention can be implemented in a variety of forms. Therefore, while this invention has been described in connection with particular examples thereof, the true scope of the invention should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification and the following claims.