Abstract:
A fuel injection system for a direct fuel injection (DFI) engine is provided. The system includes: injection mode module selects a fuel injection mode to be one of a single injection mode and a dual injection mode during DFI engine idle operation based on a torque request; and a fuel injection command module that commands fuel injection events based on a crankshaft position and the fuel injection mode.

Description:
FIELD 
     The present disclosure relates to methods and systems for direct fuel injection engines. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     Controlling the amount of fuel and air to be delivered per cylinder for a four stroke internal combustion engine is important to achieve optimum performance. Proper timing of intake and exhaust valves also provide for better performance. Conventional engines include camshafts that regulate the timing of the valves. The rotation of the camshaft can be controlled to ensure proper timing of each valve. In addition cam phasers may be included to alter the position of the camshafts relative to the crankshaft which provides for further opportunities to properly adjust the timing of each valve. 
     The placement of fuel injectors within the engine and the control of fuel injection timing also impacts engine performance. Port fuel injection engines locate one fuel injector per cylinder, mounted in the intake manifold near the cylinder head. Each injector may be controlled either individually or by groups to inject fuel near the intake valve. Spark-ignited direct injected (SIDI) engines locate one fuel injector per cylinder, mounted directly over the cylinder head. Each injector is controlled individually to inject fuel directly into the cylinder. 
     Conventional methods of controlling fuel during idle conditions, whether in a port fuel injected engine or a SIDI engine, intentionally retard spark timing in order to provide a reserve torque. Spark timing is then advanced when a request for torque is initiated. This allows the engine to respond to load demands (i.e. power steering “cramp” input) during idle operation. Retarding spark at idle provides for sub-optimal efficiency. 
     SUMMARY 
     Accordingly, a fuel injection system for a direct fuel injection (DFI) engine is provided. The system includes: injection mode module selects a fuel injection mode to be one of a single injection mode and a dual injection mode during DFI engine idle operation based on a torque request; and a fuel injection command module that commands fuel injection events based on a crankshaft position and the fuel injection mode. 
     In other features, a fuel injection method for a direct fuel injection (DFI) engine is provided. The method includes: operating the engine in an idle state. During the idle state: commanding fuel at a first rate during a combustion cycle; receiving a request to increase torque; transitioning to a dual injection mode based on the request; and commanding fuel at a second rate and at a third rate during the combustion cycle. 
     Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
         FIG. 1  is a functional block diagram illustrating an internal combustion engine system including direct fuel injection hardware. 
         FIG. 2  is a dataflow diagram illustrating a fuel injection system. 
         FIG. 3  is timing diagrams illustrating the scheduling of fuel injection events during a single injection mode and a dual injection mode. 
         FIG. 4  is a graph illustrating the effects of switching between the single injection mode and the dual injection mode on engine speed and fuel flow rates. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is in no way intended to limit the disclosure, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify the same elements. As used herein, the term module and/or device refers to an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, a combinational logic circuit and/or other suitable components that provide the described functionality. 
     Referring now to  FIG. 1 , an engine system  10  includes an engine  12  that combusts an air and fuel mixture to produce drive torque. Air is drawn into an intake manifold  14  through a throttle  16 . The throttle  16  regulates mass air flow into the intake manifold  14 . Air within the intake manifold  14  is distributed into cylinders  18 . Although a single cylinder  18  is illustrated, it can be appreciated that the engine can have a plurality of cylinders including, but not limited to, 2, 3, 5, 6, 8, 10, 12 and 16 cylinders. 
     A fuel injector  20  is electronically controlled to inject fuel into the cylinder  18 . Fuel is combined with air as it is drawn into the cylinder  18  through the intake port. An intake valve  22  selectively opens and closes to enable the air to enter the cylinder  18 . The intake valve position is regulated by an intake camshaft  24 . A piston (not shown) compresses the air/fuel mixture within the cylinder  18 . A spark plug  26  initiates combustion of the air/fuel mixture, driving the piston in the cylinder  18 . The piston drives a crankshaft (not shown) to produce drive torque. Combustion exhaust within the cylinder  18  is forced out through an exhaust manifold  28  when an exhaust valve  30  is in an open position. The exhaust valve position is regulated by an exhaust camshaft  32 . The exhaust can then be treated in an exhaust system (not shown). Although single intake and exhaust valves  22 , 30  are illustrated, it can be appreciated that the engine  12  can include multiple intake and exhaust valves  22 , 30  per cylinder  18 . 
     A crankshaft sensor  34  senses a position of the crankshaft and generates a crankshaft signal. A control module  36  receives the crankshaft signal, interprets the signal as degrees of rotation and schedules fuel injection events based on the interpretation of the signal. The control module  36  sends a fuel injection signal to the fuel injector to control the amount and the timing of the fuel delivery. The fuel injection signal can be a pulse width modulated signal where the pulse width regulates the amount of fuel delivered to the cylinder. 
     Referring now to  FIG. 2 , the present disclosure provides a control method and system that governs the transitions between single and dual fuel injection modes during idle conditions. A dataflow diagram illustrates various embodiments of the fuel injection system that may be embedded within the control module  36 . Various embodiments of fuel injection systems according to the present disclosure may include any number of sub-modules embedded within the control module  36 . The sub-modules shown may be combined and/or further partitioned to similarly govern the transitions between the single injection mode and the dual injection mode during idle conditions. 
     In various embodiments, the control module  36  of  FIG. 2  includes an injection mode module  50  and a fuel injection command module  52 . The injection mode module  50  receives as input a torque request  54 . As can be appreciated, the inputs to the system may be sensed from the system  10 , received from other control modules (not shown) in the system, or determined from other sub-modules within the control module  36 . The injection mode module  50  selects an injection mode  56  to be one of a single injection mode and a dual injection mode based on the torque request  54 . 
     The fuel injection command module  52  receives as input the injection mode  56  and a crankshaft position  58 . The fuel injection command module  52  schedules fuel injection events and commands fuel  60  based on the injection mode  56  and the crankshaft position  58 . 
     Referring now to  FIG. 3 , timing diagrams for scheduling fuel injection events according to the present disclosure are shown. During engine idle operating conditions, control begins in the single injection mode shown generally at  100 . During the single injection mode, one injection event is scheduled per cylinder per combustion cycle. If during idle conditions, an increase in torque is requested, control switches to a dual injection mode shown generally at  200 . During the dual injection mode, two injection events are scheduled per cylinder per combustion cycle. This generates an increase in torque without increasing fuel consumption. 
     More specifically, fuel injection events can be scheduled according to the crankshaft position indicated by degrees of crank rotation. A crankshaft signal can be interpreted as a position in crank degrees. Each diagram illustrates the position of the crankshaft in crank degrees during a combustion cycle. The combustion cycle includes the piston performing the intake stroke and the combustion stroke. The piston begins the intake stroke at three hundred sixty (360) crank rotation degrees before top dead center at  110 . The piston begins the combustion stroke at one hundred eighty (180) crank rotation degrees before top dead center (also referred to bottom dead center (BDC)) at  120 . The piston ends the combustion stroke at top dead center or zero (0) crank rotation degrees shown at  130 . Firing of spark for both the single injection mode  100  and the dual injection mode  200  occurs near top dead center of the combustion stroke at  140 . In an exemplary embodiment firing occurs between ten (10) and zero (0) crank degrees before top dead center. 
     When in the single injection mode  100 , a single injection event is scheduled early in the combustion cycle. The injection event is scheduled early in the combustion cycle and can be scheduled anywhere between two hundred fifty (250) and three hundred eighty (380) crank degrees before firing of spark. An exemplary range for scheduling the fuel delivery is between two hundred and seventy (270) and three hundred and thirty (330) crank degrees before firing of spark as shown at  150 . The single injection mode  100  delivers less torque than dual injection for the same conditions but allows for spark timing to be near minimum best torque (MBT) to improve efficiency. 
     If an increase in torque is requested, control switches to the dual injection mode  200  and commands two fuel injection events per cylinder per combustion cycle. The first injection event is scheduled early in the combustion cycle and can be scheduled anywhere between two hundred fifty (250) and three hundred eighty (380) crank degrees before firing of spark. An exemplary range for scheduling the first fuel delivery is between two hundred and seventy (270) and three hundred and thirty (330) crank degrees before firing of spark as shown at  160 . The amount of fuel delivered however, is reduced compared to homogeneous operating conditions. In an exemplary embodiment, the amount of fuel delivered is between twenty (20) and ninety (90) percent of the total required fuel for the combustion stroke. 
     The second fuel injection event is scheduled late in the combustion cycle and can be scheduled anywhere between zero (0) and one hundred eighty (180) crank degrees before firing of spark. An exemplary range for scheduling the second fuel delivery is between twenty (20) and ninety (90) crank degrees before firing of spark as shown at  170 . The second injection event injects the remainder of fuel necessary for the combustion cycle. An exemplary amount includes ten (10) to eighty percent (80) of the total fuel required for the combustion stroke. 
     Referring now to  FIG. 3 , a graph illustrates the impact on engine speed and fuel economy when controlling the fuel injection events according to the present method. Engine speed in RPM is shown along the y-axis at  300 . Time in seconds is shown along the x-axis at  310 . Fuel flow rate in g/s is shown along the y-axis at  320 . Dual pulse active data is shown at  330 . Engine speed data is shown at  340 . Fuel flow rate data is shown at  350 . As shown by the data, when the dual injection mode is active, engine speed increases, thus compensating for the increase in load. Fuel flow rate decreases to improve fuel economy. 
     Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present disclosure can be implemented in a variety of forms. Therefore, while this disclosure has been described in connection with particular examples thereof, the true scope of the disclosure 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.