Abstract:
An engine control system for controlling engine operation in activated and deactivated modes in a displacement on demand (DOD) engine includes an impulse charging device that is disposed upstream of an intake port of a cylinder of the DOD engine and that is operable to regulate air flow into the cylinder. A first module initiates impulse charging to regulate air flow into the cylinder when a desired engine torque output nears a first threshold engine torque output during engine operation in the deactivated mode.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to internal combustion engines, and more particularly to engine control systems that control engine operation in a displacement on demand engine.  
       BACKGROUND OF THE INVENTION  
       [0002]     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 to improve fuel economy by reducing pumping losses. This process is generally referred to as displacement on demand or DOD. Operation using all of the engine cylinders is referred to as an activated mode. A deactivated mode refers to operation using less than all of the cylinders of the engine (one or more cylinders not active).  
         [0003]     In the deactivated mode, there are fewer cylinders operating. As a result, there is less drive torque available to drive the vehicle driveline and accessories (e.g., alternator, coolant pump, A/C compressor). Engine efficiency, however, is increased as a result of decreased fuel consumption (i.e., no fuel supplied to the deactivated cylinders) and decreased engine pumping. Because the deactivated cylinders do not take in air, overall engine pumping losses are reduced. During typical engine operation in the deactivated mode, the engine is switched to the activated mode when the torque demand is greater than a threshold (e.g., approximately 95%) of the maximum torque available in the deactivated mode.  
         [0004]     During the course of normal driving, there are many operating conditions just above the threshold of the deactivated mode torque limit. As a result, there are multiple occurrences of switching to the less fuel efficient activated mode. Once in the activated mode, hysteresis often delays transition back into the deactivated mode. These conditions result in missed opportunities to reduce fuel consumption.  
       SUMMARY OF THE INVENTION  
       [0005]     Accordingly, the present invention provides an engine control system for controlling engine operation in activated and deactivated modes in a displacement on demand (DOD) engine. The engine control system includes an impulse charging device that is disposed upstream of an intake port of a cylinder of the DOD engine and that is operable to regulate air flow into the cylinder. A first module initiates impulse charging to regulate air flow into the cylinder when a desired engine torque output nears a first threshold engine torque output during engine operation in the deactivated mode.  
         [0006]     In one feature, the impulse charging device inhibits air flow into the cylinder for a portion of an intake event.  
         [0007]     In another feature, the impulse charging device includes a high-speed valve that is operable in an open position to enable air flow therethrough and a closed position to inhibit air flow the reth rough.  
         [0008]     In still other features, the engine control system further includes a second module that switches engine operation to the activated mode when the desired engine torque nears a second threshold engine torque during engine operation in the deactivated mode with impulse charging. The second module switches engine operation to the deactivated mode when the desired engine torque is below the first threshold engine torque minus a hysteresis value.  
         [0009]     In yet another feature, the first module ceases impulse charging when the desired engine torque is below the first threshold engine torque.  
         [0010]     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  
       [0011]     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
         [0012]      FIG. 1  is a functional block diagram illustrating an exemplary vehicle powertrain including a displacement on demand (DOD) engine system having an impulse charging system according to the present invention;  
         [0013]      FIG. 2A  is a schematic cross-section of a cylinder of the engine including an impulse charging valve in a closed position;  
         [0014]      FIG. 2B  is the schematic cross-section of the cylinder of the engine including the impulse charging valve in an open position;  
         [0015]      FIG. 3  is a flowchart illustrating the impulse charging control according to the present invention;  
         [0016]      FIG. 4  is an exemplary graph illustrating torque increase achieved using the impulse charging control of the present invention;  
         [0017]      FIG. 5  is a logic diagram illustrating exemplary modules that execute the impulse control of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0018]     The following description of the preferred embodiment 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 operation using all of the engine cylinders. Deactivated refers to operation using less than all of the cylinders of the engine (one or more cylinders not active). As used herein, the term module 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.  
         [0019]     Referring now to  FIG. 1 , a vehicle  10  includes an engine  12  that drives a transmission  14 . The transmission  14  is either an automatic or a manual transmission that is driven by the engine  12  through a corresponding torque converter or clutch  16 . Air flows into the engine  12  through a throttle  13 . The engine  12  includes N cylinders  18 . One or more of the cylinders  18  are selectively deactivated during engine operation. Although  FIG. 1  depicts four cylinders (N=4), it is appreciated that the engine  12  may include additional or fewer cylinders  18 . For example, engines having  4 ,  5 ,  6 ,  8 ,  10 ,  12  and  16  cylinders are contemplated. Air flows into the engine  12  through an intake manifold  20  is directed to the cylinders  18  through runners  22  and is combusted with fuel in the cylinders  18 .  
         [0020]     Referring now to  FIGS. 1, 2A  and  2 B, the engine further includes impulse charging devices  24  located within respective intake runners  22  associated with respective cylinders  18 . Although two impulse charging devices  24  are illustrated, it is appreciated that more or fewer impulse charging devices  24  can be implemented. The impulse charging devices  24  selectively inhibit air flow from the intake manifold into its respective cylinder, as discussed in further detail below. More specifically, each impulse charging device  24  includes a high-speed valve  26 . During normal engine operation, the valve  26  remains open and has very little effect on air intake into the cylinders  18 . In an impulse charging mode, the valve  26  is closed during most of the intake event. As a result, there is a low pressure or vacuum within the cylinder  18  and along the intake runner  22  downstream of the impulse charging device  24 .  
         [0021]     The valve  26  is rapidly opened at a predetermined time towards the end of the intake event and an inrush of air produces a supercharging effect within the cylinder  18 . In this manner, the air pressure above the piston is increased over a traditional intake event. The valve  26  is closed and a positive pressure wave produced by the inrush of air is captured. At the beginning of the subsequent intake event, the positive pressure wave functions to eliminate exhaust residuals. In the impulse charging mode, the torque output of the engine can be increased as much as 20% at lower engine speeds.  
         [0022]     A control module  38  communicates with the engine  12  and various inputs and sensors as discussed herein. An engine speed sensor  48  generates a signal based on engine speed. An intake manifold absolute pressure (MAP) sensor  50  generates a signal based on a pressure of the intake manifold  20 . A throttle position sensor (TPS)  52  generates a signal based on throttle position.  
         [0023]     When light engine load occurs, the control module  38  transitions the engine  12  to the deactivated mode. In an exemplary embodiment, N/2 cylinders  18  are deactivated, although one or more cylinders may be deactivated. Upon deactivation of the selected cylinders  18 , the control module  38  increases the power output of the remaining or activated cylinders  18 . The inlet and exhaust ports (not shown) of the deactivated cylinders  18  are closed to reduce pumping losses.  
         [0024]     The engine load is determined based on various engine operating parameters including, but not limited to, the intake MAP, cylinder mode, impulse charging mode and engine speed. More particularly, engine load is expressed as the percent of maximum available engine torque. For purposes of discussion, engine torque will be used in the foregoing discussion. If engine torque is below a threshold level for a given RPM, the engine load is deemed light and the engine  12  is operated in the deactivated mode. If engine torque is above the threshold level for the given RPM, the engine load is deemed heavy and the engine  12  is operated in the activated mode. An exemplary threshold level is 95% of maximum available torque (T DEAC ). The control module  38  controls the engine  12  based on the impulse charging control to maintain engine operation in the more fuel efficient regions and to extend the time during which the engine  12  operates in the deactivated mode.  
         [0025]     The impulse charging control of the present invention regulates engine operation in the impulse charging mode concurrent to the engine operating in the deactivated mode. More particularly, there is a maximum available engine torque when operating in the deactivated mode (T DEAC ). When the torque demand on the engine (T DES ) exceeds a threshold torque (T THR ) (e.g., 90%-95% of T DEAC ), the deactivated cylinder mode engine is concurrently operated in the impulse charging mode. Impulse charging while operating in the deactivated mode provides an increased available engine torque (T DEACIC ) (i.e., T DEAC &lt;T DEACIC ). In general, a torque increase of up to approximately 20% can be achieved (e.g., T DEACIC =(1.2)T DEAC ).  
         [0026]     T THR  correspondingly increases to provide a second threshold (T THRIC ) when operating in the concurrent deactivated and impulse charging modes. Using an exemplary value of 95%, T THR  would be approximately equal to 0.95*T DEAC  in the deactivated mode T THRIC  would be approximately equal to 0.95*T DEACIC  in the deactivated mode with impulse charging. Because T DEACIC  is greater than T DEAC , T THRIC  in the deactivated mode with impulse charging is greater than T THR  in the deactivated mode without impulse charging. Engine operation switches to the activated mode when the T DES  exceeds T THRIC . More specifically, when T DEACIC  is insufficient to provide T DES , engine operation is switched to the activated mode. T DES  is determined based on driver demand (e.g., accelerator pedal position).  
         [0027]     Referring now to  FIG. 3 , exemplary steps executed by the impulse charging control will be described in detail. In step  100 , control determines whether to transition to the deactivated mode. If control determines not to transition to the deactivated mode, control loops back. If control determines to transition to the deactivated mode, control deactivates select cylinders  18  in step  102 .  
         [0028]     In step  104  control monitors T DES . Control determines whether T DES  exceeds T THR  in step  106 . If T DES  does not exceed T THR , control ends impulse charging if it is currently active in step  108  and loops back to step  104 . If T DES  exceeds T THR , control initiates impulse charging in step  110 . In step  112 , control determines whether T DES  exceeds T THRIC . If T DES  does not exceed T THRIC , control loops back to step  104 . If T DES  exceeds T THRIC , control ends impulse charging activity and activates all cylinders (i.e., switches to the activated mode) in steps  113 ,  114  and ends.  
         [0029]     Referring now to  FIG. 4 , exemplary torque curves versus engine speed are illustrated for the impulse charging control. An exemplary DOD range for the deactivated mode is defined from approximately 950 RPM to approximately 2900 RPM. T DEAC  (in phantom) indicates the torque curve during normal engine operation in the deactivated mode. The T DEACIC  (in solid) indicates the torque curve during engine operation in the deactivated mode with impulse charging. A significant torque increase is achieved by concurrent operation in the deactivated mode and impulse charging modes, enabling the engine to remain in the deactivated mode for an extended period.  
         [0030]     Referring now to  FIG. 5 , the logic flow of the impulse charging control will be described in detail. A cylinder mode module  500  receives engine operating parameters including torque and RPM signals, and generates a cylinder activation or deactivation signal based thereon. The cylinder activation or deactivation signal is sent to a cylinder actuator module  502  and a torque module  504 . The cylinder actuator  502  deactivates or activates selected cylinders based on the activation or deactivation signal. The torque module  504  monitors the available torque output of the engine in comparison to T DES . The torque module  504  generates an impulse charging control signal if T DES  is nearing T THR . The impulse charging control signal is sent to an impulse charging module  506 , which regulates operation of the impulse charging devices  24 .  
         [0031]     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.