Abstract:
An engine control system for regulating a torque output of a variable displacement engine includes a first module that calculates a torque modification term based on an engine operating parameter and a second module that determines a desired engine torque and an estimated engine torque. A third module modifies the desired engine torque based on the torque modification term to provide a modified desired engine torque and a fourth module regulates an engine torque output based on the modified desired engine torque and the estimated engine torque when the engine is operating in a deactivated mode.

Description:
FIELD OF THE INVENTION 
     The present invention relates to displacement on demand (DOD) internal combustion engines, and more particularly to extending operation of a DOD engine in a deactivated mode. 
     BACKGROUND OF THE INVENTION 
     Internal combustion engines generate drive torque that is transferred to a drivetrain via a crankshaft. 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 (i.e., one or more cylinders not active). 
     The engine is controlled using a torque control system that regulates engine operating parameters including, but not limited to, airflow into the engine, electronic spark timing, fueling and the activation or deactivation of the cylinders. The torque control system regulates these engine operating parameters based on the various engine operation inputs and a driver requested engine torque. 
     In existing torque control systems, various sub-systems regulate engine operation. For example, the throttle controls engine intake manifold pressure (i.e., air load) and airflow, the electronic spark control controls the spark timing and fuel injectors meter fueling. In combination, these sub-systems regulate the engine torque output. Assuming that fueling is fixed at a stoichiometric ratio for emissions control, fueling cannot be used to control torque in a normal operating mode. This leaves airflow, air load and spark timing as the sub-systems that can regulate engine output torque. 
     Some engines implement a spark knock limit (i.e., a maximum spark advance that keeps the engine from knocking) that is determined based on cylinder air load. In a deactivated mode, high cylinder air loads are achieved and the spark timing is greatly retarded to prevent knock. As the spark timing is retarded further from the maximum spark for best torque value (MBT), the engine&#39;s torque output decreases. As a result, the throttle is opened to increase the load in order to keep the engine torque output constant. However, as the throttle opens, air load is increased and the spark timing is further retarded. This cycle continues until the engine is fully un-throttled and must return to the activated mode (i.e., operating on all cylinders). At this point, any efficiency gains that result from operating in the deactivated mode are lost. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention provides an engine control system for regulating a torque output of a variable displacement engine. The engine control system includes a first module that calculates a torque modification term based on an engine operating parameter and a second module that determines a desired engine torque and an estimated engine torque. A third module modifies the desired engine torque based on the torque modification term to provide a modified desired engine torque and a fourth module regulates an engine torque output based on the modified desired engine torque and the estimated engine torque when the engine is operating in a deactivated mode. 
     In another feature, the third module modifies the estimated engine torque to provide a modified estimated engine torque. The fourth module regulates the engine torque output based on the modified estimated engine torque. 
     In another feature, the torque modification term includes one of a torque gain and a torque offset. 
     In another feature, the engine operating parameter includes one of a spark timing and a cam phaser position. 
     In another feature, the fourth module regulates the engine torque output based on the desired engine torque and the estimated engine torque when the engine is operating in an activated mode. 
     In other features, the engine control system further includes a fifth module that regulates operation of a vehicle system based on the estimated engine torque while the fourth module regulates the engine output torque based on the modified desired engine torque and a modified estimated engine torque during engine operation in the deactivated mode. The vehicle system includes a transmission. 
     In still another feature, the desired engine torque is determined based on an accelerator pedal input. 
     In yet another feature, the estimated engine torque is determined based on engine operating parameters. 
     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 exemplary engine system that is regulated based on the DOD torque control of the present invention; 
         FIG. 2  is a flowchart illustrating exemplary steps executed by the DOD torque control of the present invention; 
         FIG. 3  is a graph illustrating an extended DOD gain that is achieved using the DOD torque control of the present invention; and 
         FIG. 4  is a functional block diagram of exemplary modules that execute the DOD torque control of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     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, 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. 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). 
     Referring now to  FIG. 1 , a vehicle  10  includes an engine  12  that generates drive torque. Air flows into the engine  12  through a throttle  14 . The engine  12  includes N cylinders  18 . One or more of the cylinders  18  are selectively deactivated during engine operation. Although  FIG. 1  depicts eight cylinders (N=8), 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  and is combusted with fuel in the cylinders  18 . The combustion process reciprocally drives pistons (not shown) within the cylinders  18 . The pistons rotatably drive a crankshaft (not shown) to provide drive torque to the powertrain. The engine  12  can also include intake and/or exhaust cam phasers  22 ,  24 , respectively that adjust the timing of intake and exhaust valve opening relative to the position of the piston within the cylinder (i.e., crankshaft angle). In this manner, the cam phasers  22 ,  24  can regulate the amount of charge air that is trapped in the cylinder as well as the amount of exhaust gas exhausted from the cylinder. 
     A control module  38  communicates with the engine  12  and various inputs and sensors as described herein. A vehicle operator manipulates an accelerator pedal  40  to regulate the throttle  14 . More particularly, a pedal position sensor  42  generates a pedal position signal that is communicated to the control module  38 . 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. The control module  38  determines a control or desired engine torque output (T DES ) based on the pedal position signal. The control module  38  also calculates an actual or estimated engine torque output (T EST ) and regulates the engine torque output using a closed-loop control (e.g., PID control) based on T DES  and T EST . 
     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. 
     The engine load is determined based on the intake MAP, cylinder mode and engine RPM. More particularly, if the MAP 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 the MAP 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. 
     The DOD torque control of the present invention reduces the sensitivity of the torque control due to the knock-limitedness of the engine  12  and the throttle opening tendency to extend engine operation in the deactivated mode. More specifically, if the engine  12  is not operating in the deactivated mode, T DES  and T EST  are determined as normal. For example, T DES  can be calculated based on engine operating parameters including, but not limited to engine RPM, MAP, spark timing, cam phaser position, as well as the driver&#39;s input via the accelerator pedal  40 . T EST  is determined based on a pre-programmed mathematical model based on the above-identified engine operating parameters. If the engine  12  is operating in the deactivated mode, a torque modification term or terms are determined and T DES  is modified based on the torque modification term(s) to provide a modified control or desired torque (T′ DES ). 
     The modification term(s) is/are determined from a look-up table or a plurality of look-up tables based on engine operating parameters including, but not limited to, the ignition timing (i.e., spark advance) and/or the intake and/or exhaust cam phaser position. The modification term(s) include a gain, an offset or both a gain and an offset. For example, T′ DES  can be determined by multiplying T DES  by a gain, by subtracting/adding a torque offset to T DES  or by multiplying T DES  by a gain and subtracting/adding a torque offset. 
     In the deactivated mode, the DOD torque control performs closed-loop torque control based on T′ DES  and T′ EST . The DOD torque control concurrently uses T EST  (i.e., the unmodified actual or estimated engine torque) for parallel running algorithms. For example, T EST  can be used to regulate transmission line pressure during a gear shift, while T′ EST  is concurrently used to regulate engine torque output. 
     Referring now to  FIG. 2 , exemplary steps that are executed by the engine torque control system will be described in detail. In step  200 , control determines whether the engine is operating in the deactivated mode. If the engine is not operating in the deactivated mode, control continues in step  202 . If the engine is operating in the deactivated mode, control continues in step  204 . In steps  202  and  206 , control calculates T DES  and T EST  in a traditional manner. In step  208 , control executes the closed-loop torque control based on T DES  and T EST , and control ends. 
     In step  204 , control determines the modification term(s) based on engine operating parameters including, but not limited to, spark timing and/or cam phaser position. In step  210 , control calculates T DES  and T EST  in a traditional manner. In step  212 , control determines T′ DES  and T′ EST  based on T DES , T EST  and the modification term(s). In this manner, T EST  is calculated in parallel for external algorithm use (e.g., transmission control) and to ensure that the closed-loop torque control is not affected by the modification. In step  208 , control executes the closed-loop torque control based on T′ DES  and T′ EST , and control ends. In this manner, the closed-loop torque control is based on T′ DES  and T′ EST  when operating in the deactivated mode and is based on T DES  and T EST  when operating in the activated mode. 
     Referring now to  FIG. 3 , a graph illustrates an extended DOD gain that is achieved using the DOD torque control of the present invention. More specifically, the DOD torque control extends engine operation in the deactivated mode by regulating the engine torque output based on T′ DES , which remains below the deactivated mode torque threshold (i.e., the torque at which engine operation transitions to the activated mode) for a longer period of time than would be possible if regulating the engine torque output based on T DES . In this manner, a significant portion of the normal distribution of a driver torque request is gained while operating in the deactivated mode and a corresponding increase in fuel economy is achieved by extending operation in the deactivated mode. 
     Referring now to  FIG. 4 , exemplary modules that execute the DOD torque control will be described in detail. The exemplary modules include a modification term module  400 , a T DES  and T EST  determining module  402 , a modification module  404 , a torque control module  406  and a vehicle system control module  408 . The modification term module  400  determines a modification term or terms (e.g., a torque offset and/or gain) based on engine operating parameters (e.g., spark timing and/or cam phaser position). The modification term(s) is/are output to the modification module  404 . The T DES  and T EST  determining module  402  determines T DES  and T EST  based on engine operating parameters (e.g., MAP, RPM and/or accelerator pedal position) and outputs T DES  and T EST  to the modification module  404 . T EST  is also output to the vehicle system control module  408 . 
     The modification module  404  modifies T DES  and T EST  based on the modification term(s) and an activated (ACT) or deactivated (DEACT) signal to provide T′ DES  and T′ EST . More specifically, if the modification module  404  receives the DEACT signal (i.e., engine is operating in the deactivated mode), the modification module  404  outputs T′ DES  and T′ EST  to the torque control module  406 . If the modification module  404  receives the ACT signal (i.e., engine is operating in the activated mode), the modification module  404  outputs T DES  and T EST . It is alternatively anticipated that the modification term module  400  can receive the ACT/DEACT signals. If the modification term module  400  receives the ACT signal, the modification term(s) is/are set to 0, if an offset, and/or is set to 1, if a gain. In this manner, the modification term does not affect T DES  or T EST  in the modification module  404  while the engine is operating in the activated mode. 
     The torque control module  406  generates engine control signals based on T DES  and T EST , if the engine is operating in the activated mode, or T′DES and T′ EST , if the engine is operating in the deactivated mode. The vehicle system control module  408  generates vehicle system control signals based on T EST . The controlled vehicle system can include a transmission, for example. 
     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.