Abstract:
An engine control system in a vehicle including a variable displacement internal combustion engine, a controller for controlling the displacement of the variable displacement internal combustion engine, where the controller adaptively determines a torque threshold used to switch the variable displacement internal combustion engine between a partially displaced operating mode and a fully displaced operating mode.

Description:
TECHNICAL FIELD 
     The present invention relates to the control of internal combustion engines. More specifically, the present invention relates to a method and apparatus to control a variable displacement internal combustion engine. 
     BACKGROUND OF THE INVENTION 
     Regulatory conditions in the automotive market have led to an increasing demand to improve fuel economy and reduce emissions in current vehicles. These regulatory conditions must be balanced with the demands of a consumer for high performance and quick response from a vehicle. Variable displacement internal combustion engines (ICEs) provide for improved fuel economy and torque on demand by operating on the principal of cylinder deactivation. During operating conditions that require high output torque, every cylinder of a variable displacement ICE is supplied with fuel and air (also spark, in the case of a gasoline ICE) to provide torque for the ICE. During operating conditions at low speed, low load, and/or other inefficient conditions for a fully displaced ICE, cylinders may be deactivated to improve fuel economy for the variable displacement ICE and vehicle. For example, in the operation of a vehicle equipped with an eight cylinder variable displacement ICE, fuel economy will be improved if the ICE is operated with only four cylinders during low torque operating conditions by reducing throttling losses. Throttling losses, also known as pumping losses, are the extra work that an ICE must perform when the air filling the cylinder is restricted by a throttle plate during partial loads. The ICE must therefore pump air from the relatively low pressure of an intake manifold through the cylinders and out to the atmosphere. The cylinders that are deactivated will not allow air flow through their intake and exhaust valves, reducing pumping losses by allowing the active cylinders to operate at a higher intake manifold pressure. 
     In past variable displacement ICEs, the switching or cycling between the partial displacement mode and the full displacement mode was problematic. Frequent cycling between the two operating modes negates fuel economy benefits and affects the driveability of a vehicle having a variable displacement ICE. The operator&#39;s driving habits will affect the number of times a variable displacement ICE will cycle between the partial and the full displacement operating modes, and the fuel economy benefits of a variable displacement ICE. Frequent cycling will also impact component life in a variable displacement ICE. 
     SUMMARY OF THE INVENTION 
     The present invention is a method and apparatus for the control of cylinder deactivation in a variable displacement engine. In the preferred embodiment of the present invention, an eight-cylinder internal combustion engine (ICE) may be operated as a four-cylinder engine by deactivating four cylinders. The cylinder deactivation occurs as a function of the load, as determined from engine vacuum or engine torque, required by the vehicle and driver behavior. According to the present invention, the activation and deactivation thresholds that are dependent on the magnitude and frequency of calculated torque requests are adaptively modified to eliminate busyness or unnecessary switching between an activated and deactivated state for the variable displacement ICE. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagrammatic drawing of the control system of the present invention. 
         FIG. 2  is a flowchart of a method of the present invention. 
         FIG. 3  is a flowchart of the initialization of variables used by the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  is a diagrammatic drawing of the vehicle control system  10  of the present invention. The control system  10  includes a variable displacement ICE  12  having fuel injectors  14  and spark plugs  16  (in the case of a gasoline engine) controlled by an engine or powertrain controller  18 . The ICE  12  crankshaft  21  speed and position are detected by a speed and position detector  20  that generates a signal such as a pulse train to the engine or powertrain controller  18 . The ICE  12  may comprise a gasoline ICE, or any other ICE known in the art. An intake manifold  22  provides air to the cylinders  24  of the ICE  10 , the cylinders having valves  25 . The valves  25  are further coupled to an actuation apparatus  27  such as used in an overhead valve or overhead cam engine configuration that may be physically coupled and decoupled to the valves  25  to shut off air flow through the cylinders  24 . An air flow sensor  26  and manifold air pressure (MAP) sensor  28  detect the air flow and air pressure within the intake manifold  22  and generate signals to the powertrain controller  18 . The airflow sensor  26  is preferably a hot wire anemometer and the MAP sensor  28  is preferably a strain gauge. 
     An electronic throttle  30  having a throttle plate controlled by an electronic throttle controller  32  controls the amount of air entering the intake manifold  22 . The electronic throttle  30  may utilize any known electric motor or actuation technology in the art including, but not limited to, DC motors, AC motors, permanent magnet brushless motors, and reluctance motors. The electronic throttle controller  32  includes power circuitry to modulate the electronic throttle  30  and circuitry to receive position and speed input from the electronic throttle  30 . In the preferred embodiment of the present invention, an absolute rotary encoder is coupled to the electronic throttle  30  to provide speed and position information to the electronic throttle controller  32 . In alternate embodiments of the present invention, a potentiometer may be used to provide speed and position information for the electronic throttle  30 . The electronic throttle controller  32  further includes communication circuitry such as a serial link or automotive communication network interface to communicate with the powertrain controller  18  over an automotive communications network  33 . In alternate embodiments of the present invention, the electronic throttle controller  32  may be fully integrated into the powertrain controller  18  to eliminate the need for a physically separate electronic throttle controller. 
     A brake pedal  36  in the vehicle is equipped with a brake pedal sensor  38  to determine the braking frequency and/or amount of pressure generated by an operator of the vehicle on the brake pedal  36 . The brake pedal sensor  38  generates a signal to the powertrain controller  18  to determine a braking condition for the vehicle. A braking condition will indicate a low torque/low demand condition for the variable displacement ICE  12 . An accelerator pedal  40  in the vehicle is equipped with a pedal position sensor  42  to sense the position and rate of change of the accelerator pedal  40 . The pedal position sensor  42  signal is also communicated to the powertrain controller  18 . In the preferred embodiment of the present invention, the brake pedal sensor  38  is a strain gauge and the pedal position sensor  42  is an absolute rotary encoder. 
     The present invention addresses the problems of busyness or high frequency switching between a partial displacement and a full displacement of the variable displacement ICE  10 . In past variable displacement ICEs, the switching or cycling between the partial displacement mode and the full displacement mode was problematic. Frequent cycling between the two operating modes negates fuel economy benefits and effects the drivability of a vehicle having a variable displacement ICE. Frequent cycling will also impact component life in a variable displacement ICE. The switching thresholds are calibrated on an engine dynamometer, but no two vehicles are the same and the variable displacement ICE  10  will behave differently under different environmental conditions. 
     Referring to  FIG. 2 , an initialization method of the present invention is illustrated. Upon engine start, Block  130  is executed, initializing the variables used by the adaptive threshold logic as follows: the variable Running_on_all_cylinders is set to TRUE, the variable First_pass_reac is set to FALSE, the variable First_pass_deac is set to TRUE, and the variable Time_in_deac is set to zero. 
     Referring to  FIG. 3 , the adaptive threshold logic of the present invention is executed following the completion of the standard threshold detection logic described in U.S. Ser. No. 10/104,111, which is hereby incorporated by reference in its entirety. The method begins at block  100 , which determines whether the system is Running_on_all_cylinders. If block  100  is false, then the ICE  12  is operating in the “deactivated” or partially displaced operating mode and block  102  is executed. If block  100  is true, then the ICE  12  is operating in the “reactivated” or fully displaced operating mode and block  116  is executed. At block  102 , the variable Time_in_deac, representing the time spent in a deactivated mode, is incremented by the sampling rate of the present method (Ts) in the controller  18 . Following block  102 , block  104  is executed to determine whether this is the first pass/execution of the method since the ICE  12  entered a deactivated mode. If block  104  is false, block  124  is executed and the method is exited; otherwise, if block  104  is true, block  106  is executed. At block  106 , the variable Time_between_deacs, representing the time between deactivations, is calculated as the difference between the current time as read from a hardware timer/clock in the ECU, and the time of the last deactivation. Following block  106 , block  108  is executed and the variable last deac_time, representing the last deactivation time, is set to the run_time from the controller  18  hardware. Following block  108 , block  109  is executed, block  109  sets the flags First_pass_reac to TRUE and First_pass_deac to FALSE so as to be able to detect the first pass or execution of the method after the ICE  12  enters the reactivated mode. Following block  109 , block  110  is executed to determine if the Time_between_deacs is less than a calibrated threshold, Deac_time_deac_thresh. If block  110  is false, block  124  is executed and the method is exited; otherwise, block  112  is executed. In block  112  the variable Deactivation_threshold, representing the torque value or vacuum level at which the standard threshold detection logic switches from fully displaced mode to partially displaced mode, is decremented by the precalibrated amount Deactivation_delta_cal. 
     The calibration variable, Deactivation − delta_cal, is set as a compromise. If set relatively large, the system will not readily enter a deactivated mode the next time the logic checks to see if ICE  12  should be in a deactivated mode. If set relatively small, the standard detection logic will once again set ICE  12  in a deactivated mode for too short of a time. The result is a rapid switching from a fully displaced operating mode to a partially displaced or deactivated operating mode. Should this occur, the method of  FIG. 4  would once again decrease the threshold and make it even more difficult to enter a deactivated mode. This would continue until the ICE  12  no longer switched rapidly between fully displaced and partially displaced operating modes. Following block  112 , block  114  is executed, restricting the final threshold to be between some calibrated minimum and maximum values. After block  114  is executed, block  124  is executed and the method is exited. 
     Returning to the start of the method of  FIG. 3 , if block  100  is true, then the ICE  12  is in a reactivated mode and block  116  is executed. Block  116  determines if this is the first pass or execution of the present method since the ICE  12  entered a reactivated mode. If false, block  124  is executed and the method is exited. Block  116  determines if the flag First_pass_reac is true, indicating that this is the first time the ICE  12  has been reactivated to operate in a fully displaced mode. If block  116  is true, then block  118  is executed. Block  118  determines if the output of block  102  (Time_in_deac) is greater than a calibrated variable, Deac_time_inc_thresh. If block  118  is false, block  124  is executed and the method is exited; otherwise, if block  118  is true, block  120  is executed. At block  120 , the variable Deac_threshold is incremented by the calibration variable Reactivation_delta_cal. This calibration value is set to be a relatively small fraction of the calibration variable Deactivation_delta_cal_used in block  112 . 
     The purpose of block  120  is to make it less difficult to enter the deactivated mode after each time that a deactivated mode was successfully maintained for a long period of time. The Reactivation_delta_cal in block  118  inhibits block  112  from making it difficult to enter a deactivated mode by providing a mechanism, such that if a deactivated mode is entered for a suitably long time, it is slightly easier to enter the deactivated mode. Blocks  112  and  120  counterbalance each other so that the minimum or maximum threshold limits of block  114  would only be achieved under extremely rare conditions. After block  120 , block  122  is executed, block  123  sets the flags First_pass_reac to false and First_pass_deac to true, so as to be able to detect the first pass or execution of the method after the ICE  12  enters the deactivated mode. Following block  120 , block  122  is executed. At block  122  the variable Time_in_deac is reset to zero, in preparation for the next deactivated event. Following block  122 , block  114  is executed restricting the final threshold value, Deac_torq_threshold, to be between some calibrated minimum and maximum values. After block  114  is executed, block  124  is executed and the method is exited. 
     While this invention has been described in terms of some specific embodiments, it will be appreciated that other forms can readily be adapted by one skilled in the art. Accordingly, the scope of this invention is to be considered limited only by the following claims.