Abstract:
An engine control system in a vehicle including a variable displacement internal combustion engine, an intake manifold coupled to the variable displacement internal combustion engine, a controller for controlling the displacement of the variable displacement internal combustion engine, a pressure sensor sensing manifold pressure, the pressure sensor electronically coupled to the controller, and where the controller receives pressure information from the pressure sensor and changes the displacement of the variable displacement internal combustion engine in response to the pressure information.

Description:
This application claims priority from U.S. Provisional Application No. 60/292,156 filed May 18, 2001. 
    
    
     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 
     Present regulatory conditions in the automotive market have led to an increasing demand to improve fuel economy and reduce emissions in present vehicles. These regulatory conditions must be balanced with the demands of a consumer for high performance and quick response for 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 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 than an ICE must perform to pump air from the relatively low pressure of an intake manifold, across a throttle body or plate, through the ICE 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 forcing the ICE to operate at a higher intake manifold pressure. Since the deactivated cylinders do not allow air to flow, additional losses are avoided by operating the deactivated cylinders as “air springs” due to the compression and decompression of the air in each deactivated cylinder. 
     In past variable displacement ICEs, the switching between a partially displaced and fully displaced operating condition for a variable displacement internal combustion engine was problematic due to the disturbances associated with varying the displacement of the 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 load or torque demand by the vehicle. Torque reserve can be estimated using vacuum pressure determined by subtracting engine manifold pressure from the barometric pressure. As seen in FIG. 1, there is a generally linear relationship between vacuum pressure and reserve engine torque. An engine or power train controller will monitor vacuum pressure and determine if the ICE should enter four-cylinder mode. If the ICE is in a condition where it can deliver the desired torque with partial displacement to improve efficiency, the controller will deactivate the mechanisms operating the valves for the selected cylinders and also shut off fuel to the selected cylinders. The deactivated cylinders will thus function as air springs. 
     Fuel economy for a variable displacement ICE is maximized by operating in a partially displaced mode or configuration. The present invention maximizes the amount of time spent in a partially displaced operation while maintaining the same performance and driveability of a fully displaced ICE. Fuel economy improvement is maximized by entering a partially displaced configuration as quickly as possible, and staying in the partially displaced configuration for as long as possible in the operation of a variable displacement ICE. To make the change from variable to full displacement imperceptible to the driver, the ICE must be able to maintain some torque reserve when partially displaced (as detected by vacuum) to allow the generation of any additional torque that may be requested during the time delay of a switching cycle. The switching cycle requires approximately 1000 engine crank degrees during a change from partial to full displacement or vice versa. Continued switching or cycling (busyness) between partial and full displacement should also be reduced as it will compromise fuel economy and emissions for a variable displacement ICE. 
     The present invention reduces the busyness of operating mode switching or cycling by monitoring the amount of time operating with partial displacement. Busyness is detected if this partial displacement operating time does not exceed a calibrated time, and a non-busy condition is detected if the operating time exceeds a second calibrated time. When operating conditions that generate busyness are detected, the vacuum threshold to switch to partial displacement is incremented by a calibration value to decrease the potential for cycling. Whenever a non-busy condition is detected, the threshold is reduced by a calibrated amount. This allows the system to quickly increase the threshold to reduce cycling and slowly reduce the threshold when busyness is not detected. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a torque versus manifold pressure graph; 
     FIG. 2 is a diagrammatic drawing of the control system of the present invention; 
     FIG. 3 is a graph of the different operating conditions of the present invention; 
     FIG. 4 is a flowchart for busyness detection based on engine vacuum; and 
     FIG. 5 is a flowchart for engine load moding based on engine vacuum. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 2 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 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 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 amount of pressure generated by an operator of the vehicle on the brake pedal  36 . The brake pedal sensor  36  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 of the accelerator pedal. 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. 
     Referring to FIG. 3, partial displacement and full displacement operating mode cycling are based primarily on engine vacuum hysteresis pairs, selected by mode and RPM. FIG. 3 illustrates the relationship between vacuum for the ICE  12  operating in a partially displaced and fully displaced mode or configuration. 
     To reduce the busyness or switching between a partially displaced (preferably four cylinders “V4” operating in an eight cylinder “V8” engine) and fully displaced mode, the busyness must be quantified. FIG. 4 is a flow chart detailing the detection of busyness in the present invention. Starting at block  50 , the routine determines if the engine  10  is in V4 or V8 mode. If the engine  10  is not in V4 mode, the routine continues to block  52  where it is determined if the last mode was V8 mode. If the engine was not in V8 mode the last loop, the LastMode is set to V8 in block  54  and the busyness vacuum offset can be updated based on the time in V4 mode. The counter V4Time is the continuous time (in 12.5 msec loops) spend in V4 mode before switching to V8 mode. If the V4Time is less than the BusyTime_Threshold, as determined in block  56 , the system is determined to be “busy” and the Busyness Vacuum Offset is increased in block  58  by the amount of the calibration, BusyVacuum. If the V4Time is greater than the NotBusyTime Threshold, as determined in block  60 , the system is not busy and the Busyness Vacuum Offset is decreased in block  62  by the amount of the calibration, NotBusyVacuum. The routine will then continue to the engine load moding logic of block  64 . If the LastMode was equal to V8, as determined in block  52 , the routine will then continue to the engine load moding logic of block  64 . 
     If the engine  10  is in V4 mode, as determined at block  50 , then at block  66  the routine will determine if the LASTMODE was V4 mode. If the engine was not in V4 mode in the last loop as determined in block  66 , the LastMode flag is set to V4 in block  70  which allows the routine to initialize the loop counter for V4Time to one loop (12.5 msec) in block  72  and the routine will continue to the engine load moding logic of block  64 . If the LastMode was equal to V4 as determined in block  66 , the loop counter V4TIME is incremented by one loop time and the routine continues to the engine load moding logic of block  64 . The method illustrated in FIG. 4 attempts to maximize the time the ICE  12  is in a partially displaced operating configuration and to reduce busyness. 
     The present invention uses three calibration tables for vacuum thresholds versus engine speed for V8→V4 moding and two calibration tables for V4→V8 moding. If the vacuum exceeds the V8→V4 threshold calibration for a variable consistency time, the engine load is low enough to be commanded to switch to partial displacement. The consistency time varies with the difference between the measured vacuum and the threshold to require longer consistency times when nearer the threshold. When the vacuum is less than the V4→V8 threshold calibration, the engine load is too high for partial displacement, and the engine is commanded to switch to full displacement. 
     FIG. 5 illustrates the engine load moding logic of the present invention. At block  67  the routine determines if the engine  10  is in a V8 operating mode. If the engine  10  is not in a V8 mode, then the routine at block  68  determines if the vehicle is in cruise mode. If the vehicle is not in cruise mode, then at block  70 , if the routine determines the vacuum is less than the Normal_V8_Threshold calibration, it will increment the V8_Consistency_Time in block  72  by one loop time. Then proceeding to block  74 , if the V8_Consistency_Time is determined to exceed a calibration value for Normal_V8_Time_Threshold, the V4_Consistency_Time is set to zero in block  84  and the routine proceeds to block  86  to set the Engine_Load to V8. The routine proceeds to block  130  to check for other V4 mode enable criteria. Returning to block  74 , if the V8_Consistency_Time is determined not to exceed a calibration value for Normal_V8_Time_Threshold, the routine sets the Engine_Load to V4 in block  76  and proceeds to block  130  to check for other V4 mode enable criteria. Returning to block  70 , if the vacuum was determined to not be less than the Normal_V8_Time_Threshold, the routine proceeds to execute the routines in block  76  and  130  described above. Returning to block  68 , if the routine determines that cruise mode is true, the routine proceeds to block  78  where if the vacuum is determined to exceed the calibration for Cruise_V8_Threshold, the routine proceeds to block  70  and executes the routine described above. If in block  78 , the vacuum is determined to not exceed the Cruise_V8_Threshold, the routine increments the V8_Consistency_Time in block  80  and proceeds to block  82 . If the V8_Consistency_Time is determined to exceed the Cruise_V8_Threshold time in block  82 , the routine proceeds to block  84  and executes the routine described above. Otherwise, the routine proceeds to block  76  to execute the routines also described above. 
     Returning to block  67 , if the engine is determined to be in V8 mode, the routine proceeds to block  88  where if the vacuum exceeds the Fast_V4_Threshold+Busyness_Vacuum_Offset vacuum threshold, the routine proceeds to block  120  to set the V8_Consistency_Time to zero and then proceeds to block  76  to run routine described above. Returning to block  88 , if the vacuum does not exceed the threshold, the routine determines if the vacuum exceeds the Normal_V4_Threshold+Busyness_Vacuum_Offset in block  90  and if true, proceeds to block  92  to increment the V4_Consistency_Time by one loop time. Continuing from block  92 , in block  94  if the routine determines that the V4_Consistency_Time exceeds the Normal_V4_Time_Threshold, it then proceeds to block  120  to run the routine described above. Returning to block  94 , if time does not exceed the threshold, the routine proceeds to block  86  to run the routine described above. Returning to block  90 , if the vacuum was determined not to exceed the threshold, the routine proceeds to block  96  and determines if the vacuum does not exceed the cruise vacuum threshold of Cruise_V4_Threshold+Busyness_Vacuum_Offset and proceeds to block  86  as described above. If the vacuum did exceed the threshold in block  96 , the routine increments the V4_Consistency_Time in block  98  and continues to block  100  where it determines if the V4_Consistency_Time exceeds the Cruise_V4_Time_Threshold in block  100 . If true, the routine proceeds to block  110  to set Cruise_Mode to True and then to blocks  120  and  76  as described above. Returning to block  100 , if the time did not exceed the threshold, the routine proceeds to block  86  to run the routine described above. 
     Other operating criteria include entering the V8 operating mode when a large change in accelerator pedal position (a large torque request) has been detected or the accelerator is near a fully depressed value. V4 mode may only be allowed within a calibrated range of voltage, oil pressure, oil temperature, engine speed and coolant temperature in the preferred embodiment of the present invention. Cylinder deactivation faults will also prevent V4 mode operation. To improve launch and driveability, the V4 operating mode may be limited to only high gears. Towing mode, engine protection factors, and certain engine control system component faults may also prevent the V4 operation. 
     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.