Abstract:
An engine control system in a vehicle including a variable displacement internal combustion engine, an intake manifold coupled to the internal combustion engine, a throttle coupled to the intake manifold, a controller for controlling the throttle and the engine, an accelerator pedal having an accelerator pedal accelerator sensor electronically coupled to the controller, and where the controller controls the position of the throttle to maintain a substantially consistent pedal position to generate substantially the same torque for different displacements of the engine, where changes in the displacement of the engine are transparent to the operation or operator of the accelerator pedal.

Description:
TECHNICAL FIELD  
         [0001]    The present invention relates to the control of internal combustion engines. More specifically, the present invention relates to a method and apparatus to provide a consistent relationship between the position of an accelerator pedal and the output torque of a variable displacement internal combustion engine.  
         BACKGROUND OF THE INVENTION  
         [0002]    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 in 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 to pull air around the restriction of a relatively closed throttle plate and pump air from the relatively low pressure of an intake manifold 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.  
           [0003]    In past variable displacement ICEs, when partially displaced, the operator would have to alter the position of an accelerator pedal to produce the same torque as when the ICE is fully displaced. Previous variable displacement ICEs were equipped with conventional pedal-throttle-wire couplings that required different accelerator pedal positions for the operation of a fully-displaced ICE and a partially-displaced ICE. The physical coupling between the accelerator pedal and throttle, and the inability to control throttle position as a function of displacement in previous variable displacement ICEs, prevented compensation in the accelerator pedal position for changes in output torque. The amount of air flow through the throttle required to generate the same torque for a fully-displaced and partially-displaced operation was different, requiring the physical position of the throttle plate and accelerator pedal to be different in the various operating configurations for a variable displacement ICE. Accordingly, the amount of movement in the accelerator pedal required to change the amount of torque for a fully-displaced and partially-displaced engine was also different. These differences in accelerator pedal operation, to generate the same torque for different modes of operation for a previous variable displacement engine, were nuisances to the operator of the vehicle.  
           [0004]    The introduction of new engine control devices such as electronic throttle control (ETC), engine controllers, position sensors for pedal controls, and other electronics has enabled tighter control over more functions of an ICE. It is an object of the present invention to provide a variable displacement ICE whose operation is transparent to the operator of a vehicle.  
         SUMMARY OF THE INVENTION  
         [0005]    The present invention is a method and apparatus that produces a consistent relationship between engine torque and accelerator pedal position for a vehicle equipped with a variable displacement internal combustion engine (ICE). 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. An engine or powertrain controller will determine if the ICE should enter four-cylinder mode by monitoring the load and torque demands of the ICE. If the ICE is in a condition where it is inefficient to operate with the full complement of eight cylinders, the controller will deactivate the mechanisms operating the valves for the selected cylinders and also shut off fuel (and possibly spark in the case of a gasoline engine) to the cylinders. The deactivated cylinders will thus function as air springs to reduce throttling and pumping losses.  
           [0006]    As previously described, the transition between eight cylinders to four cylinders or four cylinders to eight cylinders will create changes in the air flow through the throttle plate into the ICE that also affect the torque output of the ICE and consequently the accelerator pedal position needed to generate a specific torque. The method and apparatus of the present invention uses electronic throttle control (ETC) to maintain the same engine torque and accelerator pedal position during and after a cylinder deactivation and reactivation process for the variable displacement ICE. The implementation and integration of the control schemes of the present invention will allow for a seamless transition from all cylinders firing (reactivation) to half the cylinders firing (deactivation) without disturbing the operation of the accelerator pedal.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    [0007]FIG. 1 is a diagrammatic drawing of the control system of the present invention; and  
         [0008]    [0008]FIG. 2 is a process control diagram for the control system of the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0009]    [0009]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  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 a camshaft  27  used in an overhead valve or overhead cam 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.  
         [0010]    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.  
         [0011]    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.  
         [0012]    [0012]FIG. 2 is a process control diagram for the control system  10  of the present invention. The control system  10  of the present invention is based on controlling the electronic throttle  30  to provide a consistent position or feel for the accelerator pedal  40  to generate the same torque in the ICE  12  when it is partially displaced or fully displaced. The powertrain controller  18  and electronic throttle controller  32  of the present invention include software to execute the methods of the present invention.  
         [0013]    Referring to FIG. 2, at block  50  of the process diagram, a reference torque model based on the ICE  12  displacement is used to develop a torque map or lookup table which determines the amount of torque that the driver is requesting (TDES) based on ICE  12  crankshaft  21  revolutions per minute (RPMs) and accelerator pedal  40  position. The powertrain controller  18  determines the accelerator pedal  40  position from the signal generated by the pedal position sensor  42 . The powertrain controller  18  further determines the rotations/minute (RPMs) of the ICE  12  crankshaft  21  from the pulse train generated from the crankshaft speed sensor  20 .  
         [0014]    At block  52 , the powertrain controller  18  computes a desired mass air flow or the mass-air/cylinder (MAC) needed to produce the desired torque in the ICE  12  with only half (preferably four for an eight-cylinder ICE) and all of the of the cylinders  24  activated. The term activated for a cylinder  24  will be characterized as supplying a cylinder  24  with air, fuel, and spark or any permutation thereof. The desired air mass or MAC determined at block  52  is preferably determined by using the T DES  and the ICE  12  crankshaft RPM in conjunction with a lookup table stored in the powertrain controller  18  memory. At block  54 , the powertrain controller  18  computes the nominal electronic throttle  30  position (or area) needed to produce the T DES  based in the ICE  12  with only half (preferably four for an eight-cylinder ICE) and all of the cylinders  24  activated. Generally, when running on half of the cylinders  24 , it will require a larger throttle opening for the ICE  12  to generate a given torque. The nominal electronic throttle  30  position is preferably determined by using the T DES  and the crankshaft  21  RPM feedback in conjunction with a lookup table stored in the powertrain controller  18  memory.  
         [0015]    At block  56 , the powertrain controller  18  operates a MAC servo control scheme operating in closed loop mode to insure that the requested MAC is achieved. The MAC servo control corrects or trims the nominal throttle position based on the actual measured air mass determined by the powertrain controller  18 . The measured mass air flow comprises the process variable for the MAC servo method, the setpoint is the desired mass air flow, and the MAC servo method output is the throttle position correction. The MAC servo method may comprise a control algorithm based on fuzzy logic, proportional-integral-derivative methods, and/or neural networks. The measured mass air per cylinder may utilize the actual readings of the air flow sensor  26  or a processed/conditioned mass air flow reading based on the processing of the MAP sensor  28 , the air flow sensor  26  and/or the throttle position sensor. Under nominal conditions, torque is proportional to the mass of air inducted into the ICE  12 . Accordingly, the MAC servo method ultimately determines a throttle position correction necessary to achieve the T DES . The throttle position correction component compensates for vehicle-vehicle differences, throttle wear, and other variations in the throttle flow characteristics.  
         [0016]    A summer  58  adds the throttle position correction generated at block  56  to the nominal required throttle position generated at block  54 . The final throttle position command is communicated from the powertrain controller  18  to the electronic throttle controller  32  to execute the final throttle position command for the ICE  12 .  
         [0017]    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.