Abstract:
A vehicle control system including a variable displacement internal combustion engine, a transmission coupled to the variable displacement internal combustion engine, an intake manifold coupled to the variable displacement internal combustion engine, a throttle coupled to the intake manifold, an engine controller for controlling the throttle and the variable displacement internal combustion engine, a transmission controller for controlling the transmission, and where the engine controller transfers a throttle position or load value to the transmission controller, the throttle position or load value independent of the displacement of the variable displacement internal combustion engine.

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 variable indicative of torque in a variable displacement internal combustion engine for an automatic transmission control system.  
         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 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 (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 pump air around the restriction of the throttle and from the relatively low pressure of the intake manifold through the engine and out to the atmosphere.  
           [0003]    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 cylinders as “air springs” due to the compression and decompression of the air in each deactivated cylinder.  
           [0004]    For vehicles equipped with an automatic transmission, the deactivation of cylinders for a variable displacement ICE and the corresponding changes in air flow and torque must be coordinated with the operation of the automatic transmission. Traditionally, an automatic transmission control system will receive a throttle area or a throttle position variable that is indicative of the torque output of an ICE. The throttle position or area is used by a transmission control system as an indication of how much torque the ICE produces and is used in gear selection and stabilization of transmission shifts. In a variable displacement ICE, the throttle position will change when the variable displacement ICE is in partial and full displacement to produce the same torque. Thus, with variable displacement ICEs, throttle position/area no longer represents a unique engine torque value, making throttle position/area alone an insufficient load or torque variable.  
         SUMMARY OF THE INVENTION  
         [0005]    The present invention is a method and apparatus that produces a throttle load variable for a variable displacement ICE that is independent of the displacement of the 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 driver. 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 or pumping losses.  
           [0006]    As previously described, the transition from 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. The present invention generates a throttle plate position/area signal for an automatic transmission or powertrain controller that represents the torque output of the ICE independent of the displacement of the engine. The present invention includes software having a plurality of function blocks that calculate the desired throttle position/area for varying displacements of the ICE. These function blocks will simultaneously operate and generate the throttle area/position variable, and the engine or powertrain controller will determine the correct throttle area/position command to be used, depending on the displacement of the ICE. Accordingly, a throttle position/area command will always be calculated for a fully-displaced engine and may be used as a load variable for a transmission or powertrain controller. 
       
    
    
     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  is further coupled to an automatic transmission  13  as is known in the art. 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 . An intake manifold  22  provides air to the cylinders  24  of the ICE  12 . The cylinders  24  include valves  25  that may be mechanically decoupled by a deactivation apparatus to prevent air flow through each individual cylinder  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 (ETC)  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  and a transmission controller  19  over an automotive communication network  33 . The powertrain controller  18  will transmit a throttle position/area variable to the transmission controller  19  indicative of torque to control the shifting of the automatic transmission  13 . In alternate embodiments, the electronic throttle controller  32  and transmission controller  19  may be fully integrated into the powertrain controller  18  to eliminate the need for physically separate controllers.  
         [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  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 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 simultaneously calculating a desired throttle position/area for preferably a full displacement for an eight-cylinder, variable displacement engine and a four-cylinder displacement for an eight-cylinder, variable displacement engine.  
         [0013]    Referring to FIG. 2, at block  50  of the process diagram, a reference torque model based on the full ICE  12  displacement is used to develop a torque map or lookup table which determines the amount of torque that the driver is requesting (T DES ) based on the ICE  12  crankshaft  21  rotations 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 RPMs of the ICE  12  crankshaft  21  from the pulse train generated from crankshaft speed sensor  20 .  
         [0014]    At block  52 , the powertrain controller  18  computes 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) of the cylinders  24  activated. The term activated for a cylinder  24  will be characterized as supplying a cylinder  24  with air and any permutation of fuel and spark. The MAC at block  52  is preferably determined by using the T DES  and the ICE  12  crankshaft RPM in conjunction with a mathematical model or a lookup table stored in the powertrain controller  18  memory. At block  52 , the powertrain controller  18  further computes the nominal electronic throttle  30  position/area needed to produce the TDES based on the ICE  12  with only half (preferably four for an eight-cylinder ICE) of the cylinders  24  activated. Nominal throttle position is the throttle position the engine requires (at a given ICE crankshaft RPM) to produce an engine torque of T DES . The nominal electronic throttle  30  position is preferably determined by using the T DES  and the crankshaft RPM feedback in conjunction with a mathematical model or a lookup table stored in the powertrain controller  18  memory.  
         [0015]    At block  54 , the powertrain controller  18  computes the MAC needed to produce the desired torque in the ICE  12  with all of the cylinders  24  activated. The MAC at block  54  is preferably determined by using the T DES  and the crankshaft RPM in conjunction with a mathematical model or a lookup table stored in the powertrain controller  18  memory.  
         [0016]    At block  54 , the powertrain controller  18  further computes the nominal electronic throttle  30  position/area needed to produce the T DES  based on the ICE  12  with all (preferably eight for an eight-cylinder ICE) of the cylinders  24  activated. The nominal electronic throttle  30  position is preferably determined by using the T DES  and the crankshaft RPM feedback in conjunction with a mathematical model or a lookup table stored in the powertrain controller  18  memory.  
         [0017]    Block  56  selects which pair of values to use in the control of the ETC, as blocks  52  and  54  will be running simultaneously independent of the displacement of the ICE  12 . If half the cylinders are shut off, then the output of block  52  is used, and if all the cylinders are active, then the output of block  54  is used. These outputs are sent to the ETC controller  32  for control of the position of the ETC  30 . As previously described, the ETC  30  must be varied to compensate for the displacement of the ICE  12  to generate the same amount of torque in both a partially-displaced and fully-displaced operating mode.  
         [0018]    Block  58  produces the engine torque load variable for the transmission controller  19 . The output of block  54  is always used, as block  54  produces the throttle area variable for the ICE  12  in a fully-displaced configuration. Block  58  converts the throttle area variable to throttle rotation or a load variable, using the geometry of a particular throttle body, to be communicated to the transmission controller  19 . The transmission controller  19  then adjusts the shifts of the automatic transmission  13  with reference to the throttle position load variable. Accordingly, the displacement of the ICE  12  is transparent to the transmission controller  19 , as the transmission controller  19  always receives a throttle position command representative of the torque of the ICE  12 .  
         [0019]    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.