Abstract:
An engine control system including a variable displacement internal combustion engine, a plurality of cylinders located in the internal combustion engine, a plurality of fuel injectors for providing fuel to the plurality of cylinders, a plurality of valves coupled to the plurality of cylinders, the plurality of valves controlling the air flow in and out of the cylinders, an actuation apparatus for actuating the plurality of valves, an intake manifold coupled to the internal combustion engine, a throttle coupled to the intake manifold, a controller electronically coupled to the fuel injectors, an accelerator pedal position sensor electronically coupled to the controller, and where the controller determines the number of the cylinders to provide with fuel and air and a desired engine output torque based on at least the accelerator pedal position sensor and the controller controls the throttle to control the amount of air entering the intake manifold, where the controller is capable of eliminating torque disturbances upon changes in displacement of the engine.

Description:
TECHNICAL FIELD  
         [0001]    The present invention relates to the control of internal combustion engines. More specifically, the present invention relates to methods and apparatus to provide for the control 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 variable displacement 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 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 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 throttle plate angle and 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]    Previous variable displacement ICEs suffered from driveability issues created by their control systems. A transition in a previous variable displacement eight cylinder ICE to six or four cylinder operation created noticeable torque disturbances that affected the operation of the vehicle. These torque disturbances were generally considered undesirable by consumers.  
           [0004]    The inability to control throttle position as a function of displacement in previous variable displacement ICEs contributed to the problem of torque disturbances. Previous variable displacement ICEs were equipped with conventional pedal-throttle-wire couplings that required different pedal positions for the operation of a fully displaced ICE and a partially displaced ICE. 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 also 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.  
           [0005]    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 whose operation is transparent to the operator of a vehicle.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention includes methods and apparatus that allow the operation of a vehicle with a variable displacement engine to be transparent to a vehicle operator. 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 pumping losses.  
           [0007]    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. The method and apparatus of the present invention uses ETC and control of spark advance/retard to maintain the same engine torque during the cylinder deactivation and reactivation processes for the variable displacement ICE. Correct implementation and integration of the control schemes will allow for a seamless transition from all cylinders firing (reactivation) to half the cylinders firing (deactivation) without a torque disturbance. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    [0008]FIG. 1 is a diagrammatic drawing of the control system of the present invention;  
         [0009]    [0009]FIG. 2 is a process control diagram for the control system of the present invention;  
         [0010]    [0010]FIG. 3 is a flowchart of a preferred method for determining the operation of the control system; and  
         [0011]    [0011]FIGS. 4 and 5 are timing diagrams of the cylinder activation and reactivation process. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0012]    [0012]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  may comprise a gasoline ICE or any other ICE 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  10 , the cylinders  24  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 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 pressure sensor  28  is preferably a strain gauge.  
         [0013]    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 communication network  33 . In alternate embodiments of the present invention, the electronic throttle controller  32  will be fully integrated into the powertrain controller  18  to eliminate the need for a physically separate electronic throttle controller.  
         [0014]    A brake pedal  36  in the vehicle is equipped with a brake pedal sensor  38  to determine the frequency and 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  for further processing. 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  for further processing. 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.  
         [0015]    [0015]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 position of the electronic throttle  30  and spark advance/retard to eliminate torque transients generated by the deactivation and activation of cylinders  24  in the ICE  12 . The powertrain controller  18  and electronic throttle controller  32  of the present invention include software to execute the methods of the present invention.  
         [0016]    Referring to FIG. 2, at block  50  of the process diagram, 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 per minute (RPMs) of the ICE  12  crankshaft  21  from the pulse train generated from crankshaft speed sensor  20 . The powertrain controller  18  takes the acceleration pedal  40  position and the speed of the crankshaft  21  and determines a desired ICE  12  torque (T DES ). The determination of the T DES  is preferably executed using a lookup table in the powertrain controller  18  memory. T DES  will be used as a load variable throughout the control system of the present invention. T DES  is the fundamental load variable of a torque-based engine control strategy. T DES  can be characterized as the amount of torque that the ICE  12  in a fully displaced operating mode would produce with a given throttle position and engine speed, or it may be calculated such that given an accelerator pedal  40  position the ICE  12  produces sufficient torque for a desired vehicle performance range.  
         [0017]    At block  52 , the powertrain controller  18  computes the steady-state mass-air/cylinder MAC 4  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, fuel and spark or any permutation thereof. At block  54 , the powertrain controller  18  computes the MAC 8  needed to produce the desired torque in the ICE  12  with all of the cylinders  24  activated. The MAC at blocks  52  and  54  is preferably determined by using the T DES  and the crankshaft  21  RPM in conjunction with a lookup table stored in the powertrain controller  18  memory.  
         [0018]    At block  56 , a model of the intake manifold  22  filling dynamics with only half the cylinders  24  activated is constructed. The model functions as a unity gain filter. The purpose of  56  is to produce the correct MAC trajectory as a function of time. At block  58 , a model of the intake manifold  22  filling dynamics with all of the cylinders  24  activated is constructed. The output of block  56  is the MAC trajectory desired for half the cylinders  24  enabled (MAC 4DES ), and the output of block  58  is the MAC desired for all of the cylinders  24  enabled (MAC 8DES ). A discrete software switch  60  will determine whether the MAC desired for partial or full displacement of the ICE  12  is forwarded to block  61 . The state of the software switch  60  is determined by the displacement of the ICE  12  and a cylinder deactivation flag CD_flag — 1 (operation of CD_flag — 1 will be described below in the specification). Accordingly, when the ICE  12  is operating with only half the cylinders  24 , the MAC 4DES  from block  56  will be transferred to block  61  as MAC DES , and when the ICE  12  is operating with all the cylinders  24 , the MAC 8DES  from block  58  will be transferred to block  61  as MAC DES .  
         [0019]    At block  61 , the powertrain controller  18  will use a set of dynamic models of the electronic throttle  30  to further process the MAC DES  desired from blocks  56  and  58  into a dynamic MAC desired (MAC*). The MAC* differs from the MAC DES  by the additional dynamics associated with the physical movement of the throttle.  
         [0020]    At the summing junction  62 , the MAC measured (MAC m ) and the MAC* are processed to produce an MAC error. The MAC error at block  64  is input to a control algorithm in the powertrain controller  18  to produce a desired electronic throttle  30  output control signal (Throttle*). The control algorithm includes, but is not limited to, a proportional-integral control algorithm, a proportional-integral-derivative control algorithm, a fuzzy logic algorithm, a control algorithm utilizing neural networks, and/or any control-theory based algorithm. The desired electronic throttle output control signal determines the speed and positioning of the electronic throttle  30 . The output control signal is communicated from the powertrain controller  18  to the electronic throttle controller  32 , via a serial link, or in alternate embodiments an analog signal. A feedforward factor (Throt DES ) is added to the electronic throttle output control signal at summing junction  66 . The Throt DES  value is compensated at block  73  to provide for desired air dynamics for displacement changes. The feedforward factor will drive the throttle plate  30  to the position required to deliver MAC* to the cylinders and thus the desired MAC will be reached more quickly.  
         [0021]    The feedforward factor added at summing junction  66  is generated by the following control method. At block  68 , the powertrain controller  18  computes the electronic throttle  30  position (or area) Throt 4  needed to produce the T DES  based in the ICE  12  with only half (preferably four for an eight-cylinder ICE) of the cylinders  24  activated. At block  70 , the powertrain controller  18  computes the electronic throttle  30  position Throt 8  needed to produce the T DES  in the ICE  12  with all of the cylinders  24  activated. The desired throttle position at blocks  68  and  70  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. A discrete software switch  72  will determine whether the electronic throttle  30  position desired for partial or full displacement of the ICE  12  is forwarded to summing junction  66 . The state of the software switch is determined by the displacement of the ICE  12  and the cylinder deactivation flag CD_flag — 1. Accordingly, when the ICE  12  is operating with only half the cylinders  24 , the desired electronic throttle  30  position Throt 4  generated at block  68  will be transferred to summing junction  66 , and when the ICE  12  is operating with all the cylinders  24 , the desired electronic throttle  30  position Throt 8  generated at block  70  will be transferred to summing junction  66 .  
         [0022]    The MAC* output from block  61  will be transferred to the spark control advance/retard portion of the control system of the present invention to smooth the activation and deactivation of cylinders  24  in the ICE  12 . At block  74 , the powertrain controller  18  computes the torque of the ICE  12  with only half (preferably four for an eight-cylinder ICE) of the cylinders  24  activated using the MAC* output from block  61  and crankshaft RPM in conjunction with a lookup table in the powertrain controller  18  memory. At block  76 , the powertrain controller  18  computes the torque of the ICE  12  with all of the cylinders  24  activated using the MAC* output from block  61  and crankshaft RPM in conjunction with a lookup table in the powertrain controller  18  memory.  
         [0023]    At block  78 , a model of the torque dynamics as a function of cylinder  24  air and engine speed with only half the cylinders  24  activated is constructed. The model of block  78  functions as a dynamic filter, since there can be a slight lag in torque production even for an instantaneous change in MAC*, due, for example, to transient fueling dynamics. At block  80 , a model of torque dynamics as a function of the cylinder air and engine speed with all of the cylinders  24  activated is constructed. The model of block  80  also functions as a dynamic filter, since there can be a slight lag in torque production even for an instantaneous change in MAC*. A discrete software switch  82  will determine whether the torque expected for partial or full displacement of the ICE  12  is forwarded to block  84 . The state of the software switch is determined by the displacement of the ICE  12  and a cylinder deactivation flag CD_flag — 2. Accordingly, when the ICE  12  is operating with only half the cylinders  24  activated, the expected torque generated at block  78  will be transferred to block  84 , and when the ICE  12  is operating with all the cylinders  24 , the expected torque generated at block  80  will be transferred to block  84 .  
         [0024]    At block  84 , the powertrain controller executes an intake to torque delay algorithm that accounts for the time it takes between when the mass of air (MAC) is computed and when the power stroke (at which the torque is produced) occurs. The delayed expected output torque from block  84  is input to summing junction  86  along with the T DES  generated at block  50  to generate the desired change in torque required from a change in spark advance/retard δT SA . The δT SA  is processed at block  88  by the powertrain controller  18  in conjunction with crankshaft  21  RPMs and the MAC m  to generate a spark advance/retard command δ SA .  
         [0025]    [0025]FIG. 3 includes flowcharts of the reactivation and deactivation requests from the powertrain controller to set the flags CD_flag — 1 and CD_flag — 2 previously referenced in FIG. 2. When it is necessary to reactivate the deactivated cylinders, the subroutine characterized by blocks  100  through  104  is called. At block  100 , the powertrain controller  18  generates a reactivation request and sets CD_flag — 2=CD_flag — 1=0 at block  102 . For a reactivation request, both flags are set to zero at the same time, by block  102 . Next, the powertrain controller  18  returns to  115  to run the control process represented by the block diagram in FIG. 2. At block  116 , the powertrain controller returns to normal processing. Accordingly, when the control process represented by the block diagram in FIG. 2 is run, both CD_flag — 1 and CD_flag — 2 will be equal to zero until a deactivation process occurs.  
         [0026]    When the powertrain controller  18  determines that it can deactivate one-half of the cylinders  24 , it generates a deactivation request and calls the subroutine initiated by block  106 . At block  108 , CD_flag — 1 is set to 1 to indicate the ICE  12  is ready to operate with only half the cylinders  24  activated. Block  110  determines if the T AIR     —     4  (t−Δt) generated at block  78  is greater than or equal to T DES . If T AIR     —     4  (t−Δt)&lt;T DES , then the electronic throttle  30  has not had enough time to move to a partial displacement position and the ICE  12  would not be able to produce sufficient torque with respect to T DES . (For reference, an increased electronic throttle  30  position indicates greater air flow and a decreased electronic throttle  30  position indicates lesser air flow.) In this case, block  115  is executed to run the control process represented by the block diagram in FIG. 2, and then the powertrain controller  18  returns to normal processing at block  116 . Accordingly, when the control process represented by the block diagram in FIG. 2 is executed, CD_flag — 1=1 and CD_flag — 2=0, so that the powertrain controller  18  will increase the electronic throttle  30  position and hence the MAC*. The flag CD_flag — 2 will be set=0, and switch  82  will pass T AIR     —     8  as T AIR  which is greater than T DES , and blocks  84 - 88  will retard the spark advance, thus negating the extra torque produced by the increased electronic throttle  30  position. If at 110 T AIR     —     4  (t−Δt)&gt;=T DES , the electronic throttle  30  has moved far enough to generate the T DES , then set CD_flag — 2=1 and execute block  112  with CD_flag — 1=1 and CD_flag — 2=1. In this case, the output of block  84  [T AIR (t−Δt)] will be equal to or greater than T DES  and blocks  86 - 88  will generate a zero value for SA. The net result is that when the torque production of the ICE  12  drops due to running on half the cylinders  24 , there is an immediate compensating torque increase by removing spark retard.  
         [0027]    [0027]FIG. 4 is a timing diagram generally illustrating the interaction between the plots for the signals CD_flag — 1  117  (input to the blocks  60  and  72 ), MAC DES    118 , MAC*  128 , T DES    120 , T AIR    122 , and δTSA  124  for signal timing during reactivation of the cylinders  24  for the ICE  12 . As can be seen in FIG. 4, CD_flag — 1 on the plot  116  indicates a transition for the ICE  12  from four-cylinder to eight-cylinder operation. In response to the reactivation of cylinders, the MAC DES  changes instantaneously to a smaller value. Due to the throttle dynamics generated at block  61  and the manifold dynamics generated at block  58 , the value of MAC DES  will decrease along the slope of the plot  128  as MAC*. The MAC DES  will decrease because the displacement of the ICE  12  has increased and the MAC needed to generate the same T DES  in a four-cylinder ICE is greater than that of an eight-cylinder ICE. As can be seen by plot  120 , T DES  is held constant. The signal T AIR  output of block  82  represents the torque generated by the MAC, assuming nominal spark advance and a stoichiometric air-fuel ratio. FIG. 4 illustrates that after a period of time Δt  126 , T AIR  suddenly increases. This is because initially MAC* is greater than MAC DES  (which is the value needed for T AIR  to equal T DES ), and after the initial increase, T AIR  decreases as MAC* decreases. In order to avoid the disturbance in T AIR  from being felt by the driver, it is necessary to produce an equal and opposite torque disturbance. This is the signal represented by the plot  124  δT SA  and is produced by retarding the spark advance as determined in block  88 .  
         [0028]    [0028]FIG. 5 is a signal timing diagram during deactivation of cylinders  24  for the ICE  12 . As can be seen in FIG. 5, CD_flag — 1 on plot  140  indicates a transition from eight-cylinder to four-cylinder operation. A plot  144  of MAC* is shown as increasing due to the need for more MAC to generate the same T DES  (as shown by plot  146 ) in four-cylinder operation versus eight-cylinder operation. However, if MAC* is increased while the ICE  12  is still operating on eight cylinders, the torque would increase as shown in T AIR  plot  148 . To counter this unwanted increase in torque, δT SA  is decreased as shown in plot  150 . Once MAC* has reached its desired new value, as shown in the plot  144 , the signal CD_flag — 2 illustrated in plot  142  is raised, indicating that the ICE  12  is ready to begin operating on four cylinders. After the intake-to-torque delay At  152 , the torque T AIR  falls as shown in the plot  148 , and the torque δT SA  mirrors T AIR  as shown in the plot  150 . Since the observed torque is a sum of T AIR  and δT SA , it remains constant throughout the deactivation.  
         [0029]    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.