Abstract:
An engine control system and method for a displacement on demand internal combustion engine includes a throttle preload signal generator that outputs a throttle preload area signal having a base portion and ramp out portion. A combining circuit combines the throttle preload area signal with a current throttle area signal to generate a throttle preload difference signal that adjusts throttle area to smooth transitions during at cylinder deactivation. The engine control system smoothes the transition between activated and inactivated modes by increasing throttle area and manifold pressure when transitioning between activated and deactivated modes.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to engine control systems for internal combustion engines, and more particularly to throttle preload in cylinder deactivation engine control systems.  
         BACKGROUND OF THE INVENTION  
         [0002]    Some internal combustion engines include engine control systems that deactivate cylinders under low load situations. For example, an eight cylinder can be operated using four cylinders. Cylinder deactivation improves fuel economy by reducing pumping losses.  
           [0003]    To smoothly transition between activated and deactivated modes, the internal combustion engine must produce torque with a minimum of disturbances. Otherwise, the transition will not be transparent to the driver. In other words, excess torque will cause engine surge and insufficient torque will cause engine sag, which degrades the driving experience.  
           [0004]    For example for an eight-cylinder engine, intake manifold pressure is significantly lower during eight-cylinder operation than during four-cylinder operation. During the transition from eight to four cylinders, there is a noticeable torque reduction or sagging in four-cylinder operation until the intake manifold reaches a proper manifold pressure level.  
         SUMMARY OF THE INVENTION  
         [0005]    An engine control system and method according to the present invention for a displacement on demand engine includes a throttle preload signal generator that outputs a throttle preload area signal having a base portion and ramp out portion. A combining circuit combines the throttle preload area signal with a current throttle area signal to generate a throttle preload difference signal that adjusts throttle area to smooth transitions during at least one of cylinder activation and deactivation.  
           [0006]    In other features of the invention, the throttle preload area signal further includes a ramp in portion which reduces throttle noise. A preload throttle area generator provides a preload area based on rpm and a desired air per cylinder. A preload duration generator provides a preload base duration signal based on rpm and a desired air per cylinder.  
           [0007]    In still other features, an adaptive throttle preload generator receives a measured air per cylinder and a desired air per cylinder and outputs an adjusted air per cylinder. The adjusted air per cylinder is input to an inverting input of a summing circuit. The desired air per cylinder is input to a non-inverting input of the summing circuit. The summing circuit outputs the adjusted desired air per cylinder to the preload throttle area generator and the preload duration generator.  
           [0008]    In yet other features, a ramp generator receives the preload area signal and the preload duration signal. A ramp in calibration circuit provides a ramp in period. A ramp out calibration circuit provides a ramp out period.  
           [0009]    In yet other features, an offset circuit generates an offset period. A mode actuator generates a holdoff complete signal at the offset period before an end of the preload base duration signal. Alternately, an offset circuit generates an offset period that is input to the mode actuator. A comparator generates a signal when a measured air per cylinder exceeds a desired air per cylinder. An OR circuit that is coupled to the mode actuator and the comparator generates a holdoff complete signal if the measured air per cylinder exceeds the desired air per cylinder or at the offset period before an end of the preload base duration signal. A correction circuit adjusts the preload throttle area for variations in at least one of temperature and barometric pressure.  
           [0010]    Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
         [0012]    [0012]FIG. 1 is a functional block diagram of an engine control system that preloads the throttle during cylinder activation and deactivation according to the present invention;  
         [0013]    [0013]FIG. 2 is a functional block diagram of a throttle preload signal generator according to the present invention;  
         [0014]    [0014]FIG. 3 is a functional block diagram of a modified hold off signal generator according to the present invention that can be used with the throttle preload signal generator of FIG. 2;  
         [0015]    [0015]FIG. 4 is a modified preload throttle area signal generator with correction for temperature and/or barometric pressure according to the present invention;  
         [0016]    [0016]FIG. 5 is a flowchart illustrating steps performed by the engine control system according to the present invention to generate a throttle preload signal;  
         [0017]    [0017]FIG. 6 is a flowchart illustrating steps for retarding spark;  
         [0018]    [0018]FIGS. 7 and 8 illustrate exemplary control signals for the throttle preload signal generator;  
         [0019]    [0019]FIG. 9A is a functional block diagram of a spark retard generator for cylinder deactivation;  
         [0020]    [0020]FIG. 9B is an exemplary deactivation gain waveform;  
         [0021]    [0021]FIG. 10A is a functional block diagram of a spark retard generator for cylinder activation; and  
         [0022]    [0022]FIG. 10B is an exemplary activation gain waveform.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]    The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, activated refers to operation using all of the engine cylinders and deactivated refers to operation using less than all of the cylinders of the engine (one or more cylinders not active).  
         [0024]    The engine control system according to the present invention reduces torque disturbances during cylinder deactivation by preloading the throttle (or manifold). As a result, the engine operates at an estimated air per cylinder for an activated mode (such as an 8 cylinder mode) prior to a transition to a deactivated mode (such as a 4 cylinder mode). The engine control system also increases spark retard as the throttle opens and the manifold fills. The spark retard reduces torque to maintain the same desired brake torque. As can be appreciated, the present invention has application to engines having additional or fewer cylinders such as four, six, ten and twelve cylinders.  
         [0025]    Referring now to FIG. 1, an engine control system  10  according to the present invention includes a controller  12  and an engine  16 . The engine  16  includes a plurality of cylinders  18  each with one or more intake valves and/or exhaust valves (not shown). The engine  16  further includes a fuel injection system  20  and an ignition system  24 . An electronic throttle controller (ETC)  26  adjusts a throttle area in an intake manifold  28  based upon a position of an accelerator pedal  30  and a throttle control algorithm that is executed by the controller  12 . One or more sensors  30  and  32  such as a manifold pressure sensor and/or a manifold air temperature sensor sense pressure and/or air temperature in the intake manifold  20 .  
         [0026]    A position of the accelerator pedal  30  is sensed by an accelerator pedal sensor  40 , which generates a pedal position signal that is output to the controller  12 . A position of a brake pedal  44  is sensed by a brake pedal sensor  48 , which generates a brake pedal position signal that is output to the controller  12 . Emissions system sensors  50  and other sensors  52  such as a temperature sensor, a barometric pressure sensor, and other conventional sensor and/or controller signals are used by the controller  12  to control the engine  16 . An output of the engine  16  is coupled by a torque converter clutch  58  and a transmission  60  to front and/or rear wheels.  
         [0027]    Referring now to FIG. 2, a preload signal generator  100  is shown. The preload signal generator  100  adjusts throttle area before and during the transitions between activated and deactivated modes to smooth the torque output of the engine  16 . A throttle preload area generator  104  generates a throttle area signal based on a desired airflow per cylinder in deactivated mode (APC Des ) and engine rpm. The throttle preload area generator  104  can include a lookup table (LUT), a model or any other suitable circuit that generates the throttle preload area signal. The APC Des  and engine rpm signals are also input to a preload duration generator  108 , which generates a base duration or base period for the throttle preload. The preload duration generator  108  can also include a LUT, a model, or any other suitable circuit that generates the preload duration signal.  
         [0028]    In an alternate embodiment, the APC Des  and APC Meas  signals are initially input to an adaptive throttle preload adjuster  112 , which outputs an adjustment signal. The adaptive throttle preload adjuster  112  adjusts for variation in altitude, temperature and vehicle-to-vehicle variations. The adjustment (ADJ) is input to an inverting input of a summer  116 . The APC Des  is input to a noninverting input of the summer  116 . The summer  116  outputs an adjusted desired airflow per cylinder (APC Des     —     adj ), which is input to the preload throttle area generator  104  and the preload duration generator  108 . The engine rpm signal is input to the preload throttle area generator  104  and the preload duration generator  108 .  
         [0029]    The preload area signal that is output by the preload throttle area generator  104  and the duration signal that is output by the preload duration generator  108  are input to a ramp generator  120 . Additional inputs to the ramp generator optionally include a ramp_in calibration circuit  124  and a ramp out calibration circuit  128 . The ramp in calibration circuit  124  specifies a ramp in period. Preferably, a gain applied during the ramp in period increases linearly from 0 to 1. Likewise, the ramp out calibration circuit  124  specifies a ramp out period. Preferably, a gain applied during the ramp out period decreases linearly from 1 to 0. Skilled artisans will appreciate, however, that nonlinear slopes or other waveform shapes may be employed during the ramp in and ramp out periods to improve torque smoothing and to prevent throttle noise.  
         [0030]    The ramp generator  120  generates a preload area (PL_area) signal that is output to a noninverting input of a summer  140 . A current throttle area is input to an inverting input of the summer  140 . An output of the summer  140  generates a preload difference or preload delta that is used to adjust the throttle area during cylinder deactivation transitions.  
         [0031]    The duration signal is also input to a mode actuator  144 . An offset circuit  146  generates a negative offset. The mode actuator  144  generates a hold off complete signal that is used to flag completion of a transition from activated to deactivated modes. The offset is preferably a negative offset from an end of the base duration. Alternately, the offset can be calculated from the beginning of the base duration or from other suitable signals.  
         [0032]    Referring now to FIG. 3, a modified method for flagging completion of the transition from activated to deactivated modes is shown. An output of the mode actuator  144  is input to an OR gate  150 . A comparator  154  compares APC Meas  and APC Des . If APC Meas  exceeds APC Des , the comparator  154  outputs a 1, which signals the transition from activated to deactivated modes.  
         [0033]    Referring now to FIG. 4, the preload throttle area generator  104  generates the preload area signal that is input to a multiplier  174 . A correction circuit  176  receives temperature, barometric pressure, and/or any other suitable input sensor and/or controller signals. The correction circuit  176  generates a correction signal, which is typically a signal from 0.8 to 1.5, although other scales may be used. A corrected area signal is output by the multiplier  174  to the ramp generator  120 .  
         [0034]    Referring now to FIG. 5, steps for generating throttle preload are shown at  200 . Control begins with step  202 . In step  204 , the controller  12  determines whether conditions are OK and consistent for deactivation mode. If not, control loops back to step  204 . Otherwise, if the vehicle is equipped with an automatic transmission, the controller  12  unlocks a torque converter clutch (TCC) and starts a first timer in step  208 . Allowing the torque converter to slip also helps smooth the transitions. In step  212 , the controller  12  determines whether the slip exceeds a threshold or the first timer is up. If not, control loops back to step  212 . Otherwise, control continues with step  216  and initiates throttle preload. In step  220 , control calculates throttle area and base duration. In step  224 , the total duration is calculated. The total duration is preferably equal to a sum of the ramp in period, the base period, and the ramp out period.  
         [0035]    In step  230 , the controller  12  determines whether throttle preload is in the ramp in period. If false, control continues with step  234  and sets the ramp in gain (G R     —     I ) equal to 1. Otherwise, control continues with step  238  and sets the G R     —     I  equal to (a current location in the ramp in period)/(the total ramp in period). Control continues from steps  234  and  238  with step  240 .  
         [0036]    In step  240 , the controller  12  determines whether throttle preload is in the ramp out period. If false, control continues with step  244  and sets a ramp out gain (G R     —     O ) equal to 1. Otherwise, control continues with step  248  and sets the G R     —     O  equal to (a current location in the ramp out period)/(the total ramp out period). Control continues from steps  244  and  248  with step  250 . In step  250 , the controller  12  looks up or calculates a throttle correction TC. In step  254 , control sets the throttle area equal to G R     —     I *G R     —     O *TC*A B , wherein A B  is the base area. In step  258 , control determines whether the transition is complete. If not, control loops back to step  230 . Otherwise, control ends in step  260 .  
         [0037]    Referring now to FIG. 6, steps for retarding spark are shown generally at  300 . Control enters at step  302 . In step  306 , APC Des  and APC Meas  are retrieved. A torque reduction request is calculated in step  310 . In step  314 , the controller  12  determines whether a torque reduction is required. If it is, a spark retard request is calculated in step  316  based on a torque reduction request. Control returns from steps  314  and  316 . The spark retard steps that are shown generally at  300  are preferably executed for each cylinder firing event.  
         [0038]    Referring now to FIGS. 7 and 8, exemplary control signals for an eight cylinder engine are shown. A V4 Conditions OK signal is generated to initiate a V8 to V4 transition. A V4 Conditions OK and Consistent signal is generated a first period after the V4 Conditions OK signal is generated to reduce spurious transitions and/or cycling. A Torque Converter Clutch (TCC) unlock signal is preferably triggered at the same time as the V 4  conditions OK and Consistent signal.  
         [0039]    A fixed time interval after the TCC unlock signal is generated or after the torque converter slip exceeds a target slip, an ECCC Slip OK signal is generated. A V8 to V4 Throttle Preload Start signal is generated based on the ECCC Slip OK signal. A Preload Gain signal is initiated at the same time as the V8 to V4 Throttle Preload Start signal. A typical delta throttle area transition from a steady-state V8 throttle area to a steady-state V4 throttle area is shown.  
         [0040]    An intake manifold pressure slowly increases from a V8 mode to a V4 mode. While still in V8 mode, excess torque is generated as a result of the increased manifold pressure. A spark retard signal reduces excess torque. A V4 Mode Hold Off Complete signal is based upon the offset signal subtracted from the end of the preload base duration. Alternately, the V4 Mode Hold Off Complete signal can be based upon the APC Meas  exceeding APC Des  or after a timer expires.  
         [0041]    Once the V4 Hold Off Complete signal goes high, a first deactivation device control solenoid can be turned on and a first injector can be turned off. An APC Mode To V4 signal is generated based upon an event delay from the First Injector Off signal. A V4 mode signal is based upon a event delay from the First Injector Off signal.  
         [0042]    Referring now to FIG. 9A, a spark retard generator  350  is shown. A signal selector  352  receives a APC Des  signal for a deactivated mode such as for a four cylinder APC Des4  and a desired APC signal for the activated mode such as for an eight cylinder APC Des8 . The signal selector  352  selects one of the input signals based upon a signal received from a cylinder deactivation mode circuit  354 . For example, the cylinder deactivation mode circuit  354  generates a “1” to identify the deactivated mode and a “0” to identify the activated mode. The signal selector  352  outputs the desired APC Des  to a torque reduction calculator  356  that also receives a measured APC Meas  signal. In a preferred embodiment, the torque reduction is calculated as follows:  
       I   -       (       APC   Des       APC   Meas       )     .                           
 
         [0043]    The torque reduction, which is preferably a signal between zero and one or a percentage, is input to a spark retard (RTD) calculator  360 . The RTD calculator  360  calculates a RTD from minimum best torque (MBT). The RTD calculator  360  can employ a LUT, a model with or without sensor inputs, or any other suitable method. For example, the RTD calculator  360  can calculate RTD from minimum best torque (MBT) based on APC meas  and engine rpm to  360 . The RTD from MBT is output to a final RTD calculator  364 . The final RTD calculator  364  also receives MBT and current spark advance (SA). The final RTD calculator  364  outputs a final RTD signal, which retards spark to reduce torque. A deactivation torque reduction gain circuit  366  may also be provided. In FIG. 9B, a suitable deactivation gain signal is shown. The deactivation RTD gain includes a ramp out  368  that smoothes the deactivation transition.  
         [0044]    For example, the RTD calculator  360  generates a RTD signal that is equal to −25 degrees. The final RTD calculator  364  receives an MBT that is equal to 40 degrees and a SA that is equal to 35 degrees. The final RTD calculator outputs a final spark retard of Final RTD=−(MBT+RTD)−(MBT−SA)=−(40−25)−(40−35)=−20.  
         [0045]    Referring now to FIGS. 10A and 10B, a RTD generator  370  for cylinder activation is shown. A torque reduction calculator  374  receives APC Des  and APC Meas  signals and outputs a torque reduction signal to a multiplier  376 . An activation torque reduction gain circuit  380  generates a gain signal that is also input to the multiplier  376 . An output of the multiplier  376  is input to a RTD calculator  382 , which calculates RTD from MBT. A final RTD calculator  386  receives the RTD from MBT, the MBT and the SA signals and calculates the final RTD. A cylinder reactivation mode circuit  388  generates a signal based upon deactivation mode of the engine and outputs the signal to a multiplier  390 , which also receives the final spark retard. If the reactivation mode is enabled, the cylinder reactivation mode circuit  388  outputs a “1” and the final spark retard is output. Otherwise, the cylinder reactivation mode circuit  388  outputs a “0”, which disables the final spark retard output. In FIG. 10B, a suitable activation gain signal is shown. The activation RTD gain includes a ramp out  400  that smoothes the activation transition.  
         [0046]    Airflow estimation is preferably performed using “Airflow Estimation For Engines with Displacement On Demand”, GM Ref #: GP-300994, HD&amp;P Ref #: 8540P-000029, U.S. Pat. Ser. No. ______,filed ______, which is hereby incorporated by reference. Airflow estimation systems developed by the assignee of the present invention are also disclosed in U.S. Pat. Nos. 5,270,935, 5,423,208, and 5,465,617, which are hereby incorporated by reference.  
         [0047]    Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present invention can be implemented in a variety of forms. Therefore, while this invention has been described in connection with particular examples thereof, the true scope of the invention should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification and the following claims.