Patent Publication Number: US-6655353-B1

Title: Cylinder deactivation engine control system with torque matching

Description:
FIELD OF THE INVENTION 
     The present invention relates to engine control systems for internal combustion engines, and more particularly to torque matching in a cylinder deactivation engine control system. 
     BACKGROUND OF THE INVENTION 
     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 to improve fuel economy by reducing pumping losses. Fuel economy improvement of approximately 5-10% can be realized. 
     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. 
     Conventional engine control systems that provide torque smoothing have been based on brake torque and as calibrated spark. Engine control systems using this approach does not account for changes in engine and environmental conditions. This approach also does not meet drivability specifications for maximum torque disturbances allowed during transitions between activated and deactivated modes. 
     SUMMARY OF THE INVENTION 
     An engine control system and method smoothes torque during transitions in a displacement on demand engine. A torque loss estimator generates a torque loss signal based on torque loss due to at least one of friction, pumping and accessories. A pedal torque estimator generates a desired pedal torque signal. An idle torque estimator generates a desired idle torque signal. A summing circuit generates a difference between the pedal torque signal and the idle torque and the torque loss signals and outputs a desired brake torque signal. 
     In other features, a first switch selects one of activated and deactivated modes for the torque loss estimator. A second switch selects one of activated and deactivated modes for the idle torque estimator. A position of the first and second switches is based on an operating mode of the engine. 
     In yet other features, a first summing circuit sums the desired brake torque signal and the torque loss signal for the deactivated mode. A first multiplier multiplies an output of the first summing circuit and an air per cylinder (APC) correction signal to produce a first desired deactivated indicated torque signal. A second multiplier multiplies the output of the first summing circuit and a throttle area correction signal to produce a second desired deactivated indicated torque signal. A second summing circuit sums the desired brake torque signal and the torque loss signal for the activated mode. A third multiplier multiplies an output of the second summing circuit and the APC correction signal to produce a first desired activated indicated torque signal. A fourth multiplier multiplies the output of the second summing circuit and the throttle area correction signal to produce a second desired activated indicated torque signal. 
     In still other features, a first desired APC estimator estimates a desired deactivated APC from the first deactivated desired indicated torque signal. A second desired APC estimator estimates a desired activated APC from the first desired activated indicated torque signal. A third switch communicates with the first and second desired APC estimators and selects one of the desired deactivated APC signal and the desired activated APC signal based on the operating mode of the engine. 
     In still other features, a first desired area estimator estimates a desired deactivated area from the second deactivated desired indicated torque signal. A second desired APC estimator estimates a desired deactivated area from the second activated desired indicated torque signal. A fourth switch communicates with the first and second desired area estimators and selects one of the desired deactivated area signal and the desired activated area signal based on the operating mode of the engine. 
     In still other features, the idle airflow estimator includes an idle air per cylinder estimator that generates idle airflow signals for activated and deactivated modes based on engine rpm and idle airflow. A deactivated idle torque estimator receives the deactivated idle airflow signal and generates a deactivated idle torque signal. An activated idle torque estimator receives the activated idle airflow signal and generates an activated idle torque signal. A fifth switch selects one of the activated and deactivated idle airflow signals based on an operating mode of the engine. 
    
    
     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 
     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
     FIG. 1 is a functional block diagram of an engine control system that smoothes torque during cylinder activation and deactivation according to the present invention; 
     FIG. 2 is a functional block diagram of a torque loss estimator according to the present invention; 
     FIG. 3 is a functional block diagram of a desired brake torque estimator according to the present invention; 
     FIG. 4 is a functional block diagram of a desired air per cylinder and throttle area estimator; and 
     FIG. 5 is a flowchart illustrating steps performed by the engine control system to smooth torque during activation and deactivation transitions. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     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). 
     An engine control system according to the present invention delivers a desired indicated torque, taking into account known torque losses, and matches brake torque during transitions between deactivated and activated cylinder modes. The engine control system generates a desired air per cylinder (APC Des ) and a desired throttle area (Area Des ) for both activated and deactivated operating modes. The APC Des  and Area Des  signals smooth the transition between activated and deactivated modes. While the present invention will be described in conjunction with a V8 engine that transitions to a V4 mode, skilled artisans will appreciate that the present invention applies to engines having additional or fewer cylinders such as four, six, ten and twelve cylinder engines. 
     Desired indicated torque is based on the estimates for indicated idle torque, pedal brake torque, pumping torque, engine friction torque, AC compressor torque, accessory drive torque, and torque losses from spark retard. Idle torque is computed from desired idle airflow and engine mode (for example, 8 or 4 cylinder mode). Non-idle throttle area (total area in−idle area) is used to look-up driver pedal torque requested. 
     Torque losses are the sum of engine friction losses, AC compressor losses, accessory drive losses, and pumping losses. As pumping losses change between engine modes, estimated pumping losses for the opposite mode are estimated based on vacuum transfer function tables, models or other suitable methods. The pumping loss estimate is required because the desired throttle area and air per cylinder for the opposite mode are needed before the transition occurs. 
     Torque losses from spark retards are computed for each operating mode because the same spark reduction will impact brake torque differently in each mode. Torque loss is calculated from minimum spark advance for best torque (MBT). Desired indicated torque is calculated based on the pedal, idle, V4 losses, V8 losses, and losses from spark retard. V8 losses are held during the V8−V4 throttle pre-load phase to prevent changes in desired brake torque caused by changes in the pumping losses when opening the throttle. Finally, the desired indicated torque, corrected for atmospheric conditions, is used to look up desired throttle area and air per cylinder values. 
     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 control algorithm that is executed by the controller  12  and/or the ETC  26 . One or more sensors  31  and  32  such as a pressure sensor and/or an air temperature sense pressure and/or air temperature in the intake manifold  20 . 
     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  in a transmission  60  to front and/or rear wheels. As can be appreciated by skilled artisans, the transmission can be a manual transmission or any other type of transmission. 
     Referring now to FIG. 2, a torque loss estimator  100  according to the present invention is shown. A first vacuum estimator  102  estimates vacuum in a deactivated mode (Vac_V Dest ) from measured vacuum and outputs Vac_V Dest  to a switch  106 . A second vacuum estimator  108  estimates vacuum in an activated mode (Vac_V Aest ) from measured vacuum and outputs Vac_V Aest  to a switch  110 . Measured vacuum is also input to the switches  106  and  110 . A mode signal is also input to the switches  106  and  110 . When active, the mode signal toggles the switches  106  and  110 . In other words, when the engine is in deactivated mode, the switch  106  selects the measured vacuum and the switch  110  selects Vac_V Aest . When the engine is in activated mode, the switch  106  selects Vac_V Dest  and the switch  110  selects the measured vacuum. 
     The switch  106  outputs an estimate of the vacuum for deactivated mode (D_Vac_E) to a pumping torque estimator  112 . The pumping torque estimator  112  estimates pumping torque (D_Pump_T) for the deactivated mode based upon estimated vacuum D_Vac_E and outputs D_Pump_T to a hold circuit  122 . The hold circuit  122  prevents changes in estimated pumping torques during a transition when the manifold vacuum is changing An output of the hold circuit  122  is input to a summing circuit  123 . The switch  110  outputs an estimate of the vacuum in activated mode (A_Vac 13  E) to a pumping torque estimator  116 . The pumping torque estimator  116  estimates pumping torque (A_Pump_T) for the activated mode based upon estimated vacuum A_Vac_E and outputs A_Pump_T to a hold circuit  124 . An output of the hold circuit  124  is input to a summing circuit  126 . Losses are expressed as negative torques. 
     A friction torque estimator  130  estimates friction torque (Frict_T) based upon engine rpm and oil temperature. The Frict_T, compressor torque (AC_Comp_T), and accessory drive torque (Acc_Drive_T) signals are summed by a summing circuit  134 . An output of the summing circuit is input to the summing circuits  123  and  126 . An output of the summing circuit  123  is equal to deactivated estimated torque loss (D_Loss). An output of the summing circuit  126  is equal to activated estimated torque loss (A_loss). The outputs of the summing circuits  123  and  126  are input to a switch  136  that selects one of D_Loss and A_Loss signals based upon an operating mode of the engine  16 . 
     Referring now to FIG. 3, a desired brake torque estimator  150  is shown. A pedal torque estimator  154  estimates pedal torque (Pedal_T) based upon non-idle area and engine rpm. Non_Idle_Area is the total throttle area commanded less the Idle Area portion. Non_Idle_Area is typically equal to Pedal_Area or Cruise_Control_Area. The Pedal_T signal is input to a summing circuit  156 . An air per cylinder estimator  158  estimates idle air per cylinder for activated and deactivated modes (Idle_APC_D, Idle_APC_A) based upon desired idle airflow and engine rpm. 
     Idle_APC_D is input to a first idle torque estimator  162 , which outputs a desired idle torque for deactivated mode (Tdes_ldle_D) to a switch  163 . Idle_APC_A is input to a first idle torque estimator  164 , which outputs a desired idle torque for activated mode (Tdes_Idle_A) to the switch  163 . The switch  163  selects one of Tdes_Idle_D and Tdes_Idle_A based upon the mode signal. 
     The switch  163  outputs an estimated desired idle indicated torque (Tdes_ldle) to a summing circuit  170 . The engine torque losses output by the switch  136  are also input to the summing circuit  170 . An output of the summing circuit is input to a lag filter  174 . The Pedal_T and T_idle_brake signals are input to the summing circuit  156 , which outputs a desired brake torque (T_brake_des). 
     Referring now to FIG. 4, T_brake_des is input to summing circuits  200  and  202 . The D_Losses signal is input to an inverting input of the summing circuit  202 . The summing circuit  202  generates a desired indicated deactivated torque (Ind_D_T), which is input to multipliers  206  and  208 . A_Losses are input to an inverting input of the summing circuit  200 . The summing circuit  200  generates a desired indicated activated torque (Ind_A_T), which is input to multipliers  212  and  214 . 
     An air per cylinder correction term, preferably based on charge temperature and barometric pressure, is input to the multiplier  206 . The multiplier outputs a desired deactivated indicated and corrected torque (T_DesD_lndc), which is input to a lag filter  220 . The lag filter accounts for lag in intake manifold filling after throttle area changes. As can be appreciated, the lag filter can be positioned after the APC estimator. The output of the lag filter is input to a desired air per cylinder estimator  224 , which estimates desired air per cylinder for deactivated mode (APC_DesD) from T_DesD_lndc. The APC_DesD signal is input to a switch  228 . A throttle area correction term, preferably based on charge temperature and barometric pressure, is input to the multiplier  208 . The multiplier  208  outputs a desired deactivated indicated torque (T_DesD_lndt), which is input to a desired throttle area estimator  230 . An output of the desired throttle area estimator  230  is input to the switch  232 . As can be appreciated by skilled artisans, the TdesD_lndc can be input to the desired throttle area and the throttle area can be corrected afterward. 
     An air per cylinder correction term, based on charge temperature and barometric pressure, is input to the multiplier  212 . The multiplier  212  outputs a desired activated indicated and corrected torque (T_DesA_lndc), which is input to a lag filter  240 . An output of the lag filter  240  is input to a desired air per cylinder estimator  244 , which estimates desired air per cylinder for activated mode (APC_DesA) from T_DesA_lndc. The APC_DesA signal is input to the switch  228 . A throttle area correction term, based on charge temperature and barometric pressure, is input to the multiplier  214 . The multiplier  214  outputs a desired activated indicated torque (T_DesA_lndt), which is input to a desired throttle area estimator  250 . An output of the desired throttle area estimator  250  is input to the switch  232 . 
     The switch  228  selects between APC_DesD and APC_DesA depending upon the operating mode of the engine as reflected by the V4 mode signal. The switch  228  outputs a desired air per cylinder (APC Des ). The switch  232  selects between Area_DesD and Area_DesA based upon the operating mode of the engine as reflected by the mode signal. The switch  232  outputs a desired area (Area Des ). Area Des  is preferably used by the ECT controller  26  to command the desired throttle area immediately. APC Des  is used by a proportional integral (PI) controller in software to adjust the throttle area to match APC and torque. 
     Referring now to FIG. 5, steps performed by the engine control system according to the present invention are shown generally at  300 . Control begins with step  302 . In step  304 , the controller looks up pedal torque. In step  306 , the controller determines whether the engine is operating in activated mode. If it is, control continues with step  310  and calculates pedal, idle, pump and friction torque for activated mode. Control continues with step  314  and determines whether the engine control system is transitioning from activated to deactivated mode. If it is, pumping torque for deactivated mode is calculated and pumping torque for activated mode is latched until the end of the transition in step  318 . 
     If the engine is in deactivated mode, control continues with step  324  where the controller calculates pedal, idle, pumping and friction torque for deactivated mode. In step  326 , control determines whether the engine is transitioning to activated mode. If true, control continues with step  330  and calculates pumping losses for activated mode and latches pumping losses for deactivated mode until the end of the transition. Control loops from steps  318 ,  330 ,  314  (if false) and  326  (if false) to step  332 . After steps  318  and  330 , idle brake torque, desired brake torque, corrected desired indicated torques, desired APC Des  and Area Des  are calculated in step  332 . Control loops from step  332  to  304 . 
     As can be appreciated by skilled artisans, the estimators  102 ,  108 ,  130 ,  112 ,  116 ,  154 ,  158 ,  162 ,  164 ,  224 ,  230 ,  244 , and  250  can be implemented using look up tables (LUT), models or any other suitable method or device. 
     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. 10/150,900, filed May 17, 2002, 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. 
     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.