Abstract:
A method and system for controlling fuel mass during transient engine conditions is based on an open loop transient fuel compensation algorithm so as to provide transient fuel compensations that address drivability requirements associated with the acceleration mode and deceleration mode of engine operation as well as the ease of the calibration during engine cranking mode.

Description:
BACKGROUND OF INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates to methods and systems for controlling an amount of fuel delivered to an individual engine cylinder during transient engine operating conditions.  
           [0003]    2. Background Information  
           [0004]    Under a steady-state operating condition of an internal combustion engine, the mass of the air charge for each cylinder event is constant. The fuel transport mechanisms in the fuel intake have reached near equilibrium conditions, allowing a constant mass of injected fuel for each combustion event in each cylinder. However, when the engine operating condition is not steady-state, such as in an acceleration mode or deceleration mode, the mass of injected fuel required to achieve the desired air/fuel ratio in each cylinder is not constant as a result of transients in the mass of air charge being delivered to the cylinders.  
           [0005]    Various attempts have been made to improve control of air/fuel ratios during transient engine conditions. For example, U.S. Pat. No. 5,746,183 describes control of fuel mass based on a fuel puddle model representative of a fuel puddle that theoretically is present in the intake manifold. The fuel puddle model uses a first order X and tau coupled inverse compensator model of the fuel puddle to control transient fuel compensation. For example, an initial estimate of desired fuel mass of the puddle per cylinder embodies a fuel/air function (f_a_ratio[n]) that represents a desired in-cylinder fuel-air ratio for that cylinder&#39;s bank and comprises a closed loop input to the inverse compensator mathematics from another section of the engine control routine.  
           [0006]    The dynamic response of the inverse compensator model is limited by the model and mathematical constraints imposed by the model (e.g. the coupling between X and tau as well as use of single X and tau values for both acceleration and deceleration modes) and as a result may encounter difficulty in responding to different drivability requirements associated with acceleration and deceleration modes of engine operation. The model-based control system is designed to provide mandatory fuel compensation during the engine crank mode. The mandatory fuel compensation during engine crank mode has resulted in increased calibration efforts to make this system responsive, primarily due to the interaction between transient compensation and crank fuel calculation.  
         SUMMARY OF INVENTION  
         [0007]    The present invention provides a method and system for controlling fuel mass during transient engine conditions that is based on a transient fuel compensation algorithm that provides transient fuel compensations that address drivability requirements associated with the acceleration mode and deceleration mode of engine operation as well as the cranking mode of engine operation.  
           [0008]    In accordance with an illustrative embodiment of the invention, a method and system for determining fuel mass to be delivered to each cylinder of an internal combustion engine during transient engine operation involve determining a desired in-cylinder fuel mass for combustion based on a plurality of engine parameters, determining whether a current mode of engine operation is an acceleration mode or a deceleration mode, and determining a transient fuel mass compensation factor (mf_tfc [inj]) in response to the determined current acceleration or deceleration mode of engine operation. The transient fuel mass compensation factor and a base desired in-cylinder fuel mass (calculated from fuel air ratio) are combined to provide a desired injected fuel mass for the next combustion event for each cylinder.  
           [0009]    In a particular embodiment of the invention, the desired in-cylinder fuel mass for combustion is determined from engine parameters representing air charge, feedforward air-fuel demand, and air/fuel stoichiometric ratio.  
           [0010]    In another particular embodiment of the invention, the determination of the current mode of engine operation is made by comparing the desired in-cylinder fuel mass for combustion and a filtered desired in-cylinder fuel mass obtained using the prior injection history of each cylinder and a time constant determined in response to the determined current acceleration or deceleration mode of engine operation.  
           [0011]    In still another particular embodiment of the invention, the determination of a transient fuel mass compensation factor is made by obtaining a difference between the desired in-cylinder fuel mass for combustion and the filtered desired in-cylinder fuel mass and multiplying the difference by a value of a gain multiplier determined in response to the determined current acceleration or deceleration mode of engine operation.  
           [0012]    In still another particular embodiment of the invention, the method and system of the invention optionally can force the transient fuel compensation factor to zero during an engine crank mode such that no fuel transient compensation is conducted during the engine crank mode.  
           [0013]    The present invention is advantageous for determining transient fuel compensations for each cylinder independently for the acceleration mode or deceleration mode of engine operation to improve drivability and avoids transient fuel compensation during the engine crank mode, reducing calibration requirements for the method and system.  
           [0014]    The above advantages of the present invention will become more readily apparent from the following description taken with the following drawings. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0015]    [0015]FIG. 1 is a schematic view of an internal combustion engine and an electronic engine control unit for practicing an embodiment of the invention.  
         [0016]    [0016]FIG. 2 is flow diagram illustrating the general sequence of steps associated with the operation of an illustrative embodiment of the invention. 
     
    
     DETAILED DESCRIPTION  
       [0017]    Referring to FIG. 1, the present invention can be practiced in connection with an internal combustion engine  10  that includes a plurality of combustion chambers or cylinders  52 , one of which is shown in FIG. 1. The engine  10  is controlled by an electronic control unit (ECU)  12  having a read only memory (ROM)  11 , a central processing unit (CPU)  13 , a random access memory (RAM)  15 , and a keep alive (KAM) memory  19 , which retains information when the engine ignition key is turned-off for use when the engine is restarted. The ECU  12  can be embodied by an electronically programmable microprocessor, a microcontroller, an application-specific integrated circuit, or a like device to provide a predetermined control logic.  
         [0018]    The ECU  12  receives a plurality of signals from the engine  10  via an input/output port  17 . Such signals include, but are not limited to, an engine coolant temperature (ECT) signal  14  from an engine coolant temperature sensor  16  which is exposed to engine coolant circulating through the coolant passage  18 , a cylinder identification number (CID) signal from a CID sensor  22 , a throttle position signal  24  generated by a throttle position sensor  26 , a signal  28  which may be a profile ignition pick-up (PIP) signal generated by a crank position sensor  30 , a heated exhaust gas oxygen (HEGO) signal  32  from HEGO sensor  34 , an air intake temperature signal  36  from an air temperature sensor  38 , and an air flow signal  40  for an air flow sensor  42 .  
         [0019]    The ECU  12  processes these signals received from the engine sensors and generates corresponding signals, such as a fuel injector pulse waveform signal that is transmitted to each fuel injector  44  of each cylinder  52  on a signal line  46  to control the amount of fuel delivered by each fuel injector  44 . ECU  12  also generates an ignition signal (not shown) for receipt by a spark plug (not shown) associated with cylinder  52  in known manner to initiate combustion of the air and fuel mixture in cylinder  52 . An intake valve  48  associated with each combustion chamber or cylinder  52  operates to open and close intake port  50  to control the entry of an air/fuel mixture into each combustion chamber or cylinder  52 . Although the embodiment of the invention is illustrated in connection with what is typically referred to as a port injected engine, the present invention is not so limited and also applies to a direct injection engine in which the fuel is injected directly into the combustion chamber of the engine  10 .  
         [0020]    The air flow signal  40  (from which an air charge estimate is computed) from air flow sensor  42  is updated every profile ignition pickup (PIP) event for each cylinder  52 , which is used to trigger all fuel calculations. The average desired fuel-air ratio is used in calculation of the desired in-cylinder fuel mass for combustion in each cylinder  52 . This desired in-cylinder fuel mass for combustion is then used as the basis for all fuel calculations for each cylinder including initial main pulse scheduling, and injector updates. Since the initial main fuel for each cylinder must be scheduled in advance of delivery, the air charge estimate can change radically during transient engine operating conditions, such as acceleration mode and deceleration mode of engine operation.  
         [0021]    The present invention provides a method and system for controlling fuel mass during such transient engine operating conditions to each cylinder of multi-cylinder internal combustion engine, the method and control system being based on a transient fuel compensation algorithm that controls transient fuel compensations independently for the acceleration mode and the deceleration mode of engine operation and in response to a plurality of engine parameters.  
         [0022]    Referring to FIG. 2, there is shown a flow diagram illustrating a routine performed by control logic of the ECU  12 . The parallel steps shown in FIG. 2 can be implemented using interrupt-driven programming strategies, object-oriented programming, or the like. The steps shown in FIG. 2 typically comprise a portion of a larger routine which performs other engine control functions.  
         [0023]    Pursuant to an illustrative embodiment of the invention, the routine performs a so-called PIP task, Boundary Angle task, and Background task. The PIP task is an event based foreground (high priority) task which occurs every two (2) revolutions for each cylinder. The air charge value is updated during that event. The Boundary Angle task is conducted at the boundary angle interrupt for each cylinder, which takes place at the crank angle position where no more fuel can be ingested for the current combustion cycle. For purposes of illustration and not limitation, the boundary angle interrupt occurs when the intake valve  48  is closing to two-thirds of its full open position and occurs every two revolutions for each cylinder.  
         [0024]    The Background task of step  100  is conducted periodically on a fixed time basis, as opposed to an event basis, such as for example every 50 milliseconds to generate a value of a time constant TC and a value of a gain pursuant to the invention. In particular, the Background task calculates a value of a time constant TC and a value of a gain for the acceleration mode and a value for a time constant TC and a value of a gain for the deceleration mode of engine operation using three dimensional tables and/or two dimensional functions collectively designated F x  and obtained by direct measurement and/or inference. One set of such tables and/or functions is provided for the acceleration mode and another set is provided for the deceleration mode. The Background task calculations thereby provide two independent sets of TC and gain values, one set for the acceleration mode and the other set for the deceleration mode independently of one another.  
         [0025]    The gain and TC values are calculated based on engine operating conditions that include manifold pressure, coolant temperature, speed, time since start, intake valve temperature, fuel content (% methanol), fuel volatility, fuel temperature, injector cutoff request, variable valve timing control request, etc.  
         [0026]    For purposes of illustration and not limitation, the following can be calculated:  
         [0027]    acceleration gain and TC:  
         [0028]    tfc_gn_a=F 1  (coolant temperature, time since start)+ 
         [0029]    F 2 (manifold pressure, engine speed)+ 
         [0030]    F 3 (fuel composition)+F 4 (valve timing)+ 
         [0031]    F 5 (fuel volatility)  
         [0032]    tfc_tc_a=F 6 (coolant temperature, time since start)+ 
         [0033]    F 7 (manifold pressure, engine speed)+ 
         [0034]    F 8 (fuel composition)+F 9 (valve timing)+ 
         [0035]    F 10 (fuel volatility)  
         [0036]    deceleration gain and TC:  
         [0037]    tfc_gn_d=F 11 (coolant temperature, time since start)+ 
         [0038]    F 12 (manifold pressure, engine speed)+ 
         [0039]    F 13 (fuel composition)+F 14 (valve timing)+ 
         [0040]    F 15 (fuel volatility)  
         [0041]    tfc_tc_d=F 6 (coolant temperature, time since start)+ 
         [0042]    F 17 (manifold pressure, engine speed)+ 
         [0043]    F 18 (fuel composition)+F 19 (valve timing)+ 
         [0044]    F 20 (fuel volatility)  
         [0045]    In the Background task, the filtered in-cylinder fuel mass, mf_des [inj], can be forced in an embodiment of the invention to the value of instantaneous desired incylinder fuel mass for combustion (tfc_mf_des) throughout the crank mode, reflecting that the transient fuel compensation has been disabled for the duration. Also in the same task, the filtered in-cylinder fuel mass, mf_des [inj], can be compensated for an IMRC (intake manifold runner control) transition in a manner described in U.S. Pat. No. 6,257,206, the teachings of which are incorporated herein by reference.  
         [0046]    The logic control for transient fuel compensation begins with step  200  wherein an instantaneous desired in-cylinder fuel mass for combustion (tfc_mf_des) is calculated for each combustion event:  
         [0047]    (1) tfc_mf_des=cyl_air_chg_/(spk_lambse*ful_stoic_af)_pcomp_lbm  
         [0048]    where cyl_air_chg_ is the current estimate of inducted air mass per cylinder determined from air flow signal  40 ,  
         [0049]    spk_lambse is the average desired fuel-air ratio determined  
         [0050]    by feedforward control strategy (e.g. open loop fuel control),  
         [0051]    ful_stoic_af is the stoichiometric air-fuel ratio, and  
         [0052]    pcomp_lbm is the estimated fuel mass that the cylinder receives from a conventional purge system (not shown).  
         [0053]    The desired in-cylinder fuel mass is neither cylinder bank specific nor cylinder specific, meaning that the same value thereof is used for calculating a particular transient fuel compensation for each cylinder. Although the invention is not so limited, for the particular application described, the desired in-cylinder fuel mass for combustion (tfc_mf_des) is determined without the influence of closed loop limit cycles. For example, equation (1) uses the listed plurality of engine parameters, all of which are available from open loop control algorithm.  
         [0054]    The logic control flows to step  202  where there is a determination of whether the current transient mode of engine operation is an acceleration mode or a deceleration mode. This determination is made for each cylinder by determining the difference between the instantaneous desired in-cylinder fuel mass for combustion (tfc_mf_des) and a filtered version of that fuel mass for each fuel injector as follows:  
         [0055]    (2) delta_mass_[inj]=tfc_mf_des−mf_des[inj] 
         [0056]    where mf_des[inj] is the filtered desired in-cylinder fuel  
         [0057]    mass for each cylinder determined as described below by equation (3).  
         [0058]    If the delta_mass[inj] value for a particular fuel injector is greater than or equal to 0, then an acceleration mode of engine operation is determined, and a flag, tfc_acc_flg[inj], is set in control logic indicating a determined current acceleration mode. Otherwise, a deceleration mode of engine operation is determined, and flag, tfc_acc_flg[inj], is cleared in control logic, indicating a determined current deceleration mode.  
         [0059]    The filtered desired in-cylinder fuel mass for each fuel injector, mf_des[inj], is determined by Boundary Angle task using equation (3) for each cylinder that has just crossed its boundary angle as follows:  
         [0060]    (3) mf_des[inj]=mf_des k−1 [inj]*TC/(1+TC)+tfc_mf_des/(1+TC)  
         [0061]    where mf_des k−1 [inj] is the last pass value of the same parameter and TC (or tc) is a time constant value determined in the Background task and pursuant to the invention will be either a value, tfc_tc_a, for a determined current acceleration mode or a value, tfc_tc_d, for a determined current deceleration mode of engine operation depending on the status flag tfc_acc_flg[inj] set in step  102 . That is, if tfc_acc_flg[inj]=accel, then the TC value, tfc_tc_a, is determined. If tfc_acc_flg[inj]=decel, then the TC value, tfc_tc_d_, is determined.  
         [0062]    When a cylinder is cut out of operation, the tfc_mf_des will be substituted by zero in equation (3) to reflect the deactivation of the fuel injector associated with that cut-out cylinder.  
         [0063]    The values of mf_des_[inj] are updated in bookkeeping step  300  for use in the next Boundary Angle task.  
         [0064]    The logic control flows to step  204  where a transient in-cylinder fuel mass compensation (mf_tfc_[inj]) is calculated for each fuel injector as follows:  
         [0065]    (4) mf_tfc_[inj]=delta_mass_[inj]*gain  
         [0066]    where the gain value is determined in the Background task and pursuant to the invention will be either a value, tfc_gn_a, for a determined current acceleration mode or a value, tfc_gn_d, for a determined current deceleration mode of engine operation as determined by the status flag tfc_acc_flg[inj] set in step  202 . That is, if tfc_acc_flg [inj]=accel, then the gain value, tfc_gn_a, is determined. If tfc_acc_flg[inj]=decel, then the gain value, tfc_gn_d_, is determined.  
         [0067]    The transient in-cylinder fuel mass compensation (mf_tfc_[inj]) can comprise a transient adder for a determined current acceleration mode of engine operation or a transient subtractor for a determined current deceleration mode of engine operation. The transient in-cylinder fuel mass is determined independently for the acceleration mode and for the deceleration mode pursuant to the invention as is apparent from the above description.  
         [0068]    In step  206 , the transient in-cylinder fuel mass compensation (mf_tfc_[inj]) is combined with a base desired fuel mass (calculated from fuel air ratio) to provide an injected fuel mass for each cylinder for the next combustion event. The base desired in-cylinder fuel mass is calculated as described in U.S. Pat. No. 5,746,183, the teachings of which are incorporated herein by reference, and, in particular, is calculated as set forth in equation (4) of the patent during the PIP task.  
         [0069]    During a crank mode of operation, the logic control can force the value of delta_mass to zero (i.e. mf_des[inj]=tfc_mf_des) to ensure that there is no transient fuel compensation during the crank mode of engine operation. That is, transient fuel compensation can be decoupled from the crank mode of engine operation in practice of an embodiment of the invention. The invention is not so limited as transient fuel compensation optionally can be conducted during the crank mode.  
         [0070]    The above steps  202 ,  204  and  206  are performed for all of the fuel injectors  44  so as to control fuel mass delivered to all cylinders under transient engine conditions.  
         [0071]    While the invention has been described in terms of specific embodiments thereof, it is not intended to be limited thereto but rather only as set forth in the appended claims.