Abstract:
A control system for controlling an engine ( 10 ) of an automotive vehicle has an air charge sensor ( 47 ) generating a first signal indicative of an air charge, a purge flow valve ( 74 ) generating a second signal indicative of purge flow. A controller ( 42 ) is coupled to the air charge sensor and the purge flow valve. The controller ( 42 ) is configured to determine a first amount of fuel to deliver to the cylinder based on the first signal and a desired air-fuel ratio. The controller is configured to calculate a first air-fuel ratio change value based on the first signal and is configured to calculate a second air-fuel ratio change value based on the second signal. The controller is configured to deliver a second amount of fuel to the cylinder based on the first amount of fuel and the first and second air-fuel ratio change values.

Description:
BACKGROUND OF INVENTION 
     The present invention relates generally to a control system for controlling the air fuel ratio of an internal combustion of an automotive vehicle, and more particularly, to a method and apparatus for controlling a fuel pulse width in response to changes in a normalized air charge and in a normalized purge vapor flow from an engine fueling system. 
     Minimizing tailpipe emission is an objective of closed loop fuel systems. Closed loop fuel systems include a catalytic converter that is used to treat the exhaust gas of an engine. The efficiency of a catalytic converter is affected by the ratio of air to fuel supplied to the engine. At the stoichiometric ratio, catalytic conversion efficiency is high for both oxidation and reduction conversions. The air/fuel stoichiometric ratio is defined as the ratio of air to fuel which in perfect combustion would yield complete consumption of the fuel. The air/fuel ratio Lambda of an air/fuel mixture is the ratio of the amount by weight of air divided by the amount by weight of fuel to the air/fuel stoichiometric ratio. Closed loop fuel control systems are known for use in keeping the air/fuel ratio in a narrow range about the stoichiometric ratio, known as a conversion window. 
     The difficulty with known systems is that the catalyst is very sensitive to errors in the input air fuel mixture. Fueling errors may result in catalyst breakthrough and therefore a reduction in the efficiency of the catalyst. 
     Known engine air-fuel control systems generally execute control steps using several stored conversion/determination tables to control delivery of an air-fuel mixture to an engine cylinder. For example, known systems generally perform the following steps: (i)measure a signal generated by an mass air-flow sensor; (ii)determine a measured air flow value using an air flow table indexed by a voltage of the mass air flow sensor signal; (iii)determine an air charge per cylinder using an air charge table indexed by the measured air flow and the speed (RPM) of the engine; (iv)determine a fuel charge based on fuel table indexed by air charge per cylinder; (v)calculate a fuel injector pulse width based on the fuel charge. 
     As discussed, the known engine control systems utilize the air flow table, the air charge table, and the fuel table for engine air-fuel control. The development of these tables during engine calibration at a vehicle design center involves considerable time and effort. Further, the numerous tables require a relatively large amount of memory in the engine controllers which leads to increased engine cost. 
     SUMMARY OF INVENTION 
     The present invention provides a method and apparatus for controlling the operation of an engine of the automotive vehicle by determining an overall fuel pulse width that is a function of air charge load and the purge function. 
     In one aspect of the invention, a method for controlling an amount of fuel delivered to a cylinder of an internal combustion engine includes determining a first amount of fuel to deliver to said cylinder based on a current air charge of said cylinder and a desired air-fuel ratio, calculating a first air-fuel ratio change value based on an amount of change in the air charge, calculating a second air-fuel ratio change value based on an amount of change in purge flow to the cylinder, and delivering a second amount of fuel to the cylinder based on the first amount of fuel, and the first and second air-fuel ratio change values. 
     In a further aspect of the invention, a control system for controlling an engine of an automotive vehicle has an air charge sensor generating a first signal indicative of an air charge, a purge flow valve generating a second signal indicative of purge flow. A controller is coupled to the air charge sensor and the purge flow valve. The controller is configured to determine a first amount of fuel to deliver to the cylinder based on the first signal and a desired air-fuel ratio. The controller is configured to calculate a first air-fuel ratio change value based on the first signal and is configured to calculate a second air-fuel ratio change value based on the second signal. The controller is configured to deliver a second amount of fuel to the cylinder based on the first amount of fuel and the first and second air-fuel ratio change values. 
     The inventors herein have recognized that engine air-fuel control systems can be greatly simplified by (i) determining an initial fueling amount upon engine startup and (ii) adjusting the fueling amount based on “changes” in engine load and vapor purge. By simply adjusting the fuel amount based on subsequent changes in engine load and vapor purge, the inventive control strategy eliminates the air charge table and the fuel table, required by known systems. Thus, the inventive control system results in considerable timing savings during vehicle calibration (since the air charge table and the fuel table need not be developed) for a given engine. Further, by eliminating the two tables, the memory size of the engine controller can be reduced resulting in engine cost savings. Further, one skilled in the art will recognize that the method is much simpler to implement than known methods. 
    
    
     Other advantages and features of the present invention will become apparent when viewed in light of the detailed description of the preferred embodiment when taken in conjunction with the attached drawings and appended claims. 
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a block diagrammatic view of an engine having a control system according to the present invention. 
     FIG. 2A is a plot of a Δ load/load versus λ a . 
     FIG. 2B is a plot of fuel multiplier versus a (λ f ). 
     FIG. 2C is a plot of purge volume/air mass versus (λ p ). 
     FIG. 3 is a block diagrammatic view of a control system according to the present invention. 
     FIG. 4 is a block diagrammatic view of adaptation monitor logic according to the present invention. 
     FIG. 5 is a flow chart of adaptation monitor logic according to the present invention. 
     FIG. 6 is a plot illustrating a recursive method for adjusting the models show in FIG.  2 A. 
    
    
     DETAILED DESCRIPTION 
     In the following example the same reference numerals and signal names will be used to identify the respective same components and the same electrical signals in the various views. 
     Referring now to FIG. 1, internal combustion engine  10  is controlled by electronic controller  12 . Engine  10  has a plurality of cylinders  14 , one of which is shown. Each cylinder has a cylinder wall  16  and a piston  18  positioned therein and connected to a crankshaft  20 . A combustion chamber  22  is defined between piston  18  and cylinder wall  16 . Combustion chamber  22  communicates between intake manifold  24  and exhaust manifold  26  via a respective intake valve  28  and an exhaust valve  30 . Intake manifold  24  is also shown having fuel injector  32  coupled thereto for delivering liquid fuel in proportion to the pulse width of signal (FPW) from controller  12 . The fuel quantity together with the amount of air mass in the intake manifold  24  defines the air/fuel ratio directed into combustion chamber  22 . Those skilled in the art will also recognize that engine may be configured such that the fuel is injected directly into the cylinder of the engine in a direct injection type system. 
     A catalyst  34  is coupled to exhaust manifold  26  through exhaust system  36 . Catalyst  34  is used to reduce tail pipe emissions by performing reduction and oxidation reactions with the combustion gasses leaving cylinder  22  through exhaust valve  30 . 
     Controller  12  is shown as a conventional microcomputer including a microprocessing unit (CPU)  38 , input/output ports  40 , read-only memory  42 , random access memory  44 , and a conventional data bus  46  therebetween. 
     Controller  12  is shown receiving various signals from sensors coupled to engine  10 . The various sensors may include a mass airflow sensor  47  used to provide an air mass signal to controller  12 . A manifold absolute pressure (MAP) sensor that generates manifold absolute pressure may be used in place of mass airflow sensor. An engine speed sensor  48  is used to generate an engine speed signal corresponding to the rotational speed of the crankshaft. An exhaust gas oxygen sensor  50  positioned upstream of catalyst  34  provides a signal corresponding to the amount of oxygen in the exhaust gas prior to the catalyst. One suitable example of an exhaust gas oxygen sensor is a UEGO sensor. A second exhaust gas oxygen sensor  52  may be coupled to the exhaust system after catalyst  34 . One suitable example of an UEGO sensor downstream of catalyst  34  is a heated exhaust gas oxygen sensor. Catalyst  34  may also have a temperature sensor  54  coupled thereto. Catalyst temperature sensor  54  provides an operating temperature signal for the catalyst to controller  12 . Although a physical sensor  54  is illustrated, sensor  54  may also indirectly determine a temperature of the catalyst from other sensed inputs. The temperature of the catalyst may be estimated based upon the various engine operating conditions. In particular, catalyst temperature may be estimated using on a normal estimated temperature based on engine operating conditions that represent the catalyst temperature under normal conditions increased by a change in temperature based on the various operating conditions such as engine speed or load. 
     A throttle body  56  having a throttle plate  58  and a throttle position sensor  60  is illustrated. Throttle position sensor  60  provides controller  12  with an electrical signal corresponding to the desired driver demand. 
     A fuel system  66  is coupled to engine  10  through fuel injector  32 . Fuel injector  32  receives fuel from fuel tank in a conventional manner such as through the use of a fuel pump (not shown). A fuel vapor recovery system  70  is shown coupled between fuel tank  68  and intake manifold  24  via a purge line  72  and a purge control valve  74 . A canister  76  is coupled to purge line  72 . Canister  72  absorbs fuel vapors from the fuel tank  68  and stores them in activated charcoal contained within canister  76 . Purge control valve  74  is controlled by controller  12 . Of course, those skilled in the art will recognize that a separate controller may be used to control the valve  74 . Valve  74  may, for example, comprise a pulse width actuated solenoid valve having a substantially cross-sectional area. Of course, a valve having a variable orifice may also be used. 
     During a fuel vapor purge, air is drawn through canister  76  through an inlet vent  78  absorbing hydrocarbons from the activated charcoal. The mixture of purged air and absorbed vapors is then inducted into intake manifold  24  via purge control valve  74 . A purge flow sensor  80  provides feedback to controller  12  as to the volume or flow rate of the purge. 
     Referring now to FIG. 2A, a plot of normalized load change versus the lambda excursion due to the air path dynamics is illustrated. The plot is referred to as the air model. 
     Referring now to FIG. 2B, the change in purge flow/air mass is illustrated with respect to the air/fuel ratio excursion (Δλ p ). This plot is referred to as the purge model. 
     Referring now to FIG. 2C, the fuel multiplier (m) is plotted versus the air/fuel ratio lambda excursion (Δλ total ). The total takes into consideration purge model and the air model in the preceding figures. 
     Each of the plots shown in FIGS. 2A,  2 B, and  2 C may be experimentally determined for each engine type. Those skilled in the art will recognize that the experimental results used to determine the plots illustrated may be derived from on road and laboratory environments. 
     Referring now to FIG. 3, a block diagrammatic view of control system  90  according to the present invention is illustrated. Control system  90  includes a feed forward air/fuel controller  92 , a flow purge control logic  94 , and steady state gain models  96 . Steady state gain models  96  are coupled to feed forward controller  92 . Feed forward controller  92  is coupled to flow purge control logic  94 . Purge control logic  94  is coupled to steady state gain models  96 . Feed forward controller  92  determines a fuel pulse width (FPW) that is compared to feedback from a feedback controller  98 . The fuel pulse width is coupled to engine  10  for which the fuel pulse width in combination with the air charge as measured by mass air flow sensor  47 . Oxygen sensor  100  monitors the amount of oxygen in the exhaust gas which in turn may be used to determine the catalyst efficiency. Oxygen sensor  100  may be one of the oxygen sensors such as a UEGO sensor  50  or the HEGO sensor  52  shown in FIG.  1 . Of course, a combination of the two sensors may also be used. By monitoring the amount of oxygen in the exhaust gas, feedback controller  98  can determine how well the feed forward controller predicted the required change in the fuel pulse width. The feedback error signal is zero when the feed forward controller precisely predicted the lambda excursion. When the feedback from feedback controller  98  is large, adaptation, as will be further described below, may be performed. 
     Referring now to FIGS. 4 and 5, the operation of the feed forward controller is illustrated in FIG. 4, and the fueling control process is described in the flow chart in FIG.  5 . The system starts at block  116 . In step  118 , because the models operate in normalized domains, it is necessary to store the current load (LOAD), normalized purge flow (PV_flow), and fuel pulse width (fp). The fueling control process is initialized during cranking. At a designated time during the cranking process, the instantaneous cranking fuel pulse width (as determined by the cranking algorithm) and the instantaneous load and purge volume measurements are stored, thus initializing the controller variables of current load and current fuel pulse width. The system monitors a change in load and a change purge flow in step  120 . In step  122 , a change in load is determined by the addition block  124  and division block  126  of FIG.  4 . The input to addition block  124  determines the change in load (Δ LOAD) by subtracting (LOAD nom −LOAD) and dividing the result by LOAD nom  in block  126 . When a change in air charge (load) is determined in step  120  as indicated by the mass-air-flow sensor corresponding to the driver throttle command, an appropriate fuel pulse width multiplier is calculated in step  122  by air model  128  to offset the predicted lambda excursion (Δλ a   − ) as a result in the relative change in air mass to the cylinder (i.e. Δλ a =f(Δ LOAD/LOAD nom )). 
     In step  130 , when a change in purge flow is indicated (by a change in the duty cycle of the vapor management valve) a multiplier is calculated to offset the predicted lambda excursion (Δλ p ) resulting from a change in purge flow into the intake manifold (i.e. Δλ p =f(Δ PV/air_mass)). A change in purge volume is determined in the model by addition block  132  and division block  134 . The PV/air_mass nom  is subtracted from the instantaneous purge volume PV/air_mass and is divided by the purge flow, PV/air_mass . The change is determined by purge model  136 . A total predicted lambda excursion (Δλ a +Δλ p =Δλ total ) is determined in step  138  by summing block  140  of FIG.  4 . This total with the lambda excursion in step  138  from fuel model  142  (Δλ f =Δλ total ) is solved using the fuel model (Δλ f =f(m)) for m in step  144 . This multiplier (m) is inverted and applied to the current fuel pulse width (fp nom ) to determine a new fuel pulse width (fp new ) for engine  10  in step  146 . This is performed in FIG. 4 by multiplier block  148 . The feedback loop with feedback controller  98  of FIG. 3 generates a fuel pulse width correction that corrects for any errors in the feed forward control. This delta fuel pulse width is added to the feed forward pulse width at summing junction  101  of FIG.  3 . 
     In step  150 , once steady state has been reached, adaptation logic is used to change the models, i.e., the LOAD/Δ LOAD table, to restore the performance of the feed forward controller. The process then repeats in step  118 . 
     Advantageously, the logic set forth above allows both models to be adapted routinely without biased treatment of either the air or purge model. This is particularly important for the purge model which needs continual adaptation to respond to changes in the fuel vapor content in the purge flow. 
     Referring now to FIG. 6, adaptation of the air/fuel model is performed using a recursive least squares algorithm (RLS). As can be seen, the original model line  160  (such as the A load/load versus Δλ a  of FIG. 2A) is illustrated along with various data points  162 A,  162 B,  162 C,  162 D, and  162 E. During an adaptation window  164 , a point of error  166  is determined. By factoring in the previous points  162 A- 162 E, the point in error using the recursive least squares method can determine a revised model illustrated by dash line  168 . Thus, each model can be updated during the operation of the vehicle which compensates for various conditions such as wear and catalyst life. Of course, those skilled in the art will recognize the other plots shown in FIGS. 2B and 2C may be modified in a similar manner. 
     While particular embodiments of the invention have been shown and described, numerous variations and alternate embodiments will occur to those skilled in the art. Accordingly, it is intended that the invention be limited only in terms of the appended claims.