Abstract:
To perform the proper control conforming to the intent of a driver of an automotive vehicle under any condition which is encountered by the vehicle, optimum control methods are preliminarily classified in accordance with categories relating to conditions of the vehicle and categories relating to intents of the driver and the classified optimum control methods are stored in a memory, thereby selecting one of the control methods corresponding to the combination of the categories to which the vehicle condition and the driver&#39;s intent detected during the running of the vehicle belong.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a method for controlling a fuel injection system and an ignition system in an internal combustion engine, and more particularly to a control method for the internal combustion engine of an automotive vehicle which is well suited to meet the driver&#39;s various requirements relating to the driving of the vehicle. 
     Heretofore known electronic fuel injection control systems employ a method of intermittently supplying the fuel in an amount corresponding to the intake air flow rate and also varying the fuel quantity during the period of acceleration and deceleration (refer the below-mentioned (1) and (2)). During constant speed driving, this method can supply the engine with an amount of air and a fuel quantity which are proportional to the load and therefore there is no inconvenience. However, the method is disadvantageous in that the engine cannot be controlled properly during transient conditions, e.g., times of acceleration and deceleration. 
     As described above, the conventional control systems have been unable to provide satisfactory functions to meet the highly sophisticated and diversified requirements relating to driving performance. On the other hand, while torque servo controls and speed servo controls are proposed (e.g., the below-mentioned techniques (3) and (5)) to meet sophisticated requirements, no satisfactory consideration has been given to an overall control ensuring proper control under all conditions which are encountered by the vehicle. 
     Note that the prior art techniques relating to these types of systems include the following, for example. 
     (1) IDEI: “The Engine Controls”, Institute of Electrical Engineers of Japan Journal Vol. 101, No. 12, P. 1148 (December 1981) . . . Controls by Microcomputers; This relates to table look-up systems. 
     (2) NAGAYAMA et al: Centralized Control of Engine by Microcomputers, Systems and Controls, Vol. 24, No. 5, P. 306 (May 1980); This relates to flow charts of engine operations, fuel injection control, ignition timing control and idling speed control. 
     (3) T. TABE et al: On the Application of Modern Control Theory to Automotive Engine Control, IECOM &#39;85; This relates to torque servos. 
     (4) JP-A-57-73836 
     (5) ITO: “Fuel Economy Optimalizing Control System with Compound Control Action on Engine and Transmission”, Automotive Engineering, February 83; This relates to speed servos. 
     The above-mentioned conventional techniques have failed to give due consideration in comprehensively grasping as a system the control of the engine on a vehicle. Thus, there have been a lack of engine control methods which could meet all the situations in which the vehicle is to be used and the difficulty to establish the necessary parameters for such engine control methods has been a disadvantage. 
     One reason is that the conventional engine control methods are made up of static models despite the fact that the conditions which are encountered by a vehicle are a repetition of steady-state operations, e.g., the constant speed running and idling operation and the transient state operation such as acceleration and deceleration. Moreover, the requirements for the behaviour of the vehicle during the transient conditions have become increasingly severe on the part of the users of the vehicles. As a result, even if measuring devices are installed to observe the transient conditions, their full utilization cannot be ensured by the static model. 
     In the case of the conventional methods in which the static control model is compensated for the transient conditions, a great deal of manhours are required to materialize and adjust an engine control method for each of different types of vehicles which are diversely different in vehicle characteristics, measuring devices, actuators, etc. 
     SUMMARY OF THE INVENTION 
     With a view to overcoming the foregoing deficiencies in the prior art, it is an object of the invention to provide a method of controlling an internal combustion engine mounted on a vehicle in which different vehicle conditions and driver&#39;s different intents are respectively discriminated and divided into categories so as to select a proper one of a plurality of engine control methods corresponding to each of various combinations of the categories. 
     To adapt the dynamic characteristic of the vehicle to the sensitivity or fancy of the driver, it is only necessary to discriminate and classify the preferences of the driver into certain preference modes, such as, sporty, luxury and economy modes of driving and change the parameters of the respective control methods to suit the corresponding modes. To realize the selection of the engine control methods corresponding to the above discrimination and classification, it is only necessary to develop the software of the computer incorporated in the engine control system in such a manner that a higher priority level is allocated to allow execution of the condition discriminating and classifying function in preference to the other functions. 
     The discrimination and classification of the vehicle&#39;s conditions and driver&#39;s intents are performed in the following way. The conditions of the vehicle can be detected in terms of the vehicle speeds and vehicle speed changes. The driver indicates an intent concerning the driving by engaging the torque transmission mechanism (the clutch and the transmission) and depressing the brake pedal or the accelerator pedal. In other words, the driver indicates his intent in correspondence to the situation of the vehicle by selectively depressing the two pedals. The intent is represented by the angles and angular velocities of the pedals and their time series loci. The conditions of the vehicle and the intents of the driver can be detected in detail in accordance with the measured values from a certain prior time up to the present time as to the vehicle speed and its time rate of change and the angle and angular velocity of the brake and accelerator pedals. The angular velocity of the accelerator pedal is equivalent to the acceleration rate {dot over (θ)}ac in FIG.  4 . In addition, by utilizing these measured values, it is possible to estimate the condition of the vehicle and the intent of the driver and predict the future condition of the vehicle. 
     As regards the construction of the running controls of the vehicle, as will be described later with reference to the illustrated embodiments, there are a method of realizing the controls by a cascade connection of torque servo system, speed servo system and tracking servo system and another method of preparing the previously mentioned various engine control methods in a parallel manner. 
     The method of determining the preferences of the driver for vehicle operation may, for example, be to provide three selector switches respectively corresponding to the “sporty”, mode placing emphasis on drivability, “luxury” mode placing emphasis on driving comfortability and “economy” mode placing emphasis on practicality so that the parameters of each engine control method are changed in response to the selection of one of the selector switches. 
     The computer used for realizing the abovementioned method may be of the high type speed and the operation program may be prepared such that the condition discrimination and the selection of the engine control methods are effected most preferentially. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram showing an embodiment of the invention. 
     FIG. 2 is a block diagram showing another embodiment of the invention. 
     FIG. 3 is a block diagram showing an exemplary construction of the computer program used in the embodiment of FIG.  1 . 
     FIG. 4 is a diagram showing the relation between the vehicle conditions and the driver&#39;s intent and the respective engine control methods. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The principle of the present invention will now be described first with reference to FIG.  4 . 
     FIG. 4 shows the discrimination and classification of the vehicle conditions and driver&#39;s intent and engine control methods corresponding to the respective categories. 
     The vehicle conditions are roughly divided into a rest condition (V=0) and a running condition (V&gt;0). The driver&#39;s intent is discriminated on the basis of six different conditions including the operation state of the torque transmission mechanism (clutch) the depression of the brake pedal (breaking, θbr&gt;0), non-depression of the brake pedal (θbr=0) and the accelerator pedal (coasting, θac=0) the depression of the accelerator pedal (acceleration, the θac≧θaca) the depressed accelerator pedal (steady running, θacd&lt;θac&lt;θaca) at rest steady running, {dot over (θ)}acd&lt;{dot over (θ)}ac&lt;{dot over (θ)}aca) and the restored accelerator pedal (deceleration, {dot over (θ)}ac≦{dot over (θ)}acd). 
     When the torque transmission mechanism is on (engaged) and the accelerator pedal is depressed, a control for the acceleration requirement is performed ( in FIG.  4 ). With the vehicle running, when the accelerator pedal is released and the brake pedal is depressed, a deceleration control is performed ( in FIG.  4 ). At this time, if the idle switch is on (which indicates that the acceleration pedal is released) and the engine speed is excessively high, a fuel cut-off control is performed ( in FIG.  4 ). 
     In the running condition, if the vehicle is neither accelerated nor decelerated, an air-fuel ratio control is performed to maintain the air-fuel ratio at a desired value ( in FIG.  4 ). 
     When the torque transmission mechanism is off, an idle speed control comes into action to control the engine speed to maintain it at a desired value ( in FIG.  4 ). At this time, if the accelerator pedal is depressed, the switching to the previously mentioned air-fuel ratio control is effected despite the fact that the engine is racing. 
     The method of discriminating and classifying the conditions of the vehicle and the intents of the driver to select the proper engine control method is well suited to progressively deal with the diverse requirements of the user of the vehicle and the introduction of new techniques which meet the requirements. To the design and development engineer as well as persons who attend matching of the engine control methods with the actual vehicle (the adjustment of the parameters), this means advantages that it is necessary to understand only the engine control methods corresponding to the required categories, that a modification of the computer program requires only the modification of some modules and so on. 
     An embodiment of the invention will now be described with reference to FIG.  1 . The block diagram of FIG. 1 comprises a condition discriminating unit and cascaded control systems operable in response to the outputs of the former. 
     The conditions discriminating unit  1  detects the conditions of a vehicle in terms of a vehicle speed v, engine speed N, engine output torque T and a distance L between the vehicle and an obstacle ahead or the preceding vehicle and it also detects the intent of the driver in accordance with the changes in time (dynamic changes) obtained by operating on a signal  20  indicative of the brake pedal angle θ br , a signal  19  indicative of the accelerator pedal angle θ ac  and their past values. In accordance with these detection results and the preference of the driver, a determination is made as to which of the engine control methods is required and the decision of the construction of the cascade-connected running control systems, the selection of parameters and the modification of their values are performed. 
     The running control systems include the torque servo system, speed servo system and tracking servo system which are cascaded from the inner side near to an engine  2  so as to control its speed N and torque T. 
     The supply of fuel to the engine  2  is effected by a fuel injection control system  3  and the ignition timing is controlled by an ignition timing control system  4 . 
     A torque control mechanism  5  determines fuel quantity and ignition timing corresponding to a torque deviation required by the control systems and the results are applied to the fuel injection control system  3  and the ignition timing control system  4 . While the ignition timing control system  4  operates in accordance with the ignition timing determined by the torque control mechanism  5  at the low speed operation and the constant speed driving, during the transient period the ignition timing can be controlled directly if the condition discriminating unit  1  requires a rapid surge preventive measure. 
     When the torque servo system is selected by the condition discriminating unit  1 , its reference value is applied to a torque reference setup unit  6  from the condition discriminating unit  1 . Thus, the input to the torque control mechanism  5  represents the difference value between the torque reference value and the measured value of the engine torque. A torque servo system selector switch  7  is selected in accordance with the result of the decision in the condition discriminating unit  1 . A torque measuring device  8  performs the operation of engineering value conversion and smoothing on the measured value of the torque. Where the upstream speed servo system is selected, the input to the torque control mechanism  5  is the output of a speed control mechanism  9 . 
     Where the driving involves a frequent repetition of acceleration and deceleration, the driver demands an increase in the torque by depressing the accelerator pedal and commands a decrease in the torque by releasing the depression. Thus, the condition discriminating unit  1  applies a torque desired value corresponding to the movement of the accelerator pedal and engine speed. Alternatively, a torque deviation may be directly applied to the torque controlling mechanism  5 . 
     When the condition discriminating unit  1  selects the idle speed control (ISC) or the driver selects the constant speed driving (cruising) control, the condition discriminating unit  1  selects a selector switch  10  so that the vehicle speed reference value applied to a speed reference setup unit  11  from the condition discriminating unit  1  is compared with the actual measured vehicle sped and the speed controlling mechanism  9  controls the vehicle speed to approach the reference value. The actual vehicle speed is measured by a vehicle speed measuring device  13  in which the axle speed derived from the engine  2  through a gear  12  is corrected for variation in the tire diameter, etc., and the resulting time series data is smoothed out. 
     Even if the cruise control has been selected, when the driver depresses the accelerator pedal, the switch  7  is turned on and the switching to the torque servo system is effected. 
     Where the vehicle is provided with a sensor for measuring the distance from an obstalcle  obstacle ahead, a signal  17   from a cruising speed selector switch (not shown) 17 is selected so that when the distance from the preceding vehicle is less than an allowable value, the switching is made from the speed servo system to the tracking servo system. 
     A tracking control mechanism  14  determines an increase or decrease in the vehicle speed in accordance with the difference between the measured value from a distance sensor  15  for measuring the distance from an obstacle ahead and the predetermined following distance reference value corresponding to the vehicle speed and the result is applied to the speed control mechanism  9 . The following distance reference value is determined by the condition discriminating unit  1  and sent to a following distance reference setup unit  16 . This value is utilized for the calculation of a distance difference. 
     The following Table 1 shows the correspondence between the engine control methods to be selected by the condition discriminating unit  1  and the construction of the cascade control system. 
     
       
         
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
             
             
               
                   
                   
               
               
                   
                 Construction 
               
             
          
           
               
                   
                 ENGINE 
                 Torque 
                 Speed 
                 Tracking 
               
               
                   
                 CONTROL 
                 Servo 
                 Servo 
                 Servo 
               
               
                   
                 METHODS 
                 System 
                 System 
                 System 
               
               
                   
                   
               
               
                   
                 Acceleration Control 
                 ∘ 
                 Δ 
                 Δ 
               
               
                   
                 Deceleration Control 
                 ∘ 
                 Δ 
                 Δ 
               
               
                   
                 Fuel Cut-Off Control 
                 ∘ 
                 — 
                 — 
               
               
                   
                 Air-Fuel Ratio 
                 ∘ 
                 ∘ 
                 ∘ 
               
               
                   
                 Control 
               
               
                   
                 Idle Speed Control 
                 — 
                 ∘ 
                 — 
               
               
                   
                   
               
               
                   
                 Explanation  
               
               
                   
                 ∘ Great contribution  
               
               
                   
                 Δ Moderate contribution  
               
               
                   
                 — Small contribution  
               
             
          
         
       
     
     When the results of the condition discrimination indicates that the acceleration or deceleration control is needed, the torque servo system functions principally. At this time, the speed servo system also functions if the constant speed driving is being selected and also the tracking servo system functions if the distance sensor is in operation. The fuel cut-off control is performed within the range of the torque servo system. The air-fuel ratio control is performed during the torque servo system for the purpose of improving the fuel consumption and reducing the exhaust gas emission. The air-fuel ratio control functions effectively even during the constant speed driving as well as the tracking driving. In the case of the idle speed control, the speed servo system having the idle speed as the reference value functions. 
     The following Table 2 shows the results of the preference mode selection or input signals  18  to the condition discriminating unit  1 . 
     
       
         
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
             
             
               
                   
                   
               
               
                   
                 Control System 
               
               
                   
                 Construction 
               
             
          
           
               
                   
                   
                 Torque 
                 Speed 
                 Tracking 
               
               
                   
                 Preference 
                 Servo 
                 Servo 
                 Servo 
               
               
                   
                 Node 
                 System 
                 System 
                 System 
               
               
                   
                   
               
               
                   
                 Sporty 
                 ∘ 
                 — 
                 — 
               
               
                   
                 Luxury 
                 ∘ 
                 ∘ 
                 ∘ 
               
               
                   
                 Economy 
                 ∘ 
                 Δ 
                 — 
               
               
                   
                   
               
               
                   
                 ∘ Great contribution  
               
               
                   
                 Δ Moderate contribution  
               
               
                   
                 — Small contribution  
               
             
          
         
       
     
     As will be seen from Table 2, each of the sporty, luxury and economy modes corresponds mainly through changing of the control parameters of the torque servo system. As regards the “luxury” mode, coupled with the provision of the cruise control function and the distance sensor, the speed servo system and the tracking servo system function effectively. 
     In the case of the “economy” mode, while the speed servo system may be used jointly, a control algorithm is used which ensures saving of the fuel consumption even if the degree of the cruise control is reduced. 
     FIG. 2 shows another embodiment of the invention which has the same purposes as the embodiment of FIG.  1 . FIG. 2 shows a construction in which the proper engine control method is selected from alternatives for the engine control methods in accordance with the discrimination result of the condition discriminating unit  1 . The alternatives of the engine control methods include basically an acceleration control  21 , deceleration control  22 , fuel cut-off control  23 , air-fuel ratio control  24  and idle speed control  25 . Each of these five engine control methods is responsive to the results of calculations to supply a fuel quantity and an ignition timing to a fuel injection control system  3  and an ignition timing control system  4 , respectively. 
     Where the acceleration control, the deceleration control or the fuel cut-off control is selected, rapid application of the control may have the danger of causing a surging phenomenon depending on the condition of the vehicle and therefore a predictive calculation is made on the basis of the vehicle condition and the selected control method. If the occurrence of a surging phenomenon is predicted, the air fuel-ratio control is selected or alternatively the parameter values of the already selected engine control method are changed. 
     The computer is essential for materializing the overall control relating to the engine as shown in FIG.  1 . FIG. 3 shows the construction of the computer program. 
     The program shown in FIG. 3 is started at an interrupt step  31  and then at an interrupt decision step  32  a branching is made to a periodic interrupt step  33  or an end of A/D conversion interrupt step  35  which takes place after an A/D conversion start step  34  initiated by the interrupt step  33 . After the end of A/D conversion interrupt step  35 , the condition discrimination described in connection with FIG. 1 is performed and the proper engine control method is selected. In accordance with the selection result, a task distributing step  36  calls any of the following tasks. Assigned to a task level  0  are the ignition timing control  4 , the fuel injection control  3  and the torque control  5  for rapid response purposes. Assigned to a task level  1  are the speed control  9 , the tracking control  14 , etc. Assigned to a task level  2 , et seq., are the other programs which are allowed to respond more slowly. 
     From the present program construction point of view, there is a feature that when the vehicle condition and the driver&#39;s intent are subjected to A/D conversion and inputted, a condition discriminating step is performed thereby rapidly responding to the transient condition. 
     In accordance with the present invention, by virtue of the fact that the condition of a vehicle and the driver&#39;s intent can be detected rapidly from moment to moment and moreover the proper engine control method to be used in response to the detection results can be determined accurately, there is the effect of improving the driving performance, ensuring effective utilization of the engine performance, and rapidly developing engine control methods matched to different engine performances of different vehicles with the improved productivity of software therefor.