Abstract:
A control device of an engine includes means for detecting an efficiency of the engine, means for detecting a combustion stability of the engine, means for detecting an HC discharged quantity, and means for executing a notification. The notification is executed when the efficiency of the engine and the combustion stability of the engine do not fall in a predetermined region A 1 . The predetermined region A 1  is a range of the efficiency of the engine and the combustion stability of the engine. The HC discharged quantity at the time of engine start is a predetermined value or less.

Description:
TECHNICAL FIELD 
     The present invention relates to an exhaust performance diagnosis/control device of an engine, and relates specifically to a control device that diagnoses exhaust deterioration at the time of engine start or reduces exhaust gas at the time of start. 
     BACKGROUND ART 
     Against the background of global environmental problems, reduction of exhaust gas is required for automobiles. Technologies on a diagnosing function monitoring exhausting performance in a practical use environment on a real-time basis and notifying a driver of deterioration of the exhaust performance to a constant level or above have been developed until now. 
     By highly efficiently utilizing a catalyst furnished in an exhaust pipe, nearly 100% of exhaust gas components of HC, CO, NOx can be purified. Because a catalyst is activated and exerts purification performance when its temperature becomes 200-300° C. or above, exhaust performance from the time of engine start to activation of the catalyst predominantly determines exhaust performance of the engine. Accordingly, monitoring of the exhaust performance at the time of engine start on a real-time basis becomes important. At the time of engine start, HC performance is particularly important. In JP-A No. 2007-170363, a means is disclosed which diagnoses presence/absence of abnormality of a rapid catalyst warm-up control means based on a ratio of engine load and engine speed during idling operation. 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2007-170363 
       
    
     SUMMARY OF INVENTION 
     Technical Problems 
     As described above, it is important to detect the HC quantity discharged until activation of the catalyst. A technology is common in which, in order to activate a catalyst rapidly, by intentionally delaying ignition timing, efficiency of an engine is made deteriorate and exhaust gas temperature is raised. At the time of idling operation, because engine load (intake air quantity) means supplied energy and engine speed means output, a ratio of the engine speed and the intake air quantity expresses efficiency of the engine. Accordingly, as shown in  FIG. 14 , regardless of rich or lean of the air fuel ratio, the time to activation of the catalyst can be determined from the ratio of the engine speed and the intake air quantity. Here, the engine efficiency index is the ratio of the engine speed and the intake air quantity. On the other hand, even when the time until activation of the catalyst is constant, according to the HC quantity discharged from the engine during that time, the HC quantity discharged until activation of the catalyst changes.  FIG. 15  shows the HC discharged quantity [g/s] relative to the engine efficiency index. Here, the HC discharged quantity shows the HC quantity [g] discharged from the engine per 1 s. The HC discharged quantity changes according to the air fuel ratio. Even when a fuel injection signal is constant, the combustion air fuel ratio varies due to variation of fuel characteristics, age-based deterioration of a fuel injection valve and the like, and therefore the HC quantity discharged from the engine also varies. In order to detect the HC quantity discharged until activation of the catalyst, it is necessary to detect not only the time until activation of the catalyst but also the HC quantity discharged from the engine. 
     Solution to Problems 
     As shown in  FIG. 1 , the present invention is a control device of an engine including a means that detects efficiency of the engine and a means that detects combustion stability of the engine. 
       FIG. 16  shows the relation of stability of combustion against an air fuel ratio. Here, the stability of combustion shows the standard deviation of the angular acceleration of an engine. The energy efficiency indices are shown being classified according to respective ranges shown in the drawing. The reason the stability of combustion varies in an equal air fuel ratio is because ignition timing changes. When the energy efficiency index is determined, the air fuel ratio is determined uniquely from the stability of combustion. Accordingly, when both of the energy efficiency index and the combustion stability are used, the air fuel ratio can be obtained, and the HC discharged quantity shown in  FIG. 15  can be determined uniquely. When the HC discharged quantity [g] until activation of the catalyst is approximated by the product of the time [s] until activation of the catalyst multiplied by the HC discharged quantity during that time [g/s], as shown in  FIG. 15 , the HC discharged quantity can be determined uniquely from the energy efficiency index and the combustion stability (the standard deviation of angular acceleration). 
     As described above, it is possible to quantitatively detect the HC discharged quantity until activation of the catalyst from both of the efficiency of the engine and the combustion stability of the engine. The minimum constitution thereof is hereby shown. 
     Also, as shown in  FIG. 2  with the premise of the constitution shown in  FIG. 1 , a preferable aspect is the control device of an engine further including a means that detects an HC discharged quantity at the time of engine start based on efficiency of the engine and combustion stability of the engine. As described above, the HC discharged quantity until activation of the catalyst is detected quantitatively from both of the efficiency of the engine and the combustion stability of the engine. 
     Also, as shown in  FIG. 3  with the premise of the constitution shown in  FIG. 1  or  FIG. 2 , a preferable aspect is the control device of an engine further including a means that executes notification when the efficiency of the engine and the combustion stability of the engine do not fall in a predetermined region A 1 . The means is provided for example which notifies a driver of an event that the HC discharged quantity has become a predetermined value or more (the exhaust performance has deteriorated) when either the efficiency of the engine or the combustion stability of the engine has deviated from the region A 1  because it is possible to quantitatively detect the HC discharged quantity until activation of the catalyst from both of the efficiency of the engine and the combustion stability of the engine as described above. 
     Also, as shown in  FIG. 4  with the premise of the constitution shown in  FIG. 3 , a preferable aspect is the control device of an engine in which the predetermined region A 1  is a range of the efficiency of the engine and the combustion stability of the engine in which the HC discharged quantity at the time of engine start is a predetermined value or less. It is clearly stipulated hereby that the region where the energy efficiency of the engine and the combustion stability of the engine where the HC discharged quantity becomes a predetermined value or less are present is made A 1 . 
     Also, as shown in  FIG. 5  with the premise of the constitution shown in any one of  FIGS. 1-4 , a preferable aspect is the control device of an engine in which the efficiency of the engine is obtained based on a ratio of an engine speed and an intake air quantity of the engine at the time of idling operation. As described above, at the time of idling operation, because the intake air quantity of the engine means the supplied energy and the engine speed means the output, the ratio of the engine speed and the intake air quantity expresses the efficiency of the engine. 
     Also, as shown in  FIG. 6  with the premise of the constitution shown in any one of  FIGS. 1-5 , a preferable aspect is the control device of an engine in which the combustion stability of the engine is obtained based on a variation degree of angular acceleration of the engine. There is a correlation between the angular acceleration and the pressure inside the cylinder. Because the stability of combustion is the reproducibility of the pressure inside the cylinder, the combustion stability of the engine can be obtained indirectly according to the variation degree of the angular acceleration. As described above, the standard deviation, the variance and the like can be conceived with respect to the variation degree. 
     Also, as shown in  FIG. 7  with the premise of the constitution shown in any one of  FIGS. 1-6 , a preferable aspect is the control device of an engine further including a means that controls the engine so that the efficiency of the engine and the combustion stability of the engine fall in a predetermined region A 2 . Because the HC discharged quantity until activation of the catalyst is determined quantitatively from the efficiency of the engine and the combustion stability of the engine as described above, when the operation state of the engine is controlled so that the efficiency of the engine and the combustion stability of the engine fall in a predetermined region, the HC discharged quantity at the time of start can be controlled quantitatively. 
     Also, as shown in  FIG. 8  with the premise of the constitution shown in any one of  FIGS. 1-7 , a preferable aspect is the control device of an engine further including a means that controls at least either one of an air fuel ratio or ignition timing of the engine so that the efficiency of the engine and the combustion stability of the engine fall in the predetermined region A 2 . As described in the explanation above, when the operation state of the engine is controlled so that the efficiency of the engine and the combustion stability of the engine fall in the predetermined region, the HC discharged quantity at the time of start can be controlled quantitatively. As operational parameters for the engine, the air fuel ratio and the ignition timing are hereby clearly stipulated. 
     Also, as shown in  FIG. 9  with the premise of the constitution shown in either  FIG. 6 or 7 , a preferable aspect is the control device of an engine in which the control of the engine is stopped when the combustion stability of the engine has become a predetermined value or more. As described in the explanation above, when the operation state of the engine is controlled so that the efficiency of the engine and the combustion stability of the engine fall in the predetermined region, the HC discharged quantity at the time of start can be controlled quantitatively. However, when the combustion stability of the engine has become a predetermined value or more (when the engine has become unstable) due to some disturbance in a process of controlling the efficiency of the engine to a predetermined region, securing the stability of the engine is given priority, and the engine control is stopped. 
     Also, as shown in  FIG. 10  with the premise of the constitution shown in  FIG. 8 , a preferable aspect is the control device of an engine in which, when the combustion stability of the engine has become a predetermined value or more, the air fuel ratio of the engine is controlled to a rich side, or the ignition timing of the engine is controlled to an advance side. As described in the explanation above, when the operation state of the engine is controlled so that the efficiency of the engine and the combustion stability of the engine fall in the predetermined region, the HC discharged quantity at the time of start can be controlled quantitatively. However, when the combustion stability of the engine has become a predetermined value or more (when the engine has become unstable) due to some disturbance in a process of controlling the efficiency of the engine to a predetermined region, in order to improve the stability of the engine, the air fuel ratio is controlled to the rich side or the ignition timing is controlled to the advance side so as to stabilize combustion. 
     Also, as shown in  FIG. 11  with the premise of the constitution shown in any one of  FIGS. 7-10 , a preferable aspect is the control device of an engine in which notification is executed when the combustion stability of the engine has become a predetermined value or more. As described in the explanation above, when the operation state of the engine is controlled so that the efficiency of the engine and the combustion stability of the engine fall in the predetermined region, the HC discharged quantity at the time of start can be controlled quantitatively. However, when the combustion stability of the engine has become a predetermined value or more (when the engine has become unstable) due to some disturbance in a process of controlling the efficiency of the engine to a predetermined region, for example, a means is hereby provided which notifies the driver of the event that the HC discharged quantity at the time of start has deteriorated because the HC discharged quantity cannot be controlled to a desired value. 
     Also, as shown in  FIG. 12  with the premise of the constitution shown in either  FIG. 3 or 4 , a preferable aspect is the control device of an engine further including a means that changes the predetermined region A 1  based on “an operation state of the engine” or “a diagnosis result of a means related to exhaust performance”. As described above, the HC discharged quantity at the time of start is determined quantitatively from the efficiency of the engine and the combustion stability of the engine. This is on the premise of a case the operation condition of the engine, the light-off performance of the catalyst and the like are constant. The predetermined region A 1  is hereby changed based on the diagnosis result of a means related to the exhaust performance such as the operation condition of the engine, the light-off performance of the catalyst and the like. 
     Also, as shown in  FIG. 13  with the premise of the constitution shown in either  FIG. 7 or 8 , a preferable aspect is the control device of an engine further including a means that changes the predetermined region A 1  based on “an operation state of the engine” or “a diagnosis result of a means related to exhaust performance”. That is, as described above, the HC discharged quantity at the time of start is determined quantitatively from the efficiency of the engine and the combustion stability of the engine. This is on the premise of a case the operation condition of the engine, the light-off performance of the catalyst and the like are constant. The predetermined region A 2  is to be changed hereby based on the diagnosis result of a means related to the exhaust performance such as the operation condition of the engine, the light-off performance of the catalyst and the like. 
     Advantageous Effects of Invention 
     According to the present invention, the HC discharged quantity at the time of start can be detected quantitatively from the efficiency of the engine and the combustion stability of the engine. Accordingly, deterioration of the HC discharged quantity at the time of start can be detected precisely and can be notified. Also, by controlling the efficiency of the engine and the combustion stability of the engine, the HC discharged quantity at the time of start can be controlled quantitatively and stable reduction of HC can be achieved. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a conceptual drawing showing a control device of an engine described in claim  1 . 
         FIG. 2  is a conceptual drawing showing a control device of an engine described in claim  2 . 
         FIG. 3  is a conceptual drawing showing a control device of an engine described in claim  3 . 
         FIG. 4  is a conceptual drawing showing a control device of an engine described in claim  4 . 
         FIG. 5  is a conceptual drawing showing a control device of an engine described in claim  5 . 
         FIG. 6  is a conceptual drawing showing a control device of an engine described in claim  6 . 
         FIG. 7  is a conceptual drawing showing a control device of an engine described in claim  7 . 
         FIG. 8  is a conceptual drawing showing a control device of an engine described in claim  8 . 
         FIG. 9  is a conceptual drawing showing a control device of an engine described in claim  9 . 
         FIG. 10  is a conceptual drawing showing a control device of an engine described in claim  10 . 
         FIG. 11  is a conceptual drawing showing a control device of an engine described in claim  11 . 
         FIG. 12  is a conceptual drawing showing a control device of an engine described in claim  12 . 
         FIG. 13  is a conceptual drawing showing a control device of an engine described in claim  13 . 
         FIG. 14  is a drawing showing the relation between the efficiency of the engine and the time until activation of the catalyst. 
         FIG. 15  is a drawing showing the relation between the efficiency of the engine and the HC discharged quantity. 
         FIG. 16  is a drawing showing the relation between the air fuel ratio and the stability of combustion. 
         FIG. 17  is a drawing showing the relation of the efficiency of the engine, the stability of combustion and the HC discharged quantity until activation of the catalyst. 
         FIG. 18  is an engine control system drawing in examples 1-3. 
         FIG. 19  is a drawing expressing the inside of a control unit in examples 1-3. 
         FIG. 20  is a block diagram expressing the total control in example 1. 
         FIG. 21  is a block diagram of a diagnosis permit unit in examples 1, 3. 
         FIG. 22  is a block diagram of an efficiency index calculation unit in examples 1-3. 
         FIG. 23  is a block diagram of an instability index calculation unit in examples 1-3. 
         FIG. 24  is a block diagram of an abnormality determination unit in examples 1, 3. 
         FIG. 25  is a block diagram expressing the total control in example 2. 
         FIG. 26  is a block diagram of a basic fuel injection quantity calculation unit in examples 2-3. 
         FIG. 27  is a block diagram of a control permit unit  1  in examples 2-3. 
         FIG. 28  is a block diagram of a basic fuel injection quantity correction value calculation unit in examples 2-3. 
         FIG. 29  is a block diagram of a control permit unit  2  in examples 2-3. 
         FIG. 30  is a block diagram of an ignition timing correction value calculation unit in example 2. 
         FIG. 31  is a block diagram expressing the total control in example 3. 
         FIG. 32  is a block diagram of an ignition timing correction value calculation unit in example 3. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Examples of the invention will be described in detail below. 
     Example 1 
       FIG. 18  is a system drawing showing the present example. In an engine  9  formed of multiple cylinders (4 cylinders here), air from the outside passes through an air cleaner  1 , goes through an intake manifold  4  and a collector  5 , and flows into cylinders. The air quantity flowing in is adjusted by an electronic throttle  3 . The air quantity flowing in is detected by an air flow sensor  2 . Also, the intake temperature is detected by an intake temperature sensor  29 . A signal of every 10° of the rotational angle of a crankshaft and a signal of every combustion period are outputted by a crank angle sensor  15 . A water temperature sensor  14  detects the cooling water temperature of the engine. Also, an accelerator opening sensor  13  detects the stepping amount of an accelerator  6 , and thereby detects required torque of a driver. 
     Respective signals of the accelerator opening sensor  13 , the air flow sensor  2 , the intake temperature sensor  29 , a throttle valve opening sensor  17  attached to the electronic throttle  3 , the crank angle sensor  15  and the water temperature sensor  14  are transmitted to a control unit  16  described below, the operation state of the engine is obtained from these sensor outputs, and main operation quantities of the engine of the air quantity, fuel injection quantity and ignition timing are calculated optimally. 
     The target air quantity calculated inside the control unit  16  is converted to a target throttle opening an electronic throttle drive signal, and is transmitted to the electronic throttle  3 . The fuel injection quantity is converted to an open valve pulse signal, and is transmitted to a fuel injection valve (injector)  7 . Also, a drive signal is transmitted to an ignition plug  8  so as to execute ignition at ignition timing calculated by the control unit  16 . 
     Injected fuel is mixed with air from the intake manifold, flows in to inside the cylinders of the engine  9 , and forms gas mixture. The gas mixture explodes by sparks generated by the ignition plug  8  at predetermined ignition timing, pushes down a piston by its combustion pressure, and becomes power of the engine. Exhaust gas after explosion is sent to a three way catalyst  11  through an exhaust gas manifold  10 . A part of the exhaust gas is circulated to the intake side through an exhaust gas circulation pipe  18 . The circulation quantity is controlled by an exhaust gas circulation quantity adjust valve  19 . 
     A catalyst upstream air fuel ratio sensor  12  is attached between the engine  9  and the three way catalyst  11 . A catalyst downstream O 2  sensor  20  is attached downstream of the three way catalyst  11 . 
       FIG. 19  shows the inside of the control unit  16 . Respective sensor output values of the air flow sensor  2 , the catalyst upstream air fuel ratio sensor  12 , the accelerator opening sensor  13 , the water temperature sensor  14 , the engine speed sensor  15 , the throttle valve opening sensor  17 , the catalyst downstream O 2  sensor  20 , the intake temperature sensor  29 , and a speed sensor  30  are inputted into the control unit  16 , are subjected to a signal processing such as noise removal and the like in an input circuit  24 , and are transmitted thereafter to an input/output port  25 . The value at the input port is stored in a RAM  23 , and is subjected to calculation processing inside a CPU  21 . A control program describing contents of calculation processes is written in a ROM  22  in advance. Values calculated according to the control program and expressing respective actuator working amounts are stored in the RAM  23  and are thereafter transmitted to the input/output port  25 . A work signal of the ignition plug is set with an ON•OFF signal that turns ON when a primary side coil inside an ignition output circuit is excited and turns OFF when not excited. The ignition timing is time when ON turns to OFF. A signal for the ignition plug set in the output port is amplified to a sufficient energy level required for combustion in an ignition output circuit  26 , and is supplied to the ignition plug. Also a drive signal of the fuel injection valve is set with an ON•OFF signal that turns ON when the valve opens and turns OFF when the valve closes, is amplified to an energy level sufficient to open the fuel injection valve by a fuel injection valve drive circuit  27 , and is transmitted to the fuel injection valve  7 . A drive signal achieving the target opening of the electronic throttle  3  is transmitted to the electronic throttle  3  through an electronic throttle drive circuit  28 . 
     Below, the control program written in the ROM  22  will be described.  FIG. 20  is a block diagram expressing the total control, and is formed of calculation units described below.
     Diagnosis permit unit ( FIG. 21 )   Efficiency index calculation unit ( FIG. 22 )   Instability index calculation unit ( FIG. 23 )   Abnormality determination unit ( FIG. 24 )   

     A flag (fp_diag) that permits diagnosis is calculated by “the diagnosis permit unit”. An engine efficiency index (Ind_ita) that is a ratio of an engine speed (Ne) and a suction air quantity (Qa) is calculated by “the efficiency index calculation unit”. An instability index (Ind_sta) that is a variation degree of the angular acceleration expressing instability of combustion is calculated by “the instability index calculation unit”. By “the abnormality determination unit”, whether or not the HC discharged quantity at the time of start is a predetermined value or less is determined from both values of the efficiency index (Ind_ita) and the instability index (Ind_sta), and, when the HC discharged quantity at the time of start is a predetermined value or more, an abnormality flag (f_MIL) is made 1. Below, the detail of respective calculation units will be described. 
     &lt;Diagnosis Permit Unit ( FIG. 21 )&gt; 
     By the present calculation unit, a diagnosis permit flag (fp_diag) is calculated which is specifically shown in  FIG. 21 . The initial value of fp_diag is made 0. When a predetermined time T 0  has elapsed after the rotational speed (Ne) changes from 0 to Ne&gt;K 0 _Ne, fp_diag is made 1. That is, when a predetermined time has elapsed after a state of engine stop and start of the engine, diagnosis is permitted. 
     &lt;Efficiency Index Calculation Unit ( FIG. 22 )&gt; 
     By the present calculation unit, the efficiency index (Ind_ita) is calculated which is specifically shown in  FIG. 22 . A ratio of the engine speed (Ne) and the suction air quantity (Qa) is made the engine efficiency index (Ind_ita). 
     &lt;Instability Index Calculation Unit ( FIG. 23 )&gt; 
     By the present calculation unit, the instability index (Ind_sta) is calculated which is specifically shown in  FIG. 23 .
     Difference of the engine speed (Ne) is calculated for every combustion period and is made d_Ne.   An absolute value of d_Ne is calculated and is made abs_d_Ne.   A weighted moving average value of abs_d_Ne is calculated and is made the instability index (Ind_ita).   

     A weighted index of a weighted moving averaging processing is determined according to the responsiveness required for diagnosis. 
     &lt;Abnormality Determination Unit ( FIG. 24 )&gt; 
     By the present calculation unit, the abnormality flag (f_MIL) is calculated which is specifically shown in  FIG. 24 .
     When the diagnosis permit flag (fp_diag) is 0, the abnormality flag (f_MIL) is made 0.   When the diagnosis permit flag (fp_diag) is 1, and when “the efficiency index (Ind_ita) is K 0 _ita or less” and “the instability index (Ind_sta) is K 0 _sta or more”, f_MIL is made 0. Otherwise, f_MIL is made 1.   

     As shown in  FIG. 17 , K 0 _ita and K 0 _sta are determined from the efficiency index and the instability index corresponding to the HC discharged quantity at the time of start that is made an abnormal level. Although an equal HC discharged quantity line is a curved line in  FIG. 17 , in order to facilitate mounting, it may be approximated by a straight line as the present example. According to required accuracy, it may be brought close to a curved line. Also, it may be changed based on the operation condition of the engine. It may be changed also based on a change (deterioration) of the light-off performance of the catalyst. More specifically, K 0 _ita is increased or K 0 _sta is reduced according to deterioration of the light-off performance of the catalyst. It is also possible to change both the parameters. 
     Example 2 
     In example 1, the HC discharged quantity at the time of start was diagnosed from the efficiency of the engine and the stability of the engine. In example 2, the engine is controlled so that the HC discharged quantity at the time of start becomes a predetermined value from the efficiency of the engine and the stability of the engine. 
       FIG. 18  is a system drawing showing the present example and is similar to that of example 1, and therefore detailed description thereof will be omitted.  FIG. 19  shows the inside of the control unit  16  and is similar to that of example 1, and therefore detailed description thereof will be omitted also. Below, a control program written in the ROM  22  in  FIG. 19  will be described.  FIG. 25  is a block diagram expressing the total control, and is formed of calculation units described below.
     Basic fuel injection quantity calculation unit ( FIG. 26 )   Control permit unit  1  ( FIG. 27 )   Instability index calculation unit ( FIG. 23 )   Basic fuel injection quantity correction value calculation unit ( FIG. 28 )   Control permit unit  2  ( FIG. 29 )   Efficiency index calculation unit ( FIG. 22 )   Ignition timing correction value calculation unit ( FIG. 30 )   

     By “the basic fuel injection quantity calculation unit”, a basic fuel injection quantity Tp 0  is calculated. By “the control permit unit  1 ”, a flag (fp_cont 1 ) is calculated which permits control for making the air fuel ratio lean based on the instability index (Ind_sta) after start. By “the instability index calculation unit”, the instability index (Ind_sta) is calculated which is a variation degree of the angular acceleration meaning instability of combustion. By “the basic fuel injection quantity correction value calculation unit”, a basic fuel injection quantity correction value (F_hos) for making the air fuel ratio lean is calculated. By “the control permit unit  2 ”, a flag (fp_cont 2 ) is calculated which permits control for retarding the ignition timing based on the efficiency index (Ind_ita) after the air fuel ratio is made lean. By “the efficiency index calculation unit”, the engine efficiency index (Ind_ita) is calculated which is a ratio of the engine speed (Ne) and the suction air quantity (Qa). By “the ignition timing correction value calculation unit”, an ignition timing correction value (Adv_hos) retarding the ignition timing is calculated. Below, the detail of respective calculation units will be described. 
     &lt;Basic Fuel Injection Quantity Calculation Unit ( FIG. 26 )&gt; 
     By the present calculation unit, the basic fuel injection quantity (Tp 0 ) is calculated. More specifically, it is calculated by an expression shown in  FIG. 26 . Here, Cy 1  expresses the cylinder number. K 0  is determined based on the specification of the injector (relation between the fuel injection pulse width and the fuel injection quantity). 
     &lt;Control Permit Unit  1  ( FIG. 27 )&gt; 
     By the present calculation unit, the control permit flag (fp_cont 1 ) is calculated which is specifically shown in  FIG. 27 . The initial value of fp_cont 1  is made 0. When a predetermined time T 1  has elapsed after the rotational speed (Ne) becomes Ne&gt;K 1 _Ne from 0, fp_cont 1  is made 1. That is, when a predetermined time has elapsed after a state of engine stop and start of the engine, leaning of the air fuel ratio is started. 
     &lt;Instability Index Calculation Unit ( FIG. 23 )&gt; 
     By the present calculation unit, the instability index (Ind_sta) is calculated which is specifically shown in  FIG. 23 , however, because it is same with that of example 1, detail description thereof will be omitted. 
     &lt;Basic Fuel Injection Quantity Correction Value Calculation Unit ( FIG. 28 ). 
     By the present calculation unit, the basic fuel injection quantity correction value (F_hos) is calculated which is specifically shown in  FIG. 28 .
     When fp_cont 1 =0, F_hos is made 1.0.   When fp_cont 1 =1, F_hos is reduced by K 1 _F stepwise until ind_sta≧K 1 _sta is achieved.   When fp_cont 1 =1 and fp_cont 2 =1, F_hos maintains a previous value.   

     K 1 _sta is made an instability index value equivalent to a target air fuel ratio. Also, it may be changed based on the operation condition of the engine. It may be changed also based on a change (deterioration) of the light-off performance of the catalyst. More specifically, K 1 _sta is increased according to deterioration of the light-off performance of the catalyst. 
     K 1 _F is a value that determines a leaning speed, and is determined taking responsiveness of the engine and the like also into account. 
     &lt;Control Permit Unit  2  ( FIG. 29 )&gt; 
     By the present calculation unit, the control permit flag  2  (fp_cont 2 ) is calculated which is specifically shown in  FIG. 29 .
     When fp_cont 1 =0 and ind_sta≧K 1 _sta, fp_cont 2  is made 1.   Otherwise, fp_cont 2  is made 0.   

     As described above, K 1 _sta is made the instability index value equivalent to the target air fuel ratio. 
     &lt;Instability Index Calculation Unit ( FIG. 22 )&gt; 
     By the present calculation unit, the efficiency index (Ind_ita) is calculated which is specifically shown in  FIG. 22 , however, because it is same with that of example 1, detail description thereof will be omitted. 
     &lt;Ignition Timing Correction Value Calculation Unit ( FIG. 30 )&gt; 
     By the present calculation unit, then ignition timing correction value (Adv_hos) is calculated which is specifically shown in  FIG. 30 .
     When fp_cont 2 =0, Adv_hos is made 0.   When fp_cont 2 =1, Adv_hos is increased stepwise by K 1 _Adv until ind_ita≧K 1 _ita is achieved.   

     As shown in  FIG. 17 , K 1 _ita is made an energy efficiency index corresponding to a target HC discharged quantity. Further, it may be changed also based on the operation condition of the engine. It may be changed also based on a change (deterioration) of the light-off performance of the catalyst. More specifically, K 1 _ita is reduced according to deterioration of the light-off performance of the catalyst. 
     Example 3 
     In example 2, the engine was controlled so that the HC discharged quantity at the time of start became a predetermined value from the efficiency of the engine and the stability of the engine. In example 3, with respect to example 2, when the ignition timing is retarded, if the stability of the engine deteriorates to a predetermined value or more, even if the efficiency of the engine has not reached a target value, retarding of the ignition timing is stopped, and the ignition timing is advanced so as to secure stability. Further, diagnosis of the HC discharged quantity at the time of start is also executed in parallel. 
       FIG. 18  is a system drawing showing the present example and is similar to that of example 1, and therefore detailed description thereof will be omitted.  FIG. 19  shows the inside of the control unit  16  and is similar to example 1, and therefore detailed description thereof will be also omitted. Below, a control program written in the ROM  22  in  FIG. 19  will be described.  FIG. 31  is a block diagram expressing the total control, and is formed of calculation units described below.
     Basic fuel injection quantity calculation unit ( FIG. 26 )   Control permit unit  1  ( FIG. 27 )   Instability index calculation unit ( FIG. 23 )   Basic fuel injection quantity correction value calculation unit ( FIG. 28 )   Control permit unit  2  ( FIG. 29 )   Efficiency index calculation unit ( FIG. 22 )   Ignition timing correction value calculation unit ( FIG. 32 )   Diagnosis permit unit ( FIG. 21 )   Abnormality determination unit ( FIG. 24 )   

     By “the basic fuel injection quantity calculation unit”, a basic fuel injection quantity Tp 0  is calculated. By “the control permit unit  1 ”, a flag (fp_cont 1 ) is calculated which permits control for making the air fuel ratio lean based on the instability index (Ind_sta) after start. By “the instability index calculation unit”, the instability index (Ind_sta) is calculated which is a variation degree of the angular acceleration meaning instability of combustion. By “the basic fuel injection quantity correction value calculation unit”, a basic fuel injection quantity correction value (F_hos) for making the air fuel ratio lean is calculated. By “the control permit unit  2 ”, a flag (fp_cont 2 ) is calculated which permits control for retarding ignition timing based on the efficiency index (Ind_ita) after the air fuel ratio is made lean. By “the efficiency index calculation unit”, the engine efficiency index (Ind_ita) is calculated which is a ratio of the engine speed (Ne) and the suction air quantity (Qa). By “the ignition timing correction value calculation unit”, an ignition timing correction value (Adv_hos) retarding the ignition timing is calculated. By “the diagnosis permit unit”, a flag (fp_diag) permitting diagnosis is calculated. By “the abnormality determination unit”, whether or not the HC discharged quantity at the time of start is a predetermined value or less is determined from both values of the efficiency index (Ind_ita) and the instability index (Ind_sta), and, when the HC discharged quantity at the time of start is a predetermined value or more, an abnormality flag (f_MIL) is made 1. Below, the detail of respective calculation units will be described. 
     &lt;Basic Fuel Injection Quantity Calculation Unit ( FIG. 26 )&gt; 
     By the present calculation unit, the basic fuel injection quantity (Tp 0 ) is calculated which is specifically shown in  FIG. 26 , however, because it is same with that of example 2, detail description thereof will be omitted. 
     &lt;Control Permit Unit  1  ( FIG. 27 )&gt; 
     By the present calculation unit, the control permit flag  1  (fp_cont 1 ) is calculated which is specifically shown in  FIG. 27 , however, because it is same with that of example 2, detail description thereof will be omitted. 
     &lt;Instability Index Calculation Unit ( FIG. 23 )&gt; 
     By the present calculation unit, the instability index (Ind_sta) is calculated which is specifically shown in  FIG. 23 , however, because it is same with that of example 1, detail description thereof will be omitted. 
     &lt;Basic Fuel Injection Quantity Correction Value Calculation Unit ( FIG. 28 ). 
     By the present calculation unit, the basic fuel injection quantity correction value (F_hos) is calculated which is specifically shown in  FIG. 28 , however, because it is same with that of example 2, detail description thereof will be omitted. 
     &lt;Control Permit Unit  2  ( FIG. 29 )&gt; 
     By the present calculation unit, the control permit flag  2  (fp_cont 2 ) is calculated which is specifically shown in  FIG. 29 , however, because it is same with that of example 2, detail description thereof will be omitted. 
     &lt;Instability Index Calculation Unit ( FIG. 22 )&gt; 
     By the present calculation unit, the efficiency index (Ind_ita) is calculated which is specifically shown in  FIG. 22 , however, because it is same with that of example 1, detail description thereof will be omitted. 
     &lt;Ignition Timing Correction Value Calculation Unit ( FIG. 32 )&gt; 
     By the present calculation unit, the ignition timing correction value (Adv_hos) is calculated which is specifically shown in  FIG. 32 .
     When fp_cont 2 =0, Adv_hos is made 0.   When fp_cont 2 =1, if ind_sta≦K 1 _sta, Adv_hos is increased by K 1 _Adv stepwise until ind_ita≦K 1 _ita is achieved.   

     When ind_sta&gt;K 1 _sta, Adv_hos is reduced by K 2 _Adv stepwise until ind_sta≦K 1 _sta is achieved. 
     As shown in  FIG. 17 , K 1 _ita is made an instability index value corresponding to a target HC discharged quantity. Further, it may be changed also based on the operation condition of the engine. It may be changed also based on a change (deterioration) of the light-off performance of the catalyst. More specifically, K 1 _ita is reduced according to deterioration of the light-off performance of the catalyst. 
     K 1 _Adv and K 2 _Adv are values that determine a retarding speed and an advance speed respectively, and are determined taking responsiveness of the engine and the like into account. 
     &lt;Diagnosis Permit Unit ( FIG. 21 )&gt; 
     By the present calculation unit, the diagnosis permit flag (fp_diag) is calculated which is specifically shown in  FIG. 21 , however, because it is same with that of example 1, detail description thereof will be omitted. 
     &lt;Abnormality Determination Unit ( FIG. 24 )&gt; 
     By the present calculation unit, the abnormality flag (f_MIL) is calculated which is specifically shown in  FIG. 24 , however, because it is same with that of example 1, detail description thereof will be omitted. 
     LIST OF REFERENCE SIGNS 
     
         
           1  . . . air cleaner 
           2  . . . air flow sensor 
           3  . . . electronic throttle 
           4  . . . intake manifold 
           5  . . . collector 
           6  . . . accelerator 
           7  . . . fuel injection valve 
           8  . . . ignition plug 
           9  . . . engine 
           10  . . . exhaust manifold 
           11  . . . three way catalyst 
           12  . . . catalyst upstream air fuel ratio sensor 
           13  . . . accelerator valve opening sensor 
           14  . . . water temperature sensor 
           15  . . . engine speed sensor 
           16  . . . control unit 
           17  . . . throttle valve opening sensor 
           18  . . . exhaust gas circulation pipe 
           19  . . . exhaust gas circulation quantity adjust valve 
           20  . . . catalyst downstream O 2  sensor 
           21  . . . CPU mounted inside control unit 
           22  . . . ROM mounted inside control unit 
           23  . . . RAM mounted inside control unit 
           24  . . . input circuit of various kinds of sensors mounted inside control unit 
           25  . . . port inputting various kinds of sensor signals and outputting actuator motion signal 
           26  . . . ignition output circuit outputting drive signal to ignition plug at appropriate timing 
           27  . . . fuel injection valve drive circuit outputting appropriate pulse to fuel injection valve 
           28  . . . electronic throttle drive circuit 
           29  . . . intake temperature sensor