Patent Publication Number: US-11378051-B2

Title: Ignition control device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation application of International Application No. PCT/JP2020/007586 filed on Feb. 26, 2020 which designated the U.S. and claims priority to Japanese Patent Application No. 2019-073861 filed on Apr. 9, 2019, the contents of each of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     Technical Field 
     The present invention relates to an ignition control device for controlling ignition of an internal combustion engine or the like. 
     Related Art 
     An ignition control device for a spark-ignition vehicle engine includes an ignition device in which a spark plug is provided for each cylinder and each spark plug is connected to an ignition coil having a primary coil and a secondary coil. The high voltage generated in the secondary coil when the energization of the primary coil is interrupted is applied to generate a spark discharge. Further, in order to facilitate ignition of the air-fuel mixture by the spark discharge, a means for supplying discharge energy after starting the spark discharge is provided. 
     Although it is possible to perform ignition multiple times by repeating the ignition operation by one ignition coil to achieve this, in order to perform more stable ignition control, discharge energy may be added while the spark discharge is being generated by the main ignition operation so that the secondary current is increased in a superimposed manner. In a known ignition device, two systems of energy supply means are provided for each cylinder. After starting the main ignition using the energy supply means of one of the systems, the energy supply means of the other system is operated to continuously supply a secondary current in the same direction through the secondary coil so that the spark discharge continues. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings: 
         FIG. 1  is a circuit configuration diagram of an ignition control device according to the first embodiment; 
         FIG. 2  is a waveform diagram of an ignition control signal received by the ignition control device according to the first embodiment; 
         FIG. 3  is a circuit configuration diagram of a signal separation circuit unit forming a part of an ignition device of the ignition control device according to the first embodiment; 
         FIG. 4  is a timing chart diagram showing the relationship between the ignition control signal and the gate signals for main ignition and energy input according to the first embodiment; 
         FIG. 5  is a timing chart diagram showing the processes of the main ignition operation and the energy input operation based on signals generated in the ignition control device according to the first embodiment; 
         FIG. 6  is a circuit configuration diagram of a waveform shaping circuit forming a part of the ignition device according to the to the first embodiment; 
         FIG. 7  is a timing chart diagram showing the relationship between the ignition control signal and the various signals generated in the waveform shaping circuit according to the first embodiment; 
         FIG. 8  is a circuit configuration diagram of an IGT generation circuit forming a part of the ignition device according to the first embodiment; 
         FIG. 9  is a time chart diagram showing the relationship between the ignition control signal and the various signals generated in the IGT generation circuit according to the first embodiment; 
         FIG. 10  is a circuit configuration diagram of an IGW generation circuit forming a part of the ignition device according to the first embodiment; 
         FIG. 11  is a timing chart diagram showing the relationship between the ignition control signal and the various signals generated in the IGW generation circuit according to the first embodiment; 
         FIG. 12  is a timing chart diagram showing the relationship between the signals generated in the IGA generation circuit forming a part of the ignition device and the energy input operation according to the first embodiment; 
         FIG. 13  is a circuit configuration diagram of a reset circuit forming a part of the waveform shaping circuit according to the first embodiment; 
         FIG. 14  is a timing chart diagram showing the relationship between the reset signal and various signals generated in the reset circuit according to the first embodiment; 
         FIG. 15  is a timing chart diagram showing the relationship between the ignition control signal and the various signals generated in the signal separation circuit unit, and the processes of the main ignition operation and the energy input operation according to the second embodiment; 
         FIG. 16  is a timing chart diagram showing the relationship between the ignition control signal, the various signals generated in the signal separation circuit unit, and the waiting time according to the third embodiment; 
         FIG. 17  is a timing chart diagram comparing the relationship between the ignition control signal and the various signals generated in the signal separation circuit unit under a certain waiting time, and their relationship under another waiting time set based on the engine operating condition according to the fourth embodiment; 
         FIG. 18  is a diagram showing the relationship between the engine operating condition and the waiting time set in the signal separation circuit unit according to the fourth embodiment; 
         FIG. 19  is a flowchart showing the processes of the main ignition operation and the energy input operation carried out by the ignition control device according to the fifth embodiment; 
         FIG. 20  is a flowchart comparing the processes of the main ignition operation and the energy input operation based on  FIG. 19  according to the fifth embodiment between the first to third embodiments; 
         FIG. 21  is a timing chart diagram showing examples of the main ignition operation and the energy input operation carried out by the ignition control device according to the fifth embodiment in the case of the first embodiment; 
         FIG. 22  is a circuit configuration diagram of an IGT generation circuit forming a part of the ignition device according to the sixth embodiment; 
         FIG. 23  is a timing chart diagram showing the relationship between the ignition control signal and the various signals generated in the IGT generation circuit according to the sixth embodiment; 
         FIG. 24  is a circuit configuration diagram of the IGT generation circuit forming a part of the ignition device according to the sixth embodiment; 
         FIG. 25  is a timing chart diagram showing the relationship between the ignition control signal and the various signals generated in the IGT generation circuit according to the sixth embodiment; 
         FIG. 26  is a circuit configuration diagram of the IGW generation circuit forming a part of the ignition device according to the sixth embodiment; 
         FIG. 27  is a timing chart diagram showing the relationship between the ignition control signal and the various signals generated in the IGW generation circuit according to the sixth embodiment; 
         FIG. 28  is a timing chart diagram showing the relationship between the signals generated in the IGA generation circuit forming a part of the ignition device and various signals according to the sixth embodiment; 
         FIG. 29  is a timing chart diagram showing the relationship between the signals generated in the IGA generation circuit forming a part of the ignition device and various signals according to the sixth embodiment; and 
         FIG. 30  is a circuit configuration diagram of an ignition control device according to the seventh embodiment. 
     
    
    
     DESCRIPTION OF SPECIFIC EMBODIMENTS 
     The known ignition device, as disclosed in JP A-2017-210965, has two systems of energy supply means, the main ignition circuit and the energy input circuit, and a shared signal line is provided in one of the systems in order to prevent problems such as insufficient number of output terminals on the control side. One end of the shared signal line is connected to an output terminal on the control side, and the other end is branched in the middle. Each of the branches is connected to an energy input circuit provided for each cylinder. This configuration makes it possible to control the energy input of a plurality of cylinders by adding one signal line. 
     The configuration of the ignition device disclosed in JP A-2017-210965 includes a branch connector and a branch line for each cylinder for branching the shared signal line therein. Therefore, as the number of cylinders increases, the wiring becomes complicated, which makes it necessary to increase the size of the branching part in order to ensure the reliability of the branching part, resulting in an increased size. Further, since a plurality of signals for at least main ignition and energy input are transmitted, noise and the like may be generated by inputting signals during the ignition operation, and it may be necessary to take measures such as applying a noise filter to avoid its influence. 
     Therefore, it is desired to simplify the system configuration by further integrating the signal lines connecting the devices to reduce the number of connector terminals and connection ports, and reducing the effects such as that of signal transmission on the ignition operation to eliminate the need for means such as a noise filter. 
     In view of the foregoing, it is desired to have a compact and high-performance ignition control device capable of transmitting and receiving signals for performing the main ignition operation and the energy input operation using fewer signal lines. 
     One aspect of the present disclosure provides an ignition control device including: an ignition coil which generates discharge energy in a secondary coil connected to a spark plug by increasing and decreasing a primary current flowing through a primary coil; a main ignition circuit unit which controls energization of the primary coil to perform a main ignition operation for causing the spark plug to generate a spark discharge; and an energy input circuit unit which performs an energy input operation for superimposing a current of the same polarity on a secondary current caused to flow through the secondary coil by the main ignition operation. In the ignition control device, the ignition control device further comprises a signal separation circuit unit which receives an ignition control signal which is a signal combining a main ignition signal for controlling the main ignition operation, an energy input signal for controlling the energy input operation, and a target secondary current instruction signal, and separates one or more signals included in the received ignition control signal. The signal separation circuit unit generates the main ignition signal such that a point in time when a waiting time has passed from when a signal level of the ignition control signal changed from a first level to a second level for the first time, and the signal level of the ignition control signal is the second level, is a start of the main ignition signal, and a point in time at which the signal level of the ignition control signal shifts to the first level thereafter is an end of the main ignition signal. The main ignition circuit unit energizes the primary coil at the start of the main ignition signal and cuts off the energization of the primary coil at the end of the main ignition signal. 
     The ignition control signal received by the signal separation circuit unit of the ignition control device includes information for three signals, namely, the main ignition signal, the energy input signal, and the target secondary current instruction signal, and it can be separated into the individual signals based on the signal waveform. For example, the main ignition signal is generated with a start condition that the signal level is the second level when a predetermined waiting time has passed after the signal level first changes from the first level to the second level, and an end condition that the signal level shift to the first level thereafter. The main ignition circuit unit performs an operation for energizing the primary coil based on the generated main ignition signal, and performs the main ignition operation. In case the energy input operation is to be performed following the main ignition operation, the energy input signal and the target secondary current instruction signal are also generated by being separated in the signal separation circuit unit. 
     Since a plurality of signals for main ignition and energy input can be combined into one ignition control signal and transmitted on one signal line, there is no need to provide a plurality of signal lines for each cylinder, or branch a shared line. Further, since the signal for the energy input operation can be transmitted before the start of the main ignition operation, the energization operation for the main ignition is less likely to be affected by noise. Therefore, efficient ignition control can be achieved with reduced numbers of wires, connectors, and connection ports and without complicating the system configuration or increasing the size. 
     Thus, according to the above-described aspect, it is possible to provide a compact and high-performance ignition control device capable of transmitting and receiving signals for performing the main ignition operation and the energy input operation using fewer signal lines. 
     First Embodiment 
     A first embodiment according to the ignition control device will be described with reference to  FIGS. 1 to 14 . 
     In  FIG. 1 , the ignition control device  1  is applied to, for example, an internal combustion engine such as a vehicle spark-ignition engine to control the ignition of the spark plugs P which are each attached to a corresponding cylinder. The ignition control device  1  includes an ignition device  10  provided with an ignition coil  2 , a main ignition circuit unit  3 , an energy input circuit unit  4 , and a signal separation circuit unit  5 , and an engine electronic control device (hereinafter, abbreviated as engine ECU; Electronic Control Unit)  100  as an ignition control signal transmission unit configured to give ignition instructions to the ignition device  10   
     The ignition coil  2  generates discharge energy in the secondary coil  22  connected to the spark plug P by increasing and decreasing the primary current I 1  flowing through the primary coil  21 . The main ignition circuit unit  3  controls the energization of the primary coil  21  of the ignition coil  2  to perform a main ignition operation for causing the spark plug P to generate a spark discharge. The energy input circuit unit  4  performs an energy input operation for superimposing a current of the same polarity on the secondary current I 2  flowing through the secondary coil  22  by the main ignition operation. 
     The primary coil  21  includes, for example, a main primary coil  21   a  and an auxiliary primary coil  21   b , and the energy input circuit unit  4  can control the energy input operation by controlling the energization of the auxiliary primary coil  21   b.    
     The signal separation circuit unit  5  receives an ignition control signal IG from the engine ECU  100  and separates a signal included in the ignition control signal IG. The ignition control signal IG is a signal combining a main ignition signal IGT for controlling the main ignition operation, an energy input signal IGW for controlling the energy input operation, and a target secondary current instruction signal IGA, and is received as, for example, one pulse signal or a combination of two signals. The ignition control signal IG is separated into individual signals again in the signal separation circuit unit  5 . For example, the main ignition signal IGT is generated by separating it from the ignition control signal to enable the main ignition operation. 
     At this time, the signal separation circuit unit  5  generates the main ignition signal IGT based on the signal level of the ignition control signal IG. Specifically, as shown in  FIG. 2 , when a waiting time t wait  has passed from when the signal level changed from the first level (for example, the L level) to the second level (for example, the H level) for the first time, and the signal level of the ignition control signal IG is the second level (for example, the H level), that point in time is the start of the main ignition signal IGT, and when the signal level of the ignition control signal IG reaches the first level (for example, the L level) after that, that point in time is the end of the main ignition signal IGT. 
     The waiting time t wait  is a preset time for generating the main ignition signal IGT from the ignition control signal IG, and as will be described later, it corresponds to the time period from the switching (for example, rising) of the signal level of the ignition control signal IG to the switching (for example, rising) of the signal level of the main ignition signal IGT. 
     In accordance with this, the main ignition operation is performed in the main ignition circuit unit  3  in which the primary coil  21  is energized at the start of the main ignition signal IGT and the energization of the primary coil  21  is cut off at the end of the main ignition signal IGT. Note that the signal level of the ignition control signal IG is represented by two voltage levels, the H level and L level. When the voltage is equal to or higher than a preset threshold voltage, the level becomes the H level, and when it is below the threshold voltage, the level becomes the L level. In the present embodiment, it will be assumed below that the first level corresponds to the L level and the second level corresponds to the H level. 
     In the present embodiment, the ignition control signal IG is generated as a signal composed of a first pulse signal IG 1  and a second pulse signal IG 2 . The engine ECU  100  generates an ignition control signal IG that combines these two signals IG 1  and IG 2  every combustion cycle (for example, 720° CA) and transmits it to the signal separation circuit unit  5  prior to the main ignition operation. 
     The first signal IG 1  and the second signal IG 2  of the ignition control signal IG are distinguished from each other by, for example, assuming that the first input signal input from the engine ECU  100  to the ignition device  10  after the operation of the ignition control device  1  has been started is the first signal IG 1 , and the next input signal is the second signal IG 2 . The subsequent input signals can also be identified by performing the same operation repeatedly. 
     In that case, as shown in  FIG. 3 , the signal separation circuit unit  5  includes circuits for receiving the ignition control signal IG and separating the received ignition control signal IG into 3 signals included in the ignition control signal IG. 
     Specifically, as shown in  FIG. 4 , it includes a main ignition signal generation circuit (hereinafter, referred to as an IGT generation circuit)  52  which, when the waiting time t wait  has elapsed from the detection start time (that is, rising) of the first signal IG 1 , and the signal level of the second signal IG 2  is the second level (that is, the H level), starts generating the main ignition signal IGT at that time and terminates it at the detection end time (that is, falling) of the second signal IG 2 . The IGT generation circuit  52  may include a circuit for generating the waiting time t wait . 
     Further, the signal separation circuit unit  5  generates the energy input signal IGW based on the pulse waveform information of the first signal IG 1  and the second signal IG 2 , and the target secondary current instruction signal IGA can be generated based on the pulse waveform information of the first signal IG 1 . The pulse waveform information is information such as the time period or interval determined based on the rising or falling of one or more pulses, and it includes the time period of the rising or falling of a pulse, an interval between the rising or falling of a pulse and the rising or falling of another pulse, and the like. 
     In this embodiment, for example, an energy input signal generation circuit (hereinafter, referred to as an IGW generation circuit)  53  is provided which generates the energy input signal IGW based on the rising interval t IGW_IN  as a detection interval between the first signal IG 1  and the second signal IG 2 . Further, a target secondary current instruction signal generation circuit (hereinafter referred to as an IGA generation circuit)  54  may be provided which generates the target secondary current instruction signal IGA based on the rising period t IGA_IN  as a detection period of the first signal IG 1 . 
     The ignition control device  1  operates the main ignition circuit unit  3  based on the main ignition signal IGT to perform the main ignition operation. Further, after the main ignition, it operates the energy input circuit unit  4  based on the energy input signal IGW to perform the energy input operation and make the spark discharge continue. The energy input for this continuous discharge is indicated by the target secondary current instruction signal IGA. The ignition control device  1  further includes a feedback control unit  6  configured to feedback-control the secondary current I 2 . The feedback control unit  6  feedback-controls the secondary current I 2  flowing through the secondary coil  22  of the ignition coil  2  based on the target secondary current instruction signal IGA so that it reaches the target secondary current value I 2   tgt.    
     Next, the configuration of the ignition control device  1  will be described in detail. 
     The engine to which the ignition control device  1  of the present embodiment is applied is, for example, a 4-cylinder engine. A spark plugs P is for provided each cylinder (for example, represented by P # 1  to P # 4  in  FIG. 1 ), and an ignition device  10  is provided for each spark plug P. The ignition control signal IG is transmitted from the engine ECU  100  to each ignition device  10 . 
     Each spark plug P has a known configuration including a center electrode P 1  and a ground electrode P 2  facing each other, and the space formed between the leading ends of the two electrodes serves as a spark gap G. The discharge energy generated in the ignition coil  2  based on the ignition control signal IG is supplied to the spark plug P so that a spark discharge is generated in the spark gap G, which ignites the air-fuel mixture in the engine combustion chamber (not shown). The energization of the ignition coil  2  is controlled based on the main ignition signal IGT, the energy input signal IGW, and the target secondary current instruction signal IGA included in the ignition control signal IG. 
     In the ignition coil  2 , the main primary coil  21   a  or the auxiliary primary coil  21   b  serving as the primary coil  21  and the secondary coil  22  are magnetically coupled to each other to form a known step-up transformer. One end of the secondary coil  22  is connected to the center electrode P 1  of the spark plug P, and the other end is grounded via a first diode  221  and a secondary current detection resistor R 1 . The first diode  221  is placed so that its anode terminal is connected to the secondary coil  22  and its cathode terminal is connected to the secondary current detection resistor R 1  so as to regulate the direction of the secondary current I 2  flowing through the secondary coil  22 . The secondary current detection resistor R 1  constitutes a feedback control unit  6  together with a secondary current feedback circuit (for example, represented by I 2 F/B in  FIG. 1 )  61 , which will be described in detail later. 
     The main primary coil  21   a  and the auxiliary primary coil  21   b  are connected in series with each other and are connected in parallel to a DC power source B such as a vehicle battery. Specifically, an intermediate tap  23  is provided between one end of the main primary coil  21   a  and one end of the auxiliary primary coil  21   b , and a power supply line L 1  leading to the DC power source B is connected to the intermediate tap  23 . The other end of the main primary coil  21   a  is grounded via a switching element for main ignition (hereinafter, abbreviated as main ignition switch) SW 1 , and the other end of the auxiliary primary coil  21   b  is grounded via a switching element for making the discharge continue (hereinafter, abbreviated as discharge continuation switch) SW 2 . 
     Thus, the battery voltage can be applied to the primary coil  21   a  or the auxiliary primary coil  21   b  when the main ignition switch SW 1  or the discharge continuation switch SW 2  is on. The main ignition switch SW 1  is a part of the main ignition circuit unit  3 , and the discharge continuation switch SW 2  is a part of the energy input circuit unit  4 . 
     The ignition coil  2  is integrally formed by winding the primary coil  21  and the secondary coil  22  around, for example, a bobbin for the primary coil and a bobbin for the secondary coil placed around a core  24 . By having a sufficiently large turn ratio, which is the ratio of the number of turns of the main primary coil  21   a  or the auxiliary primary coil  21   b , which is the primary coil  21 , to the number of turns of the secondary coil  22 , a high voltage corresponding to the turn ratio can be generated in the secondary coil  22 . The main primary coil  21   a  and the auxiliary primary coil  21   b  are wound so that the directions of the magnetic flux they generate when energized by the DC power source B are opposite to each other, and the number of turns of the auxiliary primary coil  21   b  is smaller than that of the main primary coil  21   a.    
     As a result, after generating a discharge in the spark gap G of the spark plug P by the voltage generated by interrupting the energization of the main primary coil  21   a , a superimposed magnetic flux having the same direction can be generated by energizing the auxiliary primary coil  21   b  which increases the discharge energy in a superimposed manner. 
     The main ignition circuit unit  3  includes the main ignition switch SW 1  and a switch drive circuit for main ignition operation  31  configured to drive the main ignition switch SW 1  on and off (hereinafter, referred to as a main ignition drive circuit). The main ignition switch SW 1  is a voltage-driven switching element, for example, an IGBT (that is, an insulated gate bipolar transistor). The conduction between the collector terminal and the emitter terminal is established or cut off by controlling the gate potential through a gate signal IGBT_gate input to the gate terminal. The collector terminal of the main ignition switch SW 1  is connected to the other end of the main primary coil  21   a , and its emitter terminal is grounded. 
     The main ignition signal IGT output from the signal separation circuit unit  5  is input to the input terminal of the main ignition drive circuit  31  via an output signal line L 2 . The main ignition drive circuit  31  drives the main ignition switch SW 1  in response to the main ignition signal IGT. 
     The main ignition drive circuit  31  (see, for example,  FIG. 4 ) generates a gate signal IGBT_gate corresponding to the main ignition signal IGT to turn the main ignition switch SW 1  on or off at a certain timing. 
     Specifically (see, for example,  FIG. 5 ), when the main ignition switch SW 1  is turned on at the time the main ignition signal IGT rises, energization of the main primary coil  21   a  is started and the primary current I 1  flows. Next, when the main ignition switch SW 1  is turned off at the time the main ignition signal IGT falls, the energization of the main primary coil  21   a  is cut off, and a high voltage is generated in the secondary coil  22  by mutual induction. This high voltage is applied to the spark gap G of the spark plug P to generate a spark discharge, and the secondary current I 2  flows. 
     The rising period t IGT  (that is, the period from the rising to falling) of the main ignition signal IGT is appropriately set, for example, so that the primary current I 1  has a predetermined value when the energization of the primary coil  21  is cut off. 
     The energy input circuit unit  4  includes the discharge continuation switch SW 2  and a auxiliary primary coil control circuit  41  that outputs a drive signal for driving the discharge continuation switch SW 2  on and off to control energization of the auxiliary primary coil  21   b . Further, a switching element (hereinafter, abbreviated as a flyback switch) SW 3  is provided to open and close a flyback path L 11  connected to the auxiliary primary coil  21   b . The on/off operation is carried out by a drive signal from the auxiliary primary coil control circuit  41 . 
     The discharge continuation switch SW 2  and the flyback switch SW 3  are voltage-driven switching elements, for example, MOSFETs (that is, field effect transistors). The conduction between the drain terminal and the source terminal is established or cut off by controlling the gate potential through a gate signal MOS_gate 1 , MOS_gate 2  input to the gate terminal. The drain terminal of the discharge continuation switch SW 2  is connected to the other end of the auxiliary primary coil  21   b , and its source terminal is grounded. 
     The flyback path L 11  is provided between the other end of the auxiliary primary coil  21   b  (that is, the side opposite to the main primary coil  21   a ) and the power supply line L 1 . The drain terminal of the flyback switch SW 3  is connected to the connection point between the other end of the auxiliary primary coil  21   b  and the discharge continuation switch SW 2 , and its source terminal is connected to the power supply line L 1  via the second diode  11 . Further, in the power supply line L 1 , a third diode  12  is provided between its connection point with the flyback path L 11  and the DC power source B. The forward direction of the second diode  11  is the direction toward the power supply line L 1 , and the forward direction of the third diode  12  is the direction toward the primary coil  21 . 
     The energy input signal IGW and the target secondary current instruction signal IGA output from the signal separation circuit unit  5  are input to the input terminal of the auxiliary primary coil control circuit  41  via output signal lines L 3 , L 4 . Further, a feedback signal SFB is input to the auxiliary primary coil control circuit  41  from the secondary current feedback circuit  61  of the feedback control unit  6 , and further, a battery voltage signal SB is input from the power supply line L 1 . 
     The auxiliary primary coil control circuit  41  (see, for example,  FIG. 4 ) generates gate signals MOS_gate 1 , MOS_gate 2  to drive the discharge continuation switch SW 2  and the flyback switch SW 3 . The gate signal MOS_gate 2  will be ON for the energy input period t IGW  indicated by the energy input signal IGW, and the gate signal MOS_gate 1  will be driven on and off to maintain the target secondary current value I 2   tgt  indicated by the target secondary current instruction signal IGA (see, for example,  FIG. 5 ). 
     The secondary current feedback circuit  61  outputs, for example, the detected value of the secondary current I 2  based on the secondary current detection resistor R 1  as the feedback signal SFB, and the auxiliary primary coil control circuit  41  drives the discharge continuation switch SW 2  and the flyback switch SW 3  based on the result of comparison between the detected value of the secondary current I 2  and the target secondary current value I 2   tgt . At this time, it may also be determined whether the energy input operation is possible based on the battery voltage signal SB. 
     Specifically, when the energy input signal IGW rises after a predetermined delay period t fil  from the falling of the main ignition signal IGT, the gate signal MOS_gate 2  rises and the flyback switch SW 3  is turned on. Next, when the secondary current I 2  (absolute value) flowing through the secondary coil  22  due to the main ignition operation decreases and reaches the target secondary current value I 2   tgt , the gate signal MOS_gate 1  rises and the discharge continuation switch SW 2  is turned on. As a result, energization of the auxiliary primary coil  21   b  starts, and the current I NET  flowing through the secondary primary coil  21   b  causes superimposition of the secondary current I 2 . 
     The target secondary current value I 2   tgt  serves as a lower limit threshold (absolute value) for turning on the discharge continuation switch SW 2 , and it is indicated by the target secondary current instruction signal IGA. The target secondary current instruction signal IGA is a function f(t IGA_IN ) based on the rising period t IGA_IN  of the first signal IG 1 , and this function is set before starting the main ignition operation. An upper limit threshold (absolute value) for turning off the discharge continuation switch SW 2  is set corresponding to the lower limit threshold. Thus, when the secondary current I 2  (absolute value) increases again due to the energy supply and reaches the predetermined upper limit threshold, the gate signal MOS_gate 1  rises and the discharge continuation switch SW 2  is turned off. In this way, the discharge continuation switch SW 2  is repeatedly turned on and off according to the gate signal MOS_gate 1 , so that the secondary current I 2  can be maintained near the target secondary current value I 2   tgt.    
     Since the flyback switch SW 3  is turned on while the discharge continuation switch SW 2  is off, the other end of the auxiliary primary coil  21   b  and the power supply line L 1  are connected via the flyback path L 11 . Therefore, a flyback current flows when the energization of the secondary primary coil  21   b  is cut off, and the current of the auxiliary primary coil  21   b  changes slowly, so that a sudden decrease in the secondary current I 2  can be suppressed. 
     The predetermined delay period t fil  is appropriately set so that, for example, the energy input operation is performed after the secondary current I 2  caused to flow by the main ignition operation has dropped to some extent. This is for outputting the energy input signal IGW, which indicates the period for which the energy input operation should be carried out, at a certain timing after the spark discharge has been started by the main ignition operation, which makes it possible to effectively maintain the spark discharge by the energy input. 
     Next, the details of the signal separation circuit unit  5  will be described with reference to  FIGS. 2 to 5 . 
     As shown in  FIG. 2 , the ignition control signal IG includes the first signal IG 1  and the second signal IG 2 . The earlier signal output when the ignition control signal IG rises is the first signal IG 1 , and the latter signal output after the first signal IG 1  has fallen is the second signal IG 2 . 
     The ignition control signal IG sets the energy input period t IGW  by the rising interval t IGW_IN , which is the length from the rise of the first signal IG 1  to the rise of the second signal IG 2 . Further, it sets the target secondary current value I 2   tgt  by the rising period t IGA_IN , which is the length from the rising to falling of the first signal IG 1 . 
     Note that the period from the rise to the fall of the ignition control signal IG is the period from the rise of the first signal IG 1  to the fall of the second signal IG 2 , and the length of this period is the sum of the length of the waiting time t wait  and the length of the rising period t IGT  of the main ignition signal IGT. In other words, the ignition control signal IG is output at a timing earlier than the rising of the main ignition signal IGT by the waiting time t wait . The ignition control signal IG and the main ignition signal IGT fall at the same time, and no signal is transmitted from the engine ECU  100  after that. 
     In  FIG. 3 , the signal separation circuit unit  5  includes a waveform shaping circuit  51  for shaping the waveform of the ignition control signal IG, an IGT generation circuit  52  for generating the main ignition signal IGT, an IGW generation circuit  53  for generating the energy input signal IGW, and an IGA generation circuit  54  for generating the target secondary current instruction signal IGA. Further, a reset signal generation circuit  55  for generating a reset signal RES is provided. 
     As shown in  FIGS. 4 and 5 , the ignition control signal IG is a composite signal obtained by combining the main ignition signal IGT, the energy input signal IGW, and the target secondary current instruction signal IGA. First, filtering is performed on the ignition control signal IG in the waveform shaping circuit  51  shown in  FIG. 3 . As a result, it is output to the IGT generation circuit  52  and the reset signal generation circuit  55  as a square wave signal  1   a  including the first signal IG 1  and the second signal IG 2  each having a square waveform from which noise has been removed. The reset signal RES from the reset signal generation circuit  55  is output to the IGT generation circuit  52 , the IGW generation circuit  53 , and the IGA generation circuit  54 . 
     Further, based on the square wave signal  1   a , a signal IGT_DCT for generating the main ignition signal IGT, a signal IGW_DCT for generating the energy input signal IGW, and a signal IGT_DCT for generating the target secondary current instruction signal IGA are generated. These signals IGT_DCT, IGW_DCT, and IGA_DCT are output to the IGT generation circuit  52 , the IGW generation circuit  53 , and the IGA generation circuit  54 , respectively. 
     Next, the configurations of the waveform shaping circuit  51 , the IGT generation circuit  52 , the IGW generation circuit  53 , and the IGA generation circuit  54 , which constitute the signal separation circuit unit  5 , will be described with reference to  FIGS. 6 to 13 . 
     As shown in  FIG. 6 , the waveform shaping circuit  51  includes a first comparator  511 , a low-pass filter  512 , first to third D flip-flops  513   a  to  513   c , first to fourth AND circuits  514   a  to  514   d , and first to third inverter circuits  515   a  to  515   c.    
     A reference potential Vth 1  serving as a threshold is applied to the negative input terminal of the first comparator  511 , and when the ignition control signal IG is input to its positive input terminal, an output signal based on the result of comparison between the two is transmitted from the output terminal to the low-pass filter  512 . The low-pass filter  512  has a known filter configuration including a resistor R 1  and a capacitor C 1 . 
     Thus, as shown in  FIG. 7 , the first comparator  511  amplifies or reduces the output according to the comparison result between the ignition control signal IG and the reference potential Vth 1 , and shapes the signal into an H/L binary signal. By removing the high-frequency noise by passing the signal through the low-pass filter  512 , the ignition control signal IG is shaped into a square waveform having rising and falling edges (that is, the square wave signal  1   a  in the figure). 
     The shaped square wave signal  1   a  is input to the first D flip-flop  513   a . The first D flip-flop  513   a  is a circuit for detecting the first rise of the ignition control signal IG and outputting it as the signal IGT_DCT. The square wave signal  1   a  is input to the clock terminal (hereinafter referred to as CLK terminal) of the first D flip-flop  513   a , and a power supply is connected to the data terminal (hereinafter referred to as D terminal) and a potential corresponding to the H level is supplied. Thus, when the signal level of the D terminal is latched in synchronization with the rise of the square wave signal  1   a , the signal IGT_DCT output from the output terminal (hereinafter referred to as the Q terminal) rises to the H level. 
     Note that a reset signal RES from the reset signal generation circuit  55  is input to the reset terminal (hereinafter referred to as the RES terminal) of the first D flip-flop  513   a , and the latch is reset when the reset signal RES switches from the H level to the L level. 
     As shown in  FIG. 7 , the reset signal RES switches from the H level to L level when a predetermined reset period t reswait  passes after the second fall of the square wave signal  1   a  (that is, corresponding to the fall of the second signal IG 2 ). Accordingly, every time the ignition control signal IG is output, the signal IGT_DCT, which is a detection signal of the rise of the ignition control signal IG (that is, the rise of the first signal IG 1 ), is output from the first D flip-flop  513   a , and it is reset when the signal RES falls. 
     The second D flip-flop  513   b  has a configuration equivalent to that of the first D flip-flop  513   a , and it is a circuit for detecting the second rise of the ignition control signal IG (that is, the rise of the second signal IG 2 ) based on the signal input from the first AND circuit  514   a  to the CLK terminal. The output from the second D flip-flop  513   b  is input to the second AND circuit  514   b  via the first inverter circuit  515   a , and is output as the signal IGW_DCT for detecting the first rise and the subsequent rise of the ignition control signal IG. 
     The third D flip-flop  513   c  has a configuration equivalent to that of the first D flip-flop  513   a , and it is a circuit for detecting the first fall of the ignition control signal IG (that is, the fall of the first signal IG 1 ) based on the signal input from the second AND circuit  514   b  to the CLK terminal via the second inverter circuit  515   b . The output from the third D flip-flop  513   c  is input to the fourth AND circuit  514   d  via the third inverter circuit  515   c , and is output as the signal IGA_DCT for detecting the first rise and the fall of the ignition control signal IG. 
     Note that the reset signal RES from the reset signal generation circuit  55  is also input to the RES terminals of the second D flip-flop  513   b  and the third D flip-flop  513   c  so that their latches are reset at the same timing as the first D flip-flop  513   a.    
     The square wave signal  1   a  is input to one terminal of the first AND circuit  514   a , and a signal from the Q terminal of the third D flip-flop  513   c  is input to the other terminal. 
     When one terminal of the first AND circuit  514   a  shifts to the H level due to the fall of the square wave signal  1   a , and the other terminal shifts to the H level due to the second rise of the square wave signal  1   a  after that, at this timing, the first AND circuit  514   a  outputs a signal having the H level to the CLK terminal of the second D flip-flop  513   b . As a result, the output from the Q terminal will have the H level, and this output is input to one terminal of the second AND circuit  514   b  as a signal  1   b  inverted by the first inverter circuit  515   a.    
     That is, as shown in  FIG. 7 , the signal  1   b  is a signal that initially has the H level and shifts to the L level at the time of the second rise of the ignition control signal IG. The signal IGT_DCT from the Q terminal of the first D flip-flop  513   a  is input to the other terminal of the second AND circuit  514   b.    
     At this time, the second AND circuit  514   b  outputs a signal IGW_DCT, which has the H level when the signal  1   b  is at the H level and the signal IGT_DCT is at the H level. In other words, the signal IGW_DCT is a signal that rises when the signal IGT_DCT shifts to the H level and falls when the signal  1   b  shifts to the L level. 
     The signal IGT_DCT from the Q terminal of the first D flip-flop  513   a  is input to one terminal of the third AND circuit  514   c , and the square wave signal  1   a  is input to its other terminal via the second inverter circuit  515   b.    
     At this time, when the signal IGT_DCT is at the H level and the square signal  1   a  is at the L level, the third AND circuit  514   c  outputs a signal having the H level to the CLK terminal of the third D flip-flop  513   c . As a result, the output from the Q terminal will have the H level, and will be input to one terminal of the fourth AND circuit  514   d  as a signal  1   c  inverted by the third inverter circuit  515   c.    
     That is, as shown in  FIG. 7 , the signal  1   c  is a signal that initially has the H level and shifts to the L level at the time of the first fall of the ignition control signal IG. The signal IGT_DCT from the Q terminal of the first D flip-flop  513   a  is input to the other terminal of the fourth AND circuit  514   d.    
     At this time, the fourth AND circuit  514   d  outputs a signal IGA_DCT, which has the H level when the signal  1   c  is at the H level and the signal IGT_DCT is at the H level. In other words, the signal IGA_DCT is a signal that rises when the signal IGT_DCT shifts to the H level and falls when the signal  1   b  shifts to the L level. 
     As shown in  FIG. 8 , the IGT generation circuit  52  includes a waiting time generation circuit (hereinafter referred to as a t wait  generation circuit)  521  for generating the waiting time t wait , AND circuits  522 ,  523 , and an inverter circuit  524 . The square wave signal  1   a  and the signal IGT_DCT from the waveform shaping circuit  51  are input to the IGT generation circuit  52 , and the t wait  generation circuit  521  generates a signal  2   b  for confirming that the predetermined waiting time t wait  has been kept. The AND circuit  522  generates the main ignition signal IGT based on the signal  2   b  output from the t wait  generation circuit  521  and the square wave signal  1   a , and the AND circuit  523  generates a signal  2   c  based on a signal obtained by inverting the signal  2   b  from the t wait  generation circuit  521  by the inverter circuit  524  and the signal IGT_DCT. 
     The t wait  generation circuit  521  is formed by using, for example, a counter circuit including multiple stages (N stages) of JK flip-flop circuits  525 . The J terminal and K terminal of the JK flip-flop circuit  525  of the first stage are connected to a power supply to receive a potential corresponding to the H level. The signal  2   a  from the AND circuit  526  is input to the CLK terminal of the JK flip-flop circuit  525  of each stage, and the Q terminal of the JK flip-flop circuit  525  of each stage is connected to the J terminal and K terminal of the JK flip-flop circuit  525  of the subsequent stage. The Q terminal of the JK flip-flop circuit  525  of the final stage (Nth stage) is connected to the CLK terminal of the D flip-flop circuit  527 . 
     A reset signal RES from the reset signal generation circuit  55  is input to the clear terminal (hereinafter referred to as the CLR terminal) of the JK flip-flop circuit  525  of each stage so that they are reset when the reset signal RES switches from the H level to the L level. Similarly, a reset signal RES is input to the RES terminal of the D flip-flop circuit  527  so that it is reset when the reset signal falls. 
     The signal IGT_DCT and a clock signal from an external clock generation circuit are input to the AND circuit  526 . When the clock signal rises after the rise of the signal IGT_DCT, the signal  2   a  is output to the JK flipflop circuit  525  of each stage in synchronization with the clock signal. 
     Thus, as shown in  FIG. 9 , when the signal  2   a  from the AND circuit  526  rises to the H level after the signal IGT_DCT has risen to the H level in synchronization with the square wave signal  1   a , the counter operation is started. In the initial state, the output  3   a  of the first-stage JK flip-flop circuit  525 , the output  3   b  of the second-stage JK flip-flop circuit  525 , . . . . And the output  3   c  of the final-stage JK flip-flop circuit  525  are all at the L level. Then, each time the signal  2   a  is output, the output  3   a  of the first-stage JK flip-flop circuit  525  is inverted and input to the J terminal and K terminal of the second-stage JK flip-flop circuit  525 . Each time the output  3   a  of the first-stage JK flip-flop circuit  525  rises, the output  3   b  of the second-stage JK flip-flop circuit  525  is inverted, and similarly, the signal is transmitted to the JK flip-flop circuits  525  of the subsequent stages. 
     By repeating this sequentially, the output  3   c  of the final-stage JK flip-flop circuit  525  will be inverted by the input from the previous stage. Then, when an H level signal is input to the CLK terminal of the D flip-flop circuit  527 , the signal  2   b  output from the D flip-flop circuit  527  rises to the H level. 
     The number of stages of the JK flip-flop circuits  525  is appropriately set so that a time corresponding to the predetermined waiting time t wait  can be measured. 
     The main ignition signal IGT output from the AND circuit  522  rises to the H level after the waiting time t wait  from the rise of the square wave signal  1   a  in response to the signal  2   b  and the square wave signal  1   a  shifting to the H level. After that, the main ignition signal IGT falls to the L level in synchronization with the fall of the square wave signal  1   a . The signal  2   c  output from the AND circuit  523  has the H level during the period from the rise of the square wave signal  1   a  to the rise of the signal  2   b  in response to the inverted signal of the signal  2   b  and the signal IGT_DCT having the H level. This period corresponds to the waiting time t wait , and when the main ignition signal IGT rises, the signal  2   c  falls to the L level. 
     Further, after a predetermined reset period t reswait  from the fall of the square wave signal  1   a  and main ignition signal IGT, the reset signal RES falls. As a result, the latches of the JK flip-flop circuits  525  and the D flip-flop circuit  527  are reset similarly to the signal IGT_DCT. 
     The main ignition signal IGT is thus generated in response to the output of the square wave signal  1   a.    
     The IGW generation circuit  53  detects, for example, as shown in  FIG. 11 , the rising interval t IGW_IN  of the signal IGW_DCT using an up counter circuit  531  shown in  FIG. 10 , and uses the detected rising interval t IGW_IN  to generate the energy input signal IGW. The rising interval t IGW_IN  may be set as it is as the energy input period t IGW , or a value obtained by multiplying the rising interval t IGW_IN  with a predetermined coefficient (for example, 2 or ½) may be set as the energy input period t IGW . The IGW generation circuit  53  includes, for example, a down counter circuit having a structure equivalent to that of the up counter circuit  531 . 
     Specifically, in  FIG. 10 , the up counter circuit  531  includes a plurality of stages (N stages) of JK flip-flop circuits  532  and an AND circuit  533 . The J terminal and K terminal of the JK flip-flop circuit  532  of the first stage are connected to a power supply to receive a potential corresponding to the H level. The Q terminal is connected to the J terminal and K terminal of the second-stage JK flip-flop circuit  532 , and in addition, it is also connected to a bus line Lb leading to an N-bit bit counter (IGW_COUNTER). Likewise, the Q terminal of the JK flip-flop circuit  532  of each of the second and later stages is connected to the J terminal and K terminal of the JK flip-flop circuit  532  of the subsequent stage and the bus line Lb. 
     The signal IGW_DCT and a clock signal from a clock generation circuit (not shown) are input to the AND circuit  533 . Therefore, when the clock signal rises after the rise of the signal IGT_DCT, a signal from the AND circuit  533  is input to the CLK terminal of the JK flip-flop circuit  532  of each stage. 
     A reset signal RES from the reset signal generation circuit  55  is input to the CLR terminal of the JK flip-flop circuit  532  of each stage so that they are reset when the reset signal falls. 
     Thus, as shown in  FIG. 11 , when the signal from the AND circuit  533  rises to the H level after the signal IGW_DCT has risen to the H level in synchronization with the square wave signal  1   a , the counter operation is started by the up counter circuit  531 . In the initial state, the output of the first-stage JK flip-flop circuit  532  is at the L level, and the outputs of the JK flip-flop circuits  532  of the second and later stages are all at the L level. Then, when the signal from the AND circuit  533  is input to the CLK terminal of each stage, the output of the first-stage JK flip-flop circuit  532  is inverted and output to the bus line Lb and the J terminal and K terminal of the second-stage JK flip-flop circuit  532 . 
     That is, the output of the first-stage JK flip-flop circuit  532  switches to the H level, whereas the outputs of the subsequent stages remain at the L level. After that, each time a signal from the AND circuit  533  is input, the signal is transmitted to the JK flip-flop circuit  532  of the subsequent stage, and the outputs are sequentially switched to the H level. These outputs are output to the bit counter IGW_COUNTER via the bus line Lb so that the up counter circuit  531  can measure the time while the signal IGW_DCT is at the H level. 
     The measured length of the signal IGW_DCT is kept as the rising interval t IGW_IN  (that is, the interval from the first rise to the second rise of the square wave signal  1   a ). The IGW generation circuit  53  then raises the energy input signal IGW after a predetermined delay period t fil  from the second fall of the square wave signal  1   a , and starts counting down the time corresponding to the kept rising interval t IGW_IN . The down counter circuit can have a configuration similar to that of the up counter circuit  531 . 
     In this way, the energy input signal IGW is generated by outputting an H level signal during the energy input period t IGW  after the main ignition signal IGT. 
     As shown in  FIG. 12 , the IGA generation circuit  54  detects the rising period t IGA_IN  of the signal IGA_DCT, and uses the detected rising period t IGA_IN  to generate the target secondary current instruction signal IGA. The detection of the rising period t IGA_IN  of the signal IGA_DCT may be done using, for example, as with the above-described rising interval t IGW_IN , an up counter circuit having a configuration similar to that of the up counter circuit  531  shown in  FIG. 10 . 
     The rising period t IGA_IN  indicates the target secondary current value I 2   tgt  (absolute value) to be used in the energy input operation after the main ignition operation, like the example shown in Table 1 below. That is, the target secondary current value I 2   tgt  is expressed by a function f(t IGA_IN ) of the rising period t IGA_IN , and the target secondary current value I 2   tgt  is variably set according to the length of the rising period t IGA_IN . For example, when t IGA_IN &lt;0.25 ms, the target secondary current value I 2   tgt  may be set to 60 mA, when 0.25 ms≤t IGA_IN &lt;0.75 ms, the target secondary current value I 2   tgt  may be set to 90 mA, and when 0.75 ms≤t IGA_IN , the target secondary current value I 2   tgt  may be set to 120 mA. When no rise of t IGA_IN  is detected, the energy input operation is not performed and the target secondary current value I 2   tgt  is set to 0 mA. 
     
       
         
           
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 t IGA _IN 
                 I2tgt = f(t IGA _IN) 
               
               
                   
               
             
            
               
                 No fall detected during waiting time 
                 No energy input operation (0 mA) 
               
               
                 t IGA _IN &lt; 0.25 ms 
                  60 mA 
               
               
                 0.25 ms ≤ t IGA _IN &lt; 0.75 ms 
                  90 mA 
               
               
                 0.75 ms ≤ t IGA _IN 
                 120 mA 
               
               
                   
               
            
           
         
       
     
     Accordingly, the up counter circuit performs counting while the signal IGA_DCT is at the H level to detect the rising period t IGA_IN  (that is, the length from the first rise to the fall of the square wave signal  1   a ) and keep it. Next, when the energy input signal IGW rises after a predetermined delay period t fil  from the main ignition operation due to the second fall of the square wave signal  1   a , the secondary current feedback control is performed so that the target secondary current value I 2   tgt , which is set based on the rising period t IGA_IN , is maintained during the energy input period t IGW . 
     Specifically, based on the detected value of the secondary current I 2 , the secondary current feedback circuit  61  (see, for example,  FIG. 1 ) outputs a gate signal MOS_gate 1  and a gate signal MOS_gate 2  from the auxiliary primary coil control circuit  4  to control the on/off of the discharge continuation switch SW 2  and the flyback switch SW 3 , so that the secondary current I 2  is maintained around the target secondary current value I 2   tgt.    
     As shown in  FIG. 13 , the reset signal RES generation circuit  55  is configured by using, for example, a t reswait  generation circuit  551  that generates the reset period t reswait  and a reset pulse generation circuit  552  that generates the pulse reset signal RES. The AND circuit  553  connected to the input side of the t reswait  generation circuit  551  receives a signal obtained inverting the square wave signal  1   a  from the waveform shaping circuit  51  via the inverter circuit  554   a , and a signal  1   d  obtained by inverting the signal  1   b  for detecting the second rise via the inverter circuit  554   b , and a signal obtained by inverting the signal  2   c  inverted from the IGT generation circuit  52  via the inverter circuit  554   c.    
     The t reswait  generation circuit  551  may be configured by using a counter circuit (digital circuit) like the IGW generation circuit  53  and the IGA generation circuit  54  described above, but as shown in the figure, it may be configured as an analog circuit including a constant current source  555 , a capacitor C 2 , and a comparator CMP 1 . In the t reswait  generation circuit  551 , the switch SW 5  is turned on when the signal from the AND circuit  553  is at the H level, and the capacitor C 2  is connected to the constant current source  555  so that a constant current flows. As a result, the capacitor C 2  is charged, and the input potential  4   a  of the positive terminal of the comparator CMP 1  connected to the capacitor C 2  exceeds the reference potential supplied to the negative terminal. The signal  4   b  from the comparator CMP 1  then shifts to the H level. 
     One end of a resistor R 2  is grounded and its other end is connected between the capacitor C 2  and the comparator CMP 1 . and the time constant of the capacitor C 2  and the resistor R 2  can be used to adjust the predetermined reset period t reswait . Note that a resistor R 3  for discharging may be further provided in parallel with the resistor R 2 , and the line between it and the ground potential may be opened/closed using a switch SW 6  for discharging. For example, rapid discharge can be realized by turning on the switch SW 6  for discharging in synchronization with the latch resetting to connect the positive terminal side of the capacitor C 2  to the ground potential via the resistor R 3  for discharging. 
     Further, the reset pulse generation circuit  552  has a NAND circuit  556  that outputs reset signals RES. The NAND circuit  556  receives the signal  4   b  from the t reswait  generation circuit  551  and also the signal  4   c  from a delay circuit made up of inverter circuits  554   d ,  554   e  and a resistor R 4  and a capacitor C 3  placed between the inverter circuits. 
     As shown in  FIG. 14 , the output from the AND circuit  553  is initially at the L level, and it switches to the H level only when the square wave signal  1   a  is at the L level, the signal  1   b  is at the L level (signal  1   d  is at the H level), and the signal  2   c  is at the L level. That is, in the initial state, the switch SW 5  is off. After the elapse of the waiting time t wait  from the drop of the signal  1   b  to the L level in response to the second rise of the square wave signal  1   a , the signal  2   c  falls, and further the square wave signal  1   a  falls. Then, it is determined that the ignition control signal IG has ended, and the switch SW 5  is turned on. 
     This causes the potential of the capacitor C 2  to gradually rise, and when the input potential  4   a  to the comparator CMP 1  reaches a predetermined reference potential Vth RES , the signal  4   b  output from the comparator CMP 1  shifts to the H level. Then, when the switch SW 5  is turned off after the predetermined reset period t reswait  and the capacitor C 2  is discharged and its potential becomes lower than the reference potential Vth RES , the signal  4   b  from the comparator CMP 1  shifts to the L level. 
     The signal  4   b  it at the H level while the switch SW 5  is on and the input potential  4   a  is higher than the reference potential Vth RES . The signal  4   c  is a signal obtained by delaying the signal  4   b . Since the switch SW 5  is initially off, the output of the comparator CMP 1  is at the L level and the signal  4   c  is at the L level. The signal  4   c  and the signal  4   b  are input to the NAND circuit  558 , and the reset signal RES output from it has the L level only when both of these signals are at the H level. 
     That is, the reset signal RES is at the H level in the initial state, and when the switch SW 5  is turned on in response to the second fall of the square wave signal  1   a , the signal  4   b  shifts to the H level with a certain delay. When the signal  4   c  obtained by delaying the signal  4   b  shifts to the H level, the reset signal RES falls to the L level. As a result, the latch of each circuit is reset, the signal  1   d  shifts to the L level, the switch SW 5  is turned off, and the capacitor C 2  is discharged, which causes the signal  4   b , which is the output of the comparator CMP 1 , to shift to the L level after a predetermined time period tdischg. This in turn causes the reset signal RES to rise to the H level again and return to the initial state. 
     The reset pulse signal RES can be output from the reset pulse generation circuit  552  in such a manner. Note that the reset period t reswait  is set to be longer than the energy input period t IGW  in order to prevent the reset operation being carried out during the energy input operation. Preferably, in consideration of the delay period t fil  after the main ignition operation, the period during which the switch SW 5  is on corresponding to the reset period t reswait  is set as appropriate so that the reset operation is performed after the energy input period t IGW  has elapsed. 
     As described above, according to the present embodiment, the engine ECU  100  transmits the ignition control signal IG including information for the main ignition signal IGT, the energy input signal IGW, and the target secondary current instruction signal IGA to the ignition device  10  in advance. The transmitted ignition control signal can be separated into the individual signals in the signal separation circuit unit  5 . The separated signals are output at certain timings to perform the main ignition operation and the energy input operation. That is, the engine ECU  100  outputs the ignition control signal IG at a timing that is earlier than the output of the main ignition signal IGT by the waiting time t wait . Since the signals required for main ignition and energy input can be generated in advance, it is possible to reduce the number of signal lines connecting the devices and implement the ignition control device  1  capable of suppressing the influence of noise and other influences with a simple configuration. 
     Note that the ignition control signal IG does not necessarily have to consist of the first signal IG 1  and the second signal IG 2 . For example, it may be a signal that rises at a timing that is earlier than the rise of the main ignition signal IGT by the waiting time t wait , and falls at the same timing as the main ignition signal IGT. In that case, a single ignition control signal IG that is longer than the main ignition signal IGT by the waiting time t wait  is output from the engine ECU  100  at a timing earlier than the output of the main ignition signal IGT by the waiting time t wait . This enables application to a normal ignition operation that does not involve energy input. 
     Examples of modifications of the above-described ignition control signal IG will be described with reference to the following second to fourth embodiments. 
     Second Embodiment 
     The second embodiment according to the ignition control device will be described with reference to  FIG. 15 . 
     In the first embodiment, a case has been described where the ignition control signal IG is separated into individual signals in the signal separation unit  5  of the ignition control device  1  shown in  FIG. 1  to carry out the main ignition operation and the energy input operation. In this embodiment, the signal waveform of the ignition control signal IG is different, and only the main ignition operation is performed based on the main ignition signal IGT generated by being separated from the ignition control signal IG. The differences will be mainly described. 
     Note that, among the reference signs used in the second and following embodiments, reference signs that are the same as those used in an earlier embodiment denote components or the like that are similar to those of the earlier embodiment unless otherwise noted. 
     The basic configuration and operation of the ignition control device  1  of this embodiment are the same as those of the first embodiment, and their description will be omitted. 
     As shown in  FIG. 15 , the ignition control signal IG formed of one pulse signal, and it is received as a signal that substantially combines the first pulse signal IG 1  and the second pulse signal IG 2  together. In this case, the square wave signal  1   a  obtained by shaping the waveform of the ignition control signal IG is also a single pulse signal, and the main ignition signal IGT is generated based on its rising and falling edges. 
     Specifically, the waveform shaping circuit  51  of the signal separation circuit unit  5  shapes the waveform of the ignition control signal IG and outputs the obtained square wave signal  1   a , and when the waiting time t wait  has passed from the rise of the square wave signal  1   a  and the signal level is the H level in the IGT generation circuit  52 , the main ignition signal IGT rises at that time point. When the signal level of the square wave signal  1   a  shifts to the L level after the rising, the main ignition signal IGT falls at that time point. The main ignition signal IGT is thus generated. 
     In accordance with this, the main ignition drive circuit  31  drives the main ignition switch SW 1 . Energization of the main primary coil  21   a  starts at the time at which the main ignition signal IGT rises so that the primary current I 1  flows. Then, by cutting off the energization of the main primary coil  21   a , a high voltage is generated in the secondary coil  22  and the secondary current I 2  flows. 
     Similarly, the IGW generation circuit  53  and the IGA generation circuit  54  generate the energy input signal IGW and the target secondary current instruction signal IGA based on the square wave signal  1   a . However, since no falling or second rising of the square wave signal  1   a  is detected during the waiting time t wait  from the rise of the square wave signal  1   a , the energy input signal IGW and the target secondary current instruction signal IGA remain at the L level, and therefore the energy input operation will not be performed. 
     By forming the ignition control signal IG such that it has a signal waveform including one or two pulses as described above, it is possible to start the main ignition operation and also indicate whether to perform the energy input operation. When the energy input operation is not to be performed, the signal from the engine ECU  100  is set such that the rising period t IGT  of the main ignition signal IGT required for the engine operating conditions is started during the waiting time t wait  That is, the waiting time t wait  overlaps with the rising period t IGT , and the ignition control signal IG is transmitted as one signal in which the first signal IG 1  and the second signal IG 2  cannot be distinguished. In other words, the device can be easily applied to cases where only the main ignition operation is performed and the energy input is not by transmitting the signal from the engine ECU  100  at a timing that is earlier than the rising period t IGT  by the waiting time t wait . 
     Further, it can be determined that no rising signal of the ignition control signal IG is detected during the waiting time t wait  when the IGW_counter of the IGW generation circuit has a count corresponding to the waiting time t wait . In that case, since the energy input operation becomes unnecessary, the counters for the main ignition signal IGT, the energy input signal IGW, the target secondary current instruction signal IGA, and the like can be quickly reset after a predetermined delay period t fil  from the main ignition operation. This makes it possible to proceed to the next ignition operation without waiting for the reset period t reswait  to pass. 
     Third Embodiment 
     The third embodiment according to the ignition control device will be described with reference to  FIG. 16 . 
     In the second embodiment, a case has been described where only the main ignition operation is performed based on the signal waveform of the ignition control signal IG in the ignition control device  1  shown in  FIG. 1 . In the present embodiment, an example case is described where whether to perform the main ignition operation is determined based on the waiting time t wait  in the signal waveform, and the main ignition operation is not performed. 
     The basic configuration and operation of the ignition control device  1  of this embodiment are the same as those of the first and second embodiments, and the differences will be mainly discussed. 
     The ignition control signal IG shown in the left part [A] of  FIG. 16  is formed of one pulse signal, and, for example, has a relatively short pulse width corresponding to the first signal IG 1 . In this case, when the waiting time t wait  has passed from the rise of the square wave signal  1   a  obtained by waveform-shaping, the signal level shifts to the L level and the main ignition signal IGT is not output. 
     Specifically, when the waveform shaping circuit  51  of the signal separation circuit unit  5  shapes the waveform of the ignition control signal IG and outputs the obtained square wave signal  1   a , the target secondary current instruction signal IGA is generated in the IGA generation circuit  54  based on its rising period t IGA_IN . However, since a signal corresponding to the second signal IG 2  is not received after that, and no second rise of the square wave signal  1   a  is detected during the waiting time t wait  from the rise of the square wave signal  1   a , the main ignition signal IGT and the energy input signal IGW will not be output. 
     Energization of the main primary coil  21   a  will not be started, and the primary current I 1  will not flow. That is, the main ignition operation and the energy input operation will not be performed, and the secondary current I 2  and the current I NET  will not flow either. 
     Therefore, if the main ignition operation becomes unnecessary for some reason such as a change in the engine operating conditions after receiving the first signal IG 1 , the main ignition operation can be stopped by stopping the transmission of the second signal IG 2  from the engine ECU  100 . 
     Further, for example, when noise caused by the ignition operation of another cylinder or another unintended signal is input, even if the signal separation circuit unit  5  regards it as the first signal IG 1 , the main ignition signal IGT is not generated if the second signal IG 2  is not input. This prevents erroneous operation. 
     As shown in the right part [B] of  FIG. 16 , even when the ignition control signal IG is composed of two pulse signals, if the signal level of the second signal IG 2  shifts to the L level before the elapse of the waiting time t wait  from the rise of the square wave signal  1   a , the main ignition signal IGT will not be generated. In this case, since a second rise of the square wave signal  1   a  is detected during the waiting time t wait  after the rise of the square wave signal  1   a , the rising interval  IGW_IN  will be set but the main ignition signal IGT will not be output, and therefore the energy input signal IGW will not be output. 
     Accordingly, even after the transmission of the second signal IG 2  from the engine ECU  100  has started, it is possible to stop the main ignition operation by stopping the transmission of the second signal IG 2  before the waiting time t wait  elapses. 
     With such a configuration, for example, even when external pulse noise similar to the first signal IG 1  is input to the ignition device  10 , if no subsequent second signal IG 2  is input, the main ignition signal IGT will not be generated. Therefore, the ignition control device  1  can have high resistance to noise so that it would not start the main ignition operation based on erroneous signals. 
     Fourth Embodiment 
     The fourth embodiment according to the ignition control device will be described with reference to  FIGS. 17 and 18 . 
     The third embodiment presents the relationship between the waiting time t wait  in the waveform of the ignition control signal IG and the main ignition operation in the ignition control device  1  shown in  FIG. 1 . In the present embodiment, an example case is described where the waiting time t wait  in the signal waveform is variable depending on the engine operating conditions. 
     The basic configuration and operation of the ignition control device  1  of this embodiment are the same as those of the first to third embodiments, and the differences will be mainly discussed. 
     In  FIG. 17 , the ignition control signal IG shown on the left and the ignition control signal IG shown on the right have the same waveform composed of the first signal IG 1  and the second signal IG 2 , but they have different waiting time t wait , which is variably set according to one or more engine operating conditions. The engine operating condition is, for example, the engine speed, and the higher the engine speed, the shorter the set waiting time t wait . 
     Specifically, as shown in the left part of  FIG. 17 , in a case where the engine speed is in the low rotation speed range, for example, 1000 rpm (in other words, the period is 120 ms), the waiting time t wait  is set longer so that the second signal IG 2  falls before the elapse of the waiting time t wait . In this case, since the signal level of the square wave signal  1   a  is the L level when the waiting time t wait  has passed, only the target secondary current instruction signal IGA is output as in the third embodiment. That is, the main ignition signal IGT is not output and the main ignition operation is not performed. 
     For example, the waiting time can be set so that, like a hybrid vehicle, the vehicle is motor driven in a predetermined low rotation region by stopping the ignition operation. In that case, the waiting time t wait  is set to be long in the corresponding low rotation region so that the second signal IG 2  falls before the elapse of the waiting time t wait . This provides a setting with which the main ignition signal IGT is not output and the main ignition operation is not performed. 
     On the other hand, as shown in the right part of  FIG. 17 , in a case where the engine speed is in the high rotation speed range, for example, 6000 rpm (in other words, the period is 20 ms), the waiting time t wait  is set shorter so that the second signal IG 2  falls after the elapse of the waiting time t wait . The signal level of the square wave signal  1   a  is the H level when the waiting time t wait  has passed, and the signal separation circuit unit  5  outputs the main ignition signal IGT, the energy input signal IGW, and the target secondary current instruction signal IGA as in the first embodiment. 
     Energization of the main primary coil  21   a  starts in synchronization with the rise of the main ignition signal IGT and the primary current I 1  flows. The secondary current I 2  flows when the energization is cut off. Further, during the period specified by the energy input signal IGW, the energy input operation set by the target secondary current instruction signal IGA is performed. The secondary current I 2  is maintained and the current I NET  flows. 
     Since the ignition cycle period changes when the engine speed changes, it is desirable that the waiting time t wait  is set so that the main ignition signal IGT is output at an energization timing in accordance with the ignition timing. As described earlier, the main ignition signal IGT rises when the waiting time t wait  has passed from the rise of the square wave signal  1   a  and the signal level is the H level. Therefore, it is desirable to set the waiting time t wait  shorter in the high rotation range in which the ignition cycle becomes shorter. 
     As shown in  FIG. 18 , when the waiting time t wait  is changed according to the engine operating conditions, for example, the engine speed, it may be changed continuously or stepwise. Specifically, the waiting time t wait  may be set such that the waiting time t wait  decreases continuously as the rotation speed increases as shown in the left graph, or the waiting time t wait  is constant until the rotation speed reaches a certain rotation speed N 1 , and decreases stepwise after that each time the rotation speed reaches higher rotation speeds N 2 , N 3  as shown in the right graph. 
     Fifth Embodiment 
     The fifth embodiment according to the ignition control device will be described with reference to  FIGS. 19 to 21 . 
     This embodiment presents an example of the process of the main ignition operation and the process of the energy input operation performed using the ignition device  10  of the ignition control device  1  according to the first embodiment. 
     As shown in  FIG. 1 , the ignition device  10  receives the ignition control signal IG transmitted from the engine ECU  100  at the signal separation circuit  5 , and transmits the main ignition signal IGT separated therefrom to the main ignition drive circuit  31  of the main ignition circuit unit  3  and also to the auxiliary primary coil control circuit  41  of the energy input circuit unit  4 . 
     The flowchart shown in  FIG. 19  shows the procedures executed in order to generate individual signals by separating them from the ignition control signal IG in the ignition device  10 .  FIG. 20  shows the same flowchart with arrows for comparing the processes of the first to third embodiments. Each of the first to third embodiments separates the individual signals from a different ignition control signal IG through a different process. The time chart shown in  FIG. 21  corresponds to the first embodiment. The ignition control signal IG includes the first signal IG 1  and the second signal IG 2  as shown in  FIG. 2  referred to earlier, and both the main ignition operation and the energy input operation are carried out. 
     The procedures of the first embodiment will mainly be described with reference to  FIG. 21 . 
     In  FIGS. 19 and 20 , when the signal separation process is started in the signal separation circuit  5 , first, it is determined in step  101  whether a rise of the ignition control signal IG is detected. Here, it is determined whether the first rise of the square wave signal  1   a  (that is, the rise of the first signal IG 1 ) obtained by shaping the waveform of the ignition control signal IG by the waveform shaping circuit  51  is detected. 
     When the answer is Yes in step  101 , the process proceeds to step  102 , and when the answer is No, step  101  is repeated until the answer becomes Yes. 
     In step  102 , the IGA generation circuit  54  starts the detection of the rising period t IGA_IN  of the square wave signal  1   a , and the IGW generation circuit  53  starts the detection of the rising interval t IGA_IN  of the square wave signal  1   a . The rising period t IGA_IN  is the period from the first rise to the fall of the square wave signal  1   a , and, in the first embodiment, it corresponds to the rising period of the first signal IG 1 . The rising interval t IGW_IN  is the period from the first rise to the second fall of the square wave signal  1   a , and, in the first embodiment, it corresponds to the interval between the rise of the first signal IG 1  and the rise of the second signal IG 2 . 
     Next, in step  103 , the IGA generation circuit  54  determines whether the first fall of the square wave signal  1   a  (that is, the fall of the first signal IG 1 ) is detected. When the answer is Yes in step  103 , the process proceeds to step  104 , and when the answer is No, the process proceeds to step  105 . 
     When the answer is Yes in step  103 , in step  104 , the rising period t IGA_IN  is confirmed and also the target secondary current value I 2   tgt , which is represented by a function of the rising period f (t IGA_IN ), is confirmed. 
     As shown in  FIG. 21 , in the first embodiment, the rising period t IGA_IN  of the square wave signal  1   a  is detected by detecting the rise and fall of the first signal IG 1  (for example, 0.5 ms). Along with this, the target secondary current instruction signal IGA output from the IGA generation circuit  54  gradually rises and then is maintained at a constant value. The target secondary current value I 2   tgt  is variably set according to the length of the rising period t IGA_IN , and as shown in Table 1 above, for example, when the rising period is 0.5 ms, the target secondary current value I 2   tgt  is 90 mA. 
     Next, in step  106 , the IGW generation circuit  53  determines whether the second rise of the square wave signal  1   a  (that is, the rise of the second signal IG 2 ) is detected. When the answer is Yes in step  106 , the process proceeds to step  107 , and when the answer is No, the process proceeds to step  108 . 
     When the answer is Yes in step  106 , in step  107 , the rising interval t IGW_IN  is confirmed and also the energy input period t IGW  is confirmed based on the rising interval. 
     As shown in  FIG. 21 , in the first embodiment, the rising interval t IGW_IN  of the square wave signal  1   a  is detected by detecting the rise of the first signal IG 1  and the rise of the second signal IG 2  (for example, 2.5 ms). Along with this, the energy input period t IGW  having a length equivalent to that of the rising interval t IGW_IN  is set (for example, 2.5 ms), and the energy input signal IGA is output after a predetermined waiting time t wait . 
     Next, in step  109 , it is determined whether the predetermined waiting time t wait  has been reached. The waiting time t wait  is separately generated by the t wait  generation circuit  521  of the IGT generation circuit  52  as the time from the rise of the square wave signal  1   a . When the answer is Yes in step  109 , the process proceeds to step  110  to start the energy supply operation. The energy supply operation refers to the main ignition operation and the energy input operation, and both of them are carried out in the first embodiment. 
     Specifically, first, in step  111 , it is determined whether the signal level of the square wave signal  1   a  is the H level, and the process proceeds to step  112  when the answer is Yes. In step  112 , the gate signal IGBT_gate output from the main ignition drive circuit  31  is set to the H level to turn on the main ignition switch SW 1 . 
     As a result, as shown in  FIG. 21 , the main ignition signal IGT rises, energization of the primary coil  21  for the main ignition operation is started, and the primary current I 1  flows. 
     When the answer is No in step  111 , the process proceeds to step  116 . 
     In step  113 , it is determined whether the signal level of the square wave signal  1   a  is the L level, and the process proceeds to step  114  when the answer is Yes. In step  114 , the gate signal IGBT_gate is set to the L level to turn off the main ignition switch SW 1 . 
     As a result, as shown in  FIG. 21 , the main ignition signal IGT falls (for example, after 4 ms from the rise) and the energization of the primary coil  21  is interrupted. Then, the high voltage generated in the secondary coil  22  causes the spark plug P to generate a spark discharge. 
     After that, in step  115 , the energy input operation is performed. Specifically, the gate signals MOS_gate 1  and MOS_gate 2  for the energy input operation are output from the auxiliary primary coil control circuit  41  at a certain timing based on the target secondary current value I 2   tgt  and the energy input period t IGW  confirmed in steps  104  and  107  described above in order to drive the discharge continuation switch SW 2  and the flyback switch SW 3 . 
     As a result, as shown in  FIG. 21 , the energy input operation is started after a predetermined delay period t fil  (for example, 0.1 ms) from the fall of the main ignition signal IGT. The energy input operation is performed to maintain the target secondary current value I 2   tgt  (for example, 90 mA) for the predetermined energy input period t IGW  (for example, 2.5 ms), and the secondary current I 2  and the current I NET  flow. 
     After that, the process proceeds to step  116  to reset the energy input period t IGW  and the target secondary current value I 2   tgt  for the energy input operation. This iteration of the process then ends. 
     As a result, as shown in  FIG. 21 , the setting for the energy input operation is reset to the initial state after a predetermined reset period t reswait  from the fall of the square wave signal  1   a  (for example, after 4 ms from the fall). 
     In this way, the main ignition signal IGT, the energy input signal IGW, and the target secondary current instruction signal IGA can be generated from the ignition control signal IG of the first embodiment, to perform the main ignition operation and the energy input operation. 
     In the case of the ignition control signal IG of the second embodiment, a fall of the square wave signal  1   a  is not detected in step  103  described above, and therefore the answer is No. In this case, the process proceeds to step  105  to determine whether the predetermined waiting time t wait  has been reached. The actions taken in step  105  and the subsequent steps are substantially the same as those of step  109  and the subsequent steps described above, and when the answer is Yes in step  105 , the process proceeds to step  117  to start the energy supply operation. 
     When the answer is No in step  105 , the process returns to step  102  to repeat the actions of step  102  and the subsequent steps. 
     When the energy supply operation is to be started, specifically, first, in step  118 , it is determined whether the signal level of the square wave signal  1   a  is the H level. When the answer is Yes, the process proceeds to step  119  to set the gate signal IGBT_gate to the H level and turn on the main ignition switch SW 1 . 
     When the answer is No in step  118 , the process proceeds to step  122 . 
     In step  120 , it is determined whether the signal level of the square wave signal  1   a  is the L level. When the answer is Yes, the process proceeds to step  121  to set the gate signal IGBT_gate to the L level and turn off the main ignition switch SW 1 . As a result, the energization of the primary coil  21  is interrupted, and the high voltage generated in the secondary coil  22  causes the spark plug P to generate a spark discharge. 
     Since the energy input operation is not carried out after the main ignition operation in the second embodiment, the process then proceeds to step  122  to reset the energy input period t IGW  and the target secondary current value I 2   tgt  for the energy input operation after the reset period t reswait  has passed from the fall of the square wave signal  1   a . This iteration of the process then ends. 
     In this way, the main ignition signal IGT for the main ignition operation can be generated from the ignition control signal IG of the second embodiment. 
     In the case of the ignition control signal IG of the third embodiment [A], the second rise of the square wave signal  1   a  is not detected in step  106  described above, and therefore the answer is No. In this case, the process proceeds to step  108  to determine whether the predetermined waiting time t wait  has been reached. The actions taken in step  108  and the subsequent steps are substantially the same as those of step  109  and the subsequent steps described above, and when the answer is Yes in step  108 , the process proceeds to step  117  to start the energy supply operation. When the answer is No in step  108 , the process returns to step  106  to repeat the actions of step  106  and the subsequent steps. 
     When the energy supply operation is started in step  117 , in the subsequent step  118 , it is determined whether the signal level of the square wave signal  1   a  is the H level. 
     In the case of the third embodiment [A], the answer of step  118  is No since the square wave signal  1   a  falls before the elapse of the waiting time t wait . In this case, the process then proceeds to step  122  to reset the energy input period t IGW  and the target secondary current value I 2   tgt  for the energy input operation after the elapse of the reset period t reswait  from the fall of the square wave signal  1   a . This iteration of the process then ends. 
     Note that, since the square wave signal includes the first signal IG 1  and the second signal IG 2  in the case of the third embodiment [B], the second rise of the square wave signal  1   a  is detected in step  106  described above. In that case, the flow is similar to that of the first embodiment. The process proceeds to step  107 , and the energy input period t IGW  is confirmed based on the rising interval t IGW_IN . After that, the process proceeds to step  109  to determine whether the predetermined waiting time t wait  has been reached. When the answer is Yes in step  109 , the process proceeds to step  110  to start the energy supply operation. When the answer is No in step  109 , the process returns to step  106  to repeat the actions of step  106  and the subsequent steps. 
     When the energy supply operation is started in step  110 , in the subsequent step  111 , it is determined whether the signal level of the square wave signal  1   a  is the H level. 
     In the case of the third embodiment [B], the answer of step  111  is No since both the first signal IG 1  and the second signal IG 2  fall before the elapse of the waiting time t wait . In this case, the process then proceeds to step  116  to reset the energy input period t IGW  and the target secondary current value I 2   tgt  for the energy input operation after the elapse of the reset period t reswait  from the fall of the square wave signal  1   a . This iteration of the process then ends. 
     As described above, in the cases of the ignition control signals IG of the third embodiment [A] and [B], the main ignition signal IGT is not generated by being separated by the signal separation circuit  5 , and the main ignition operation and the energy input operation are not performed. 
     Sixth Embodiment 
     The sixth embodiment according to the ignition control device will be described with reference to  FIGS. 22 to 29 . 
     The present embodiment presents another configuration example of the IGT generation circuit  52  of the ignition device  10  of the ignition control device  1  according to the first embodiment for generating the main ignition signal IGT by separating it from the ignition control signal IG received by the signal separation circuit  5 . In addition, other configuration examples of the IGW generation circuit  53  for generating the energy input signal IGW by separating it from the ignition control signal and the IGA generation circuit  54  for generating the target secondary current instruction signal IGA by separating it from the ignition control signal are presented. 
     In  FIG. 22 , the IGT generation circuit  52  includes the t wait  generation circuit  521  for generating the waiting time t wait , the AND circuits  522 ,  523 , and the inverter circuit  524 . As with the first embodiment, the square wave signal  1   a  and the signal IGT_DCT are input from the waveform shaping circuit  51  to the IGT generation circuit  52 , and the main ignition signal IGT and the signal  2   c  are generated based on the signal  2   b  output from the t wait  generation circuit  521  and the square wave signal  1   a.    
     In the first embodiment, as shown in  FIG. 8 , the t wait  generation circuit  521  forming a part of the IGT generation circuit  52  is implemented as a digital circuit using a counter circuit. In this embodiment, as shown in the figure, it is implemented as an analog circuit including a constant current source  528 , a capacitor C 4 , and a comparator CMP 2 . The constant current source  528  and the capacitor C 4  are connected via a switch SW 7 , and a resistor R 5  is provided in parallel with the capacitor C 4 . The switch SW 7  is turned off in the initial state, and is turned on when the signal IGT_DCT is at the H level. 
     As shown in  FIG. 23 , when the square wave signal  1   a  and the signal IGT_DCT from the waveform shaping circuit  51  rise, a constant current flows from the constant current source  528  to the capacitor C 4 , and the voltage signal  5   a  input to the positive terminal of the comparator CMP 2  increases gradually. When the voltage of the capacitor C 4  reaches the reference potential Vth 2  input to the negative terminal of the comparator CMP 2 , the signal  2   b  output from the comparator CMP 2  shifts to the H level. 
     The time from when the signal IGT_DCT reaches the H level until the signal  2   b  reaches the H level in the t wait  generation circuit  521  corresponds to the predetermined waiting time t wait . When the signal  2   b  reaches the H level after the waiting time t wait , the output of the AND circuit  522  based on the logical sum of the signal  2   b  and the square wave signal  1   a  shifts to the H level. That is, the main ignition signal IGT can be set to the H level only when the square wave signal  1   a  is at the H level after the waiting time t wait  has passed. 
     Note that an inverted signal of the signal  2   b  and the signal IGT_DCT are input to the AND circuit  523 , and the signal  2   c  output based on the logical product of these signals is at the H level during the predetermined waiting time t wait . 
     Alternatively, as shown in  FIG. 24 , the t wait  generation circuit  521  of the IGT generation circuit  52  may be configured as a delay circuit including a plurality of inverter circuits  524   a ,  524   b  and a CR time constant circuit. The CR time constant circuit is a circuit that uses the time constant of the capacitor C 5  and the resistor R 6 , and the inverter circuits  524   a ,  524   b  are connected to the input side and the output side of it, respectively. 
     In that case, as shown in  FIG. 25 , when the signal IGT_DCT from the waveform shaping circuit  51  rises, the t wait  generation circuit  521  outputs a signal  5   b  having a delayed waveform. Since the signal  5   b  rises gradually, it takes some time to reach the reference potential Vth 3 , and the signal  2   b , which is a signal inverted twice from the signal  5   b , remains at the L level. When the reference potential Vth 3  is reached, the signal  5   b  shifts to the H level, and the signal  2   b  also rises to the H level. 
     Therefore, it is also possible to output the main ignition signal IGT by making the delay time in the t wait  generation circuit  521  correspond to the predetermined waiting time t wait . In that case, since it is not necessary to use a comparator, reference voltage, a constant current source, and the like, the circuit configuration can be simplified. 
     Further, the waiting time t wait  may be detected using the counter of the digital circuit. 
     As shown in  FIG. 26 , the IGW generation circuit  53  may be implemented using an analog integrator circuit. 
     Specifically, the IGW generation circuit  53  includes an integrator circuit  534  including an operational amplifier AMP, a resistor R IGW , and a capacitor C IGW , a comparator COMP, an AND circuit  535 , an inverter circuit  536 , a plurality of switches SW 1   IGW  to SW 3   IGW , and a reset switch RES IGW . The signal IGW_DCT is input to the integrator circuit  534  from the waveform shaping circuit  51 , and the output from the integrator circuit  534  is input to one terminal of the AND circuit  535  via the comparator COMP. A signal obtained by inverting the square wave signal  1   a  from the waveform shaping circuit  51  via the inverter circuit  536  is input to the other terminal of the AND circuit  535 . 
     The switch SW 1   IGW  connected to a power supply (for example, 5V) and the switch SW 2   IGW  connected to the ground potential are switchably connected (or connected in a mutually exclusive manner) to the input side of the integrating circuit  534 , and the switch SW 3   IGW  is interposed between the resistor R IGW  and the capacitor C IGW . The reset switch RES IGW  is connected between the two terminals of the capacitor C IGW . 
     As shown in  FIG. 27 , in the initial state, the switch SW 1   IGW  is on and the switches SW 2   IGW  and SW 3   IGW  are off. Then, the switch SW 3   IGW  is turned on when the rise of the signal IGW_DCT is detected. Energization of the capacitor C IGW  starts, and the capacitor C IGW  is charged while the signal IGW_DCT is at the H level. The charging time is converted to the voltage VC IGW . After that, the switches SW 1   IGW , SW 3   IGW  are turned off when the second rise of the signal IGW_DCT is detected, and thus the voltage VC IGW  of the capacitor C IGW  is maintained. The switch SW 2   IGW  is turned on to prepare for the discharging of the electric charge of the capacitor C IGW . 
     During that time, an inverted signal of the square wave signal  1   a  is input to the AND circuit  535 , but the input to the comparator COMP is below the reference voltage Vth IGW  and the energy input signal IGW remains at the L level. Then, when the waiting time t wait  generated by the IGT generation circuit  52  has passed and the square wave signal  1   a  is at the H level, the switch SW 3   IGW  is turned on after a certain delay period t fil  from the fall of the square wave signal  1   a  (the main ignition discharge) so that the charge of the capacitor C IGW  is discharged. 
     As a result, the output from the comparator COMP increases and the output from the AND circuit  535  shifts to the H level. The voltage VC IGW  of the capacitor C IGW  gradually decreases over a discharge time corresponding to the charging time, and the energy input signal IGW having the H level is output with the energy input period t IGW  being the period until the voltage falls below the reference voltage Vth IGW . After that, the switches SW 1   IGW  to SW 3   IGW  return to the initial state. 
     As shown in  FIG. 28 , the IGA generation circuit  54  may be implemented as an analog circuit. Specifically, instead of using the up counter circuit as in the first embodiment, the IGA generation circuit  54  uses a constant current source  541  and a capacitor C IGA  to detect, from the signal IGA_DCT based on the square wave signal  1   a , the rising period t IGA_IN  thereof. The constant current source  541  and the capacitor C IGA  are connected via a switch SW 1   IGA , and a switch SW 2   IGA  is provided in parallel with the capacitor C IGA . 
     As shown in  FIG. 29 , in the initial state, the switch SW 1   IGA  is off and the switch SW 2   IGA  is on. Then, the switch SW 1   IGA  is turned on and the switch SW 2   IGA  is turned off when the rise of the signal IGA_DCT is detected. The capacitor C IGA  is charged while the signal IGA_DCT is at the H level, and the target secondary current instruction signal IGA increases. When the signal IGA_DCT shifts to the L level, the switches SW 1   IGA , SW 2   IGA  are turned off so that the target secondary current instruction signal IGA is maintained. 
     After that, when the waiting time t wait  generated by the IGT generation circuit  52  has passed and the square wave signal  1   a  is at the H level, the main ignition discharge is performed at the time the square wave signal  1   a  falls, and after a further delay time t fil , the energy input signal IGW rises. As a result, the energy input operation is performed based on the target secondary current instruction signal IGA during the energy input period t IGW . As with Table 1 of the first embodiment, the target secondary current instruction signal IGA is set so that, for example, the larger the voltage value, the larger the target secondary current value I 2   tgt . When the energy input signal IGW falls, the switches SW 1   IGA , SW 2   IGA  return to the initial state. 
     As described above, the IGT generation circuit  52 , the IGW generation circuit  53 , and the IGA generation circuit  54  can have various configurations implemented using a digital circuit or an analog circuit. 
     Seventh Embodiment 
     The seventh embodiment according to the ignition control device will be described with reference to  FIG. 30 . 
     In the above embodiment, the primary coil  21  of the ignition coil  2  is composed of the main primary coil  21   a  and the auxiliary primary coil  21   b , and it is connected in parallel with the DC power source B. Alternatively, as shown in  FIG. 30 , the ignition coil  2  may be composed of the primary coil  21  and the secondary coil  22 . Further, the energy input circuit unit  4  may be provided with a booster circuit  42  and a capacitor  43  so that the energy stored in the capacitor  43  is supplied to the ground side of the primary coil  21  in a superimposed manner. 
     In the present embodiment, the booster circuit  42  includes a switching element for boosting (hereinafter referred to as a boost switch) SW 8 , a boost driver circuit  421  for driving the boost switch SW 8 , a choke coil  422 , and a diode  423 . The boost driver circuit  421  switches the boost switch SW 8  to store the energy generated in the choke coil  422  in the capacitor  43 . A discharge continuation switch SW 9  is connected between the primary coil  21  and the main ignition switch SW 1  via the diode  44 , and is driven by an energy input driver circuit  45 . The forward direction of the diode  423  is the direction toward the capacitor  43 , and the forward direction of the diode  44  is the direction toward the primary coil  21 . 
     The boost driver circuit  421  is driven based on the main ignition signal IGT and charges the capacitor  43  during the main ignition operation. The energy input driver circuit  45  drives the discharge continuation switch SW 9  in the energy input period t IGW  after the main ignition operation based on the target secondary current instruction signal IGA and the energy input signal IGW so as to input the energy stored in the capacitor  43  to the ground side of the primary coil  21  in a superimposed manner. Such a configuration is also capable of making the spark discharge continue by carrying out the energy input operation by increasing a current having the same polarity as the secondary current I 2 . 
     The configurations of the ignition coil  2  and the energy input circuit unit  4  can be changed as appropriate as with these examples. For example, the booster circuit  42  of the seventh embodiment may be provided in the configuration of the first embodiment to supply electricity from the booster circuit  42  to the auxiliary primary coil  21   b  to perform the energy input operation. Further, more than one, for example, two ignition coil  2  pairs, each composed of a primary coil  21  and a secondary coil  22 , may be provided, and one of the ignition coils  2  may perform the main ignition operation whereas the other ignition coil  2  is used to perform the energy input operation. 
     The present disclosure is not limited to the above embodiments, and can be applied to various embodiments without departing from the gist of the present disclosure. For example, the ignition control signal IG has been described as a positive logic signal whose logic level is “1” when the signal voltage is at the H level, but it may be a negative logic signal that has a logic level opposite to the potential. The same applies to signals other than the ignition control signal IG, and it can be set as appropriate. 
     The internal combustion engine to which the ignition control device  1  is applied may be a gasoline engine for automobiles or any of various spark-ignition internal combustion engines. The configurations of the ignition coil  2  and the ignition device  10  may be appropriately changed according to the internal combustion engine to which they are applied, as long as they can perform the energy input operation after the main ignition operation. For example, two ignition coil  2  pairs may be provided in such a manner that the secondary coils  22  are connected in series, and the secondary current generated in one of the two secondary coils can be supplied to the other.