Abstract:
The ignition apparatus includes an electronic control unit and an igniter. The igniter detects ions resulting from ignition, and sends an ion current output signal to the electronic control unit. The igniter has a waveform shaping circuit and an ion current detecting/outputting circuit. The waveform shaping circuit is adapted such that a voltage at an input terminal thereof becomes higher than a predetermined reference voltage to turn the switching element ON when the ignition signal is caused to flow through an electric load. The ion current detecting/outputting circuit has an output terminal which is connected to the input terminal and outputs therefrom an ion current output signal obtained as a result of conversion of an ion current, and is adjusted such that the voltage at the input terminal at the time when the ion current output signal is outputted to the electronic control unit becomes lower than the reference voltage.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an ignition apparatus for an internal combustion engine mounted in, for example, an automobile, and more particularly to an ignition apparatus for an internal combustion engine in which a high voltage for ignition is generated in a secondary coil of an ignition coil by allowing and shutting off a flow of a current to a primary coil of the ignition coil by means of a switching element. 
   2. Description of the Related Art 
   A conventional ignition apparatus for an internal combustion engine is provided with resistors through which a current corresponding to an ion current and a current of an ignition signal are caused to flow, respectively, a comparator for comparing voltages generated in the resistors with each other, and a switch for making a switchover between the current of the ignition signal and the current corresponding to the ion current based on a result of the comparison, with a view to outputting an output from a circuit for detecting an ion current via the same route as is followed by the ignition signal (e.g., see JP 2004-156608 A). 
   However, this ignition apparatus is susceptible to an influence of a discrepancy in characteristics between the resistor configured on a coil side and the resistor for supplying the ignition signal and the influence of the potential of a ground GND, thereby causing problems in that the ignition signal cannot be supplied to a switching element with accuracy and that the size of the circuit is increased. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide an ignition apparatus for an internal combustion engine which allows an ignition signal and an ion current output signal to be transmitted through a single signal line and prevents erroneous ignition from being caused even if disturbances are added to those signals during transmission thereof. 
   According to the present invention, an ignition apparatus for an internal combustion engine, includes: an electronic control unit for outputting an ignition signal for controlling an ignition timing; an igniter for allowing and shutting off flow of a current to a primary coil of an ignition coil by means of a switching element based on the ignition signal from the electronic control unit to thereby cause a high voltage for ignition to be generated in a secondary coil of the ignition coil, taking out ions, which are produced in an ignition plug as a result of ignition, as an ion current through application of a bias voltage, converting the ion current into an ion current output signal, and outputting the ion current output signal to the electronic control unit; and a signal line for allowing both the ignition signal and the ion current output signal to be transmitted therethrough. In the ignition apparatus, the igniter includes: a waveform shaping circuit having an input terminal to which the signal line is connected and an electric load is also connected in parallel, for being adapted such that a voltage at the input terminal rises above a predetermined reference voltage to turn the switching element ON when the ignition signal is caused to flow through the electric load; and an ion current detecting/outputting circuit having an output terminal connected to the input terminal to output therefrom the ion current output signal obtained as a result of conversion of the ion current, for being adjusted such that the voltage at the input terminal at a time when the ion current output signal is outputted to the electronic control unit becomes lower than the reference voltage. 
   In the ignition apparatus for the internal combustion engine according to the present invention, an ignition signal and an ion current output signal are transmitted through the single signal line, and there is set a difference between a voltage resulting from the ignition signal and a voltage resulting from the ion current output signal such that the switching element for generating a high voltage for ignition in the ignition plug is held OFF when the ion current output signal is transmitted. Thus, the ignition apparatus achieves an effect of preventing the size of the circuit from being increased. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings: 
       FIG. 1  is a circuit diagram of an ignition apparatus for an internal combustion engine according to a first embodiment of the present invention; 
       FIG. 2  shows timing charts of signals at respective portions of the ignition apparatus for the internal combustion engine according to the first embodiment of the present invention; 
       FIG. 3  is a circuit diagram of an ion current detecting/outputting circuit according to a second embodiment of the present invention; 
       FIG. 4  is a circuit diagram of an ignition apparatus for an internal combustion engine according to a third embodiment of the present invention; and 
       FIG. 5  is a circuit diagram of an ignition apparatus for an internal combustion engine according to a fourth embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   First Embodiment 
     FIG. 1  is a circuit diagram of an ignition apparatus for an internal combustion engine according to a first embodiment of the present invention.  FIG. 2  shows timing charts of signals at respective portions of the ignition apparatus for the internal combustion engine according to the first embodiment of the present invention. 
   An ignition apparatus  1  for an internal combustion engine (hereinafter referred to simply as the “ignition apparatus  1 ”) according to the first embodiment of the present invention is designed as an ignition apparatus for an internal combustion engine mounted in an automobile. As shown in  FIG. 1 , the ignition apparatus  1  is composed of an electronic control unit  2  (hereinafter referred to as the “ECU  2 ”) and an igniter  3 . 
   The ECU  2  has a processing unit  4 , an ignition signal driving circuit  5 , and an ion control circuit  6 . 
   The processing unit  4  sends out an ignition command signal IGt 1  at a desired timing, for example, at a time point t 1  based on a signal from a sensor (not shown) or the like, and analyzes an ion current output signal inputted after ignition. 
   In the ignition signal driving circuit  5 , a transistor  25  is turned ON when the ignition command signal IGt 1  inputted to a base of the transistor  25  becomes low in level, so an ignition signal current flows from a power supply  26  to a ground GND via the transistor  25 , a signal line  7 , and an input resistor  9 . 
   The ion control circuit  6  sends to the processing unit  4  only an ion current output signal transmitted from the igniter  3  via the signal line  7 . 
   The ion control circuit  6  is composed of a current mirror circuit  43  and a transistor  44  having a push-pull circuitry. The current mirror circuit  43  is composed of transistors  41  and  42 . A collector of the transistor  41  is connected to a collector of the transistor  42  and a positive input terminal of a comparator circuit  16  of a waveform shaping circuit  10 . An emitter of the transistor  41  is connected to an emitter of the transistor  42  and a collector of the transistor  44 . A base of the transistor  44  is connected to a terminal for outputting an ignition command signal of the processing unit  4 . An emitter of the transistor  44  is connected to the ground GND. 
   The transistor  44  is turned OFF when the ignition command signal IGt 1  becomes low in level, and is turned ON when the ignition command signal IGt 1  becomes high in level. While a switching element  11  is ON, that is, while the ignition command signal IGt 1  is low in level, the transistor  44  is OFF. Therefore, an ignition signal IGt is not transmitted to the processing unit  4  as an ion current output signal, so the transistor  44  functions as a mask circuit. 
   The igniter  3  is composed of an ignition coil  8 , the input resistor  9  as an electric load, the waveform shaping circuit  10 , the switching element  11 , an ion biasing circuit  12 , and an ion current detecting/outputting circuit  13 . 
   The waveform shaping circuit  10 , which has a reference voltage source  15  and the comparator circuit  16 , drives the switching element  11  by means of the ignition signal IGt from the ignition signal driving circuit  5 . The signal line  7  is connected to the positive input terminal of the comparator circuit  16 , and the reference voltage source  15  is connected to a negative input terminal of the comparator circuit  16 . An output terminal of the comparator circuit  16  is connected to a gate of the switching element  11 . 
   When the voltage inputted from the positive input terminal exceeds a reference voltage Vton of the reference voltage source  15 , the voltage at the output terminal of the comparator circuit  16  changes in level from low to high. 
   The switching element  11  is, for example, an insulated gate bipolar transistor (IGBT) having a gate terminal G, a collector terminal C, and an emitter terminal E. The output terminal of the comparator circuit  16  is connected to the gate terminal G. A primary coil  17  of the ignition coil  8  is connected to the collector terminal C. The emitter terminal E is connected to the ground GND as a reference potential point of a body of an automobile or the like. In general, this reference potential point is referred to as an earth. 
   The ignition coil  8  has the primary coil  17  and the secondary coil  18 . An output terminal of an on-vehicle battery or the like is connected to a power supply terminal V B , to which the primary coil  17  is connected. The direct-current voltage at the output terminal of the on-vehicle battery is, for example, 12 V, and the voltage at the power supply terminal V B  is 12 V. 
   An ignition plug  19  is connected to a high-voltage side  18   a  of the secondary coil  18 . The ignition plug  19  is disposed in a combustion chamber of the internal combustion engine so as to ignite and burn a fuel such as gasoline which is supplied into the combustion chamber. 
   An input terminal  12   a  of the ion biasing circuit  12  is connected to a low-voltage side  18   b  of the secondary coil  18 . 
   The ion biasing circuit  12  is provided with two terminals, that is, the input terminal  12   a  and an output terminal  12   b . The output terminal  12   b  is connected to the ion current detecting/outputting circuit  13  disposed at a stage subsequent thereto. The input terminal  12   a  is connected to the low-voltage side  18   b  of the secondary coil  18 . 
   An internal configuration of the ion biasing circuit  12  will now be described. The ion biasing circuit  12  has a diode  21 , a resistor  22 , a Zener diode  23 , and a capacitor  24 . An anode of the diode  21  and one terminal of the resistor  22  are connected to the low-voltage side  18   b  of the secondary coil  18 . A cathode of the diode  21  and the other terminal of the resistor  22  are connected to a cathode of the Zener diode  23  and one terminal of the capacitor  24 , respectively. An anode of the Zener diode  23  and the other terminal of the capacitor  24  are connected to the output terminal  12   b.    
   The diode  21  suppresses a secondary voltage generated in the secondary coil  18  when a primary current rises in the primary coil  17 , thereby preventing erroneous ignition. The resistor  22  secures a path through which an ion current flows. Due to the voltage generated at the high-voltage side  18   a  of the secondary coil  18 , the Zener diode  23  and the capacitor  24  are charged with electric charges. 
   The ion current detecting/outputting circuit  13  is provided with two terminals, that is, an input terminal  13   a  and an output terminal  13   b . The input terminal  13   a  is connected to the output terminal  12   b  of the ion biasing circuit  12 . The output terminal  13   b  is connected to the signal line  7  at a location closer to the ECU  2  than a junction point of the input resistor  9 . 
   An internal structure of the ion current detecting/outputting circuit  13  will now be described. The ion current detecting/outputting circuit  13  has two diodes  31  and  32 , a current mirror circuit  35  including two transistors  33  and  34 , and a resistor  36 . An anode of the diode  31  and a cathode of the diode  32  are connected together, and a cathode of the diode  31  and an anode of the diode  32  are connected together, so a bidirectional diode is constituted. The anode of the diode  31  is connected to the input terminal  13   a , and the cathode of the diode  31  is grounded. 
   An emitter of the transistor  33  and an emitter of the transistor  34  in the current mirror circuit  35  are connected to an internal power supply V CC . A base of the transistor  33  is connected to a base of the transistor  34  and a collector of the transistor  33 . The collector of the transistor  33  is connected to the input terminal  13   a . On the other hand, a collector of the transistor  34  is connected to the output terminal  13   b  via the resistor  36 . 
   Next, an operation of the ignition apparatus  1  will be described with reference to  FIG. 2 . 
   The ignition command signal IGt 1  is inputted to the ignition signal driving circuit  5  from the processing unit  4  at the time point t 1 , and the ignition signal driving circuit  5  is turned ON, so an ignition signal current flows through the input resistor  9 . When the ignition signal current flows through the input resistor  9 , a voltage Vout of the signal line  7  rises. When the voltage Vout at the positive input terminal of the comparator circuit  16  becomes equal to or higher than the reference voltage Vton set in the reference voltage source  15 , the switching element  11  is turned ON. As a result, a primary current I 1  is caused to flow through the primary coil  17 . 
   After that, when the voltage Vout at the positive input terminal of the comparator circuit  16  falls below the reference voltage Vton at a time point t 2 , the switching element  11  is turned OFF. The ignition command signal IGt 1  becomes high in level after the time point t 2 , so the transistor  44  of the ion control circuit  6  is turned ON. 
   At the moment when the switching element  11  is turned OFF, the primary current I 1  flowing through the primary coil  17  is shut off, and a high-voltage is generated in the collector C of the switching element  11 . 
   This high voltage is converted into a negative voltage capable of insulating and destroying a gap of the ignition plug  19 , and applied to the secondary coil  18 . Then, at a time point t 3  when the gap of the ignition plug  19  is insulated and destroyed, a secondary current I 2  flows from the ignition plug  19  side to the secondary coil  18  and then to the ground GND via the diode  21 , the Zener diode  23 , and the diode  31 . 
   After that, at a time point t 4  when discharge is terminated, a voltage generated due to the electric charges with which the capacitor  24  is charged is biased in the gap of the ignition plug  19  and applied to ions generated as a result of combustion in a cylinder. An ion current thereby flows to the secondary coil  18  via the resistor  22 . The transistor  33  is turned ON at this moment, so the current mirror circuit  35  is operated. 
   Since the transistor  44  is ON, the transistor  34  of the current mirror circuit  35  supplies a collector current corresponding to an iron current, which has flown via the transistor  33 , to the ion control circuit  6  in the ECU  2 . 
   When a current corresponding to an ion current flows through the transistor  42  of the current mirror circuit  43 , it flows then to the transistor  41 . The current corresponding to the ion current flows to the processing unit  4 . This current corresponding to the ion current is an ion current output signal. 
   It should be noted that the voltage at the positive input terminal of the comparator circuit  16  is obtained by subtracting a voltage between the collector and the emitter of the transistor  34  and a fall in voltage at the resistor  36  from a voltage of the internal power supply V CC  in a time zone in which the ion current flows. By setting the voltage at the positive input terminal of the comparator circuit  16  lower than the reference voltage Vton, the current corresponding to the ion current can be caused to flow through the signal line  7  while the output of the comparator circuit  16  is held low. 
   The ignition apparatus  1  as described above can cause a current corresponding to an iron current to flow through the common signal line  7  without allowing the output of the comparator circuit  16  to become high in level or allowing a high voltage to be applied to the ignition plug  19 , thereby making it possible to prevent the size of the circuit from being increased. 
   The current mirror circuit  35  is configured in the ion current detecting/outputting circuit  13 , and a current corresponding to an ion current is caused to flow through the ion control circuit  6 . Therefore, unlike the case of a voltage, stable control can be performed without being influenced by fluctuations in the potential at the ground GND. 
   The ion control circuit  6  is provided with the transistor  44 , which is OFF when an ignition signal is sent thereto, so the ion control circuit  6  is OFF when the ignition signal is sent thereto. Therefore, the ignition signal can be reliably transmitted to the comparator circuit  16  and the components subsequent thereto. As a result, an improvement in reliability can be achieved. 
   The transistor  25 , which is turned ON when the ignition command signal is low in level, and the transistor  44 , which is turned ON when the ignition command signal is high in level, are configured as the push-pull circuit. Therefore, the configuration of a circuit for separating an ignition signal from an ion current output signal can be simplified. 
   Second Embodiment 
     FIG. 3  is a circuit diagram of an ion current detecting/outputting circuit  13 B according to a second embodiment of the present invention. 
   As shown in  FIG. 3 , the ion current detecting/outputting circuit  13 B according to the second embodiment of the present invention is different from the ion current detecting/outputting circuit  13  according to the first embodiment of the present invention in that a group of a plurality of transistors  34 B is employed instead of the transistor  34 , and in that a base current compensating transistor  37  for compensating for a base current flowing through the group of the transistors  34 B is added. Since they are identical in other respects, the same description will be omitted by allocating like reference symbols to like components. 
   An emitter of the base current compensating transistor  37  is connected to a base of the transistor  33 , a base of the base current compensating transistor  37  is connected to a collector of the transistor  33 , and the collector of the base current compensating transistor  37  is connected to the ground GND. 
   The ignition apparatus for an internal combustion engine as described above compensates for a base current flowing through the group of the transistors  34 B by means of the base current compensating transistor  37 , thereby making it possible to amplify a current corresponding to an ion current by means of the group of the transistors  34 B and cause the amplified current to flow through the ion control circuit  6 . As a result, such an amount of current as to tolerate disturbances can be ensured, so more stable control can be performed. 
   Third Embodiment 
     FIG. 4  is a circuit diagram of an ignition apparatus  1 C for an internal combustion engine (hereinafter referred to simply as the “ignition apparatus  1 C”) according to a third embodiment of the present invention. 
   As shown in  FIG. 4 , the ignition apparatus  1 C according to the third embodiment of the present invention is different from the ignition apparatus  1  according to the first embodiment of the present invention in that a power supply circuit  50  is added, and in that an ion current detecting/outputting circuit  13 C and a first constant current circuit  14  as an electric load are employed instead of the ion current detecting/outputting circuit  13  and the input resistor  9 , respectively. Since they are identical in other respects, the same description will be omitted by allocating like reference symbols to like components. 
   The first constant current circuit  14  causes a constant current to flow from the power supply  26  to the transistor  25  and the signal line  7  when the transistor  25  in the ignition signal driving circuit  5  is turned ON. 
   While the ion current detecting/outputting circuit  13  is provided with the internal power supply V CC  in the first embodiment of the present invention, the power supply circuit  50 , which generates the internal power supply V CC  from a power supply V B  supplied with power from a battery, is provided in the third embodiment of the present invention. 
   The power supply circuit  50  has two resistors  51  and  52 , a transistor  53 , and a clamping diode  54 . One terminal of the resistor  51  is connected to the power supply V B , and the other terminal of the resistor  51  is connected to an emitter of the transistor  53  and one terminal of the resistor  52 . The other terminal of the resistor  52  is connected to a base of the transistor  53  and a cathode of the clamping diode  54 . An anode of the clamping diode  54  is connected to the ground GND. A collector of the transistor  53  is connected to the emitter of the transistor  34  in the ion current detecting/outputting circuit  13 C. The voltage at the collector of the transistor  53  is equal to the voltage of the internal power supply V CC . 
   The ion current detecting/outputting circuit  13 C according to the third embodiment of the present invention is obtained by adding a second constant current circuit  38  and a transistor  39  to the ion current detecting/outputting circuit  13  according to the first embodiment of the present invention. The second constant current circuit  38  is interposed between the internal power supply V CC  and an emitter of the base current compensating transistor  37 . A base of the transistor  39  is connected between the collector of the transistor  34  and the resistor  36 . A collector of the transistor  39  is connected to the output terminal  13   b.    
   Next, an operation of the ignition apparatus  1 C according to the third embodiment of the present invention will be described. However, the description of the operation will be limited to what is different from the first embodiment of the present invention without making reference to what is similar thereto. 
   When the ignition command signal IGt 1  becomes low in level and supplied to the base of the transistor  25 , a current of the ignition signal IGt flows from the power supply  26  to the ground GND via the transistor  25  and the first constant current circuit  14 . 
   When an ion current flows, a current corresponding to the ion current flows from the internal power supply V CC  to the output terminal  13   b  via the transistor  34  and the resistor  36 , and a constant current flows from the internal power supply V CC  to the output terminal  13   b  via the second constant current circuit  38  and the transistor  39 . The current corresponding to the ion current and the constant current are then superimposed on each other at the output terminal  13   b . A component of a resultant current which corresponds to the constant current flows to the ground GND via the first constant current circuit  14 , and the current corresponding to the ion current flows to the ground GND via the transistors  42  and  44 . 
   By thus equalizing the intensity of the constant current flowing through the second constant current circuit  38  with the intensity of the constant current flowing through the first constant current circuit  14 , only the current corresponding to the ion current can be supplied to the ion control circuit  6 . 
   Since the power supply circuit  50  is equipped with a clamping circuit, the voltage generated at the time when a current corresponding to an ion current flows is suppressed. Therefore, by setting the voltage of the internal power supply V CC  equal to or lower than the reference voltage Vton of the waveform shaping circuit  10 , the current corresponding to the ion current can be supplied to the ECU  2  side without turning the waveform shaping circuit  100 N. 
   In the ignition apparatus  1 C as described above, the first constant current circuit  14  is connected to the positive input terminal of the waveform shaping circuit  10  to cause a constant current to flow through the signal line  7  as an ignition signal. Thus, the reliability of electric contact pertaining to, for example, a connector of the signal line  7  for connecting the ECU  2  to the igniter  3  can be enhanced. 
   When a current corresponding to an ion current is caused to flow, the same current as the current flowing through the first constant current circuit  14  is outputted from the second constant current circuit  38  in a superimposed manner, so only the current corresponding to the ion current can be supplied to the ion control circuit  6 . As a result, the configuration of the circuit for separating the current corresponding to the ion current can be simplified. 
   Since the power supply circuit  50  is equipped with the clamping circuit, it is possible to ensure a margin for an erroneous operation in detecting and outputting an ion current. Consequently, the power supply circuit  50  is unsusceptible to the influence of disturbances. 
   Fourth Embodiment 
     FIG. 5  is a circuit diagram of an ignition apparatus  1 D for an internal combustion engine (hereinafter referred to simply as the “ignition apparatus  1 D”) according to a fourth embodiment of the present invention. 
   The ignition apparatus  1 D according to the fourth embodiment of the present invention is different from the ignition apparatus  1  according to the first embodiment of the present invention in that an ion current detecting/outputting circuit  13 D is employed and in that the input resistor  9  is omitted. Since they are identical in other respects, the same description will be omitted by allocating like reference symbols to like components. 
   The ion current detecting/outputting circuit  13 D according to the fourth embodiment of the present invention is different from the ion current detecting/outputting circuit  13  according to the first embodiment of the present invention in that a resistor  56  and a diode  57  are connected between the emitter and the collector of the transistor  34 . Since they are identical in other respects, the same description will be omitted by allocating like reference symbols to like components. 
   When the ignition command signal IGt 1  becomes low in level, the transistor  25  is turned ON, and an ignition signal current flows from the power supply  26  via the transistor  25 , the signal line  7 , the diode  57 , and the resistor  56 . The voltage Vout at the positive input terminal of the comparator circuit  16  at this moment is equal to a value obtained by adding a fall in voltage at the resistor  56  to the voltage of the internal power supply V CC . If a circuit constant is set on the assumption that this value is equal to or higher than the reference voltage Vton, the output of the comparator circuit  16  becomes high in level when the ignition signal current flows therethrough. On the other hand, when the ignition command signal IGt 1  is high in level, no current flows through the diode  57  as a reverse bias because the potential of the collector of the transistor  25  is lower than the voltage of the internal power supply V CC . A current corresponding to an ion current flows from the internal power supply V CC  to the ground GND via the transistor  34 , the transistor  42 , and the transistor  44  only when the ion current flows through the transistor  33 . 
   The ignition apparatus  1 D as described above can ensure the reliability of contact pertaining to, for example, the connector of the signal line  7  for connecting the ECU  2  to the igniter  3  by causing an ignition signal current to flow from the power supply  26  to the internal power supply V CC . 
   Since the input resistor  9  and the resistor  36  can be omitted, the circuit can be simplified. 
   In the fourth embodiment of the present invention, the transistor  34  of the ion current detecting/outputting circuit  13 D is constructed as a single transistor. However, a similar effect is achieved even if a group of multiple transistors and a base current compensating transistor are employed as in the case of the second embodiment of the present invention. 
   In the foregoing description, the ignition apparatus according to any one of the first to fourth embodiments of the present invention is utilized as an ignition apparatus for an internal combustion engine mounted in an automobile. However, the ignition apparatus can also be utilized for an internal combustion engine mounted in a ship or an internal combustion engine employed as a mover for domestic or agricultural purposes.