JP2008291728A - Igniter for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an igniter both reducing the ON voltage and ensuring power supply start time at the time the battery voltage is lowered without use of a resistance of a high resistance value. <P>SOLUTION: Charge is accumulated in a gate of an IGBT5, based on a constant current formed in a constant current circuit 6. Thereby, the accumulation rate is kept constant so that a gate voltage VG is raised moderately. The power supply start time Δt0 required from start of coil current supply after a threshold voltage Vt reaches the gate voltage VG, to ignition can be made longer. Since the decline rate of the collector voltage of the IGBT5 is made lower so that both end voltages on the secondary coil 8b side are restrained to a low level, the ON voltage of a plug part voltage V2 is made lower. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention controls an ignition device for an internal combustion engine (hereinafter simply referred to as an ignition device) that controls a current flowing in a primary winding of a coil by a semiconductor switching element and controls ignition by a plug connected to the secondary winding of the coil. )).

  In the ignition device, when energization of the ignition coil is started, a positive voltage, so-called on-voltage, is generated in the plug on the secondary winding side of the ignition coil. It is known that there is a fear. Particularly in recent engines, as the compression ratio and lean burn increase, there is a tendency to increase the voltage generated by the ignition coil, so the on-voltage tends to increase. Therefore, the necessity for reducing the on-voltage is increasing.

As a conventional coil driving circuit, for example, the circuit shown in FIG. 6 is known, which includes two resistors 102 and 103 between the gate of the IGBT 100 and the power source 101 and an NPN transistor between the two resistors 102 and 103. 104 is connected, and the NPN transistor 104 is turned on / off by a signal obtained by waveform shaping of the ignition signal from the engine ECU 105 by the waveform shaping circuit 106, whereby current is supplied to the gate of the IGBT 100 and when it is not supplied. It is a circuit configuration that can control. In this circuit, the on-voltage can be reduced by increasing the resistance value of the resistor 102 (see, for example, Patent Document 1).
JP 2001-193615 A

  However, if this resistance value is increased too much, the rate of increase of the gate voltage decreases and the time required to reach the predetermined voltage becomes longer. From when the gate voltage reaches the threshold voltage and the coil current starts to flow until ignition occurs The energization time required for is shortened. As a result, depending on the operating conditions, for example, at a high speed, a predetermined energization time cannot be obtained, and the ignition coil does not generate a desired voltage, which may cause a misfire. Therefore, it is necessary to select the resistance value of the resistor 102 so that both the on-time and the energization start time are ensured, and the degree of freedom of selection is small.

  In recent years, the number of electronic devices installed in vehicles tends to increase and the electric load on the battery tends to increase. Therefore, the amount of decrease in battery voltage tends to increase depending on the driving conditions and the usage conditions of the electronic devices. In particular, such a situation tends to occur at the time of starting. In the case of the circuit of FIG. 6, when the battery voltage decreases, the rate of increase in the gate voltage decreases, and the variation in the energization start time increases, so there is a possibility that a coil current that ensures a predetermined ignition performance cannot flow. is there. In order to prevent this, it is necessary to reduce the resistance value of the resistor 102. However, this increases the on-voltage when the battery voltage is high. As described above, in the conventional circuit, there is a problem that it is very difficult to achieve both reduction of the on-voltage and securing of the energization start time in consideration of a decrease in the battery voltage.

  The present invention has been made in view of the above points, and it is an object of the present invention to provide an ignition device that can achieve both reduction of on-voltage when battery voltage drops and securing of energization start time without using a resistor having a high resistance value. .

  In order to achieve the above object, in the present invention, the primary coil (8a) is connected to the primary winding (8a), and the gate voltage (VG) is controlled to control the current flowing between the collector and the emitter. The coil current (I1) flowing through the winding (8a) is controlled, the voltage (V2) across the secondary winding (8b) of the ignition coil (8) is controlled, and the discharge at the plug (10) is controlled. A semiconductor switching element (5) having a MOS structure and a constant current circuit for accumulating charges in the gate and increasing the gate voltage (VG) by supplying a constant current to the gate of the semiconductor switching element (5) 6) and whether or not the constant current formed by the constant current circuit (6) is supplied to the gate of the semiconductor switching element (5) based on the ignition signal, thereby switching on / off of the semiconductor switching element (5). Is characterized in that it comprises a control the control means (2, 3), the.

In such an ignition device, charges are accumulated in the gate of the semiconductor switching element (5) based on the constant current formed by the constant current circuit (6). For this reason, the rate at which charges are accumulated in the gate can be kept constant, and the rise in the gate voltage (VG) can be moderated. Specifically, the gate voltage (VG) of the semiconductor switching element (5) is linear with a constant gradient when the constant current formed by the constant current circuit (6) is supplied to the gate by the control means (3). Then, the semiconductor switching element (5) becomes flat at the threshold voltage (Vt), and further rises linearly with a constant gradient.
Then, the gate voltage (VG) reaches the threshold voltage (Vt) and the coil current starts to flow. However, when the gate voltage (VG) is near the threshold voltage (Vt), the current of the semiconductor switching element (5). Since the current-carrying capacity is limited, the threshold voltage (Vt) of the semiconductor switching element (5) can take a substantially flat time (Δt0) for a long time. During this time, the collector voltage of the semiconductor switching element (5) Can be reduced, and the potential difference between both ends of the primary winding (8a) can be reduced. As a result, it is possible to suppress the difference in electric current between both ends on the secondary winding (8b) side, so that the on-voltage generated in the electrode portion (V2) of the plug (10) can be reduced.

  For example, by setting the current value of the constant current formed in the constant current circuit (6) to 10 to 200 μA, the time for the flat state can be set to 5 to 200 μs.

  In addition, the code | symbol in the bracket | parenthesis of each said means shows the correspondence with the specific means as described in embodiment mentioned later.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a circuit configuration diagram of an ignition system including an ignition device 1 according to the present embodiment. With reference to this figure, the ignition device 1 in the present embodiment will be described.

  As shown in FIG. 1, the ignition device 1 includes a waveform shaping circuit 2, an NPN transistor 3, a resistor 4, an IGBT 5, and a constant current circuit 6, and is based on an ignition signal from the engine ECU 7. Then, switching control of power supply from the power source 9 to the primary winding 8a of the ignition coil 8 is performed.

  The ignition signal sent from the engine ECU 7 is shaped by the waveform shaping circuit 2, and the NPN transistor 3 is controlled by controlling the gate voltage of the NPN transistor 3 by the signal after waveform shaping. Specifically, when an ignition signal is sent from the engine ECU 7 that is at a low level before energization of the coil and at a high level when the coil is energized, the level is inverted by the waveform shaping circuit, and the inverted ignition signal is Thus, ON / OFF of the NPN transistor 3 is controlled.

  The collector of the NPN transistor 3 is connected to the gate of the IGBT 5 through the input protection resistor 4, and the gate voltage VG applied to the gate of the IGBT 5 is controlled according to the ON / OFF state of the NPN transistor 3. The That is, when the NPN transistor 3 is turned on, the collector potential of the NPN transistor 3 (that is, the gate voltage of the IGBT 5) becomes almost zero, so that the IGBT 5 is turned off. Turn on to become. For this reason, when the IGBT 5 is off, no current flows through the primary winding 8a of the ignition coil 8 connected to the collector of the IGBT 5, and no potential difference occurs between both ends of the primary winding 8a. Although no potential difference is generated, when the IGBT 5 is turned on, a current flows through the primary winding 8a of the ignition coil 8 based on the power supply from the power source 9 such as a battery, and a potential difference is generated across the primary winding 8a. As a result, a potential difference that is twice the turn ratio of the primary winding 8a and the secondary winding 8b is generated at both ends of the secondary winding 8b. In the process of turning off the IGBT 5 after a desired current is passed through the primary winding, the collector voltage of the IGBT 5 rises, causing a voltage difference in the primary winding 8a, and the primary winding 8a also in the secondary winding 8b. And a high voltage that is twice the turn ratio of the secondary winding 8b is generated. Thus, since the plug 10 connected to the secondary winding 8b of the ignition coil 8 can be discharged, the ignition timing of the plug 10 can be controlled by the ignition device 1 based on the ignition signal of the engine ECU 7. It can be done.

  In the ignition device 1 having such a structure, the constant current circuit 6 is disposed on a path for supplying the gate voltage VG from the power source 9 to the gate of the IGBT 5. When the NPN transistor 3 is turned off, charges are accumulated in the gate of the IGBT 5 based on the constant current formed by the constant current circuit 6. As a result, the gate voltage VG rises and the IGBT 5 is turned on. As the constant current circuit 6, for example, one having a constant current value of 10 to 200 μA can be used.

  As described above, the ignition device 1 of the present embodiment is configured. Next, detailed operations and effects of the ignition device 1 of the present embodiment will be described with reference to FIGS.

  FIG. 2 is a timing chart of each part at the time of ignition by the ignition device 1 of the present embodiment, and FIG. 3 is a timing chart showing only the change in the gate voltage of the IGBT 5 in the period TA shown in FIG. .

  As shown in FIG. 2, an ignition signal is input from the engine ECU 7. First, when the ignition signal is at a low level, the waveform shaping circuit 2 inverts it to a high level signal, so that the NPN transistor 3 is turned on. For this reason, the potential difference between the collector and the emitter of the NPN transistor 3 becomes almost zero, the constant current formed by the constant current circuit 6 flows to the NPN transistor 3 side, and the IGBT 5 is turned off.

  On the other hand, when the ignition signal is switched from the Low level to the Hi level at the time T1 in the figure, the ignition signal is inverted to the Low level by the waveform shaping circuit 2, so that the NPN transistor 3 is turned off. Thereby, charges are accumulated in the gate of the IGBT 5 through the resistor 4 based on the constant current formed by the constant current circuit 6. At this time, since the current is limited by the constant current formed by the constant current circuit 6, the rate at which charges are accumulated in the gate of the IGBT 5 is kept constant. Since the gate of the IGBT 5 has an input capacity and the gate voltage VG does not increase unless a certain amount of charge is supplied, the gate voltage depends on the charging time of the input capacity of the gate of the IGBT 5. The increase in VG can be moderated. Therefore, as shown in FIG. 3, the gate voltage VG rises at the first linear gradient θ1 that is relatively gentle to the threshold voltage Vt of the IGBT 5.

  Then, when a certain amount of electric charge is accumulated in the IGBT 5 and the gate voltage VG reaches the threshold voltage Vt as shown at time T2 in FIGS. 2 and 3, the IGBT 5 is switched from OFF to ON. Thereby, the collector voltage VC of the IGBT 5 is lowered, a potential difference is generated between both ends of the primary winding 8a, and energization to the primary winding 8a of the ignition coil 8 is started. Accordingly, as shown in FIG. 2, the voltage across the secondary winding 8b becomes a high voltage corresponding to the winding ratio with the primary winding 8a, and an on-voltage is generated in the plug portion voltage V2.

  However, although the gate voltage VG reaches the threshold voltage Vt and the coil current starts to flow, the current conduction capability of the IGBT 5 is limited when the gate voltage VG is in the vicinity of the threshold voltage Vt. The collector voltage VC of the IGBT 5 starts to gradually decrease from the voltage VB of the power source 9. During the time when the collector voltage VC decreases, the current supplied to the gate is charged according to the capacitance between the collector and the gate and the voltage change therebetween, so as shown in FIGS. 2 and 3, the gate voltage VG Remains substantially flat at the threshold voltage Vt. The time for the flat state is also determined by the magnitude of the constant current formed by the constant current circuit 6, and can be a fixed time. For example, when the current value of the constant current formed by the constant current circuit 6 is set to 10 to 200 μA as described above, the time for the flat state can be set to 5 to 200 μsec.

  Thereafter, when the collector voltage VC of the IGBT 5 is lowered, a certain amount of charge is accumulated in the gate of the IGBT 5, so that the coil current is limited by limiting the current capability of the IGBT 5, that is, the current flowing through the primary winding 8a is limited. The gate voltage VG rises again linearly at the first gradient θ1. In the process of turning off the IGBT 5 after a desired current is passed through the primary winding, the collector voltage of the IGBT 5 rises, causing a voltage difference in the primary winding 8a, and the primary winding 8a also in the secondary winding 8b. And a high voltage that is twice the turn ratio of the secondary winding 8b is generated. Thereby, the plug 10 connected to the secondary winding 8b of the ignition coil 8 is discharged, and ignition is performed.

  In this way, by accumulating charges in the gate of the IGBT 5 based on the constant current formed by the constant current circuit 6, the accumulation speed can be kept constant, and the gate voltage VG can be kept constant. It is possible to moderate the rise. Then, the current limit time Δt0 during which the current limit by the IGBT is applied after the gate voltage VG reaches the threshold voltage Vt and the coil current starts to flow is determined by the time during which the gate voltage is constant at the threshold voltage Vt, These can be determined by the magnitude of the constant current formed by the constant current circuit 6. For this reason, this energization start time Δt0 can be adjusted, and the speed of the decrease in the collector voltage of the IGBT 5 can be adjusted. As a result, the energization start time Δt0 can take a long time, and the voltage at both ends on the secondary winding 8b side can be kept low by slowing down the collector voltage drop of the IGBT 5, so that the plug portion It becomes possible to reduce the ON voltage of the voltage V2.

  Further, even when the voltage of the power source 9 rises or falls, as shown by the broken line in FIG. 3, the way of changing the gate voltage VG is almost the same as the normal voltage of the power source 9, and the power source Regardless of the voltage of 9, the current limit time Δt0 is substantially constant. Therefore, even if the voltage of the power supply 9 fluctuates, the on-voltage can be lowered.

  FIG. 4 is a timing chart of each part at the time of ignition by the conventional ignition device, and FIG. 5 is a timing chart showing only the change in the gate voltage of the IGBT in the period TA shown in FIG. ) To (c) show the power supply (battery) voltage when it is normal, when it rises, and when it falls.

  Also in the case of the conventional ignition device, when the ignition signal is switched from the Low level to the Hi level at time T1 in FIG. 4, charges are accumulated in the gate of the IGBT 100 via the resistors 102 and 103 shown in FIG. At this time, since the current is supplied to the gate of the IGBT 100 via the resistors 102 and 103, the gate voltage VG reaches the threshold voltage Vt as shown in FIGS. The initial period of rising and the rising period higher than the threshold voltage Vt also show an exponential curve according to the time constant of the charging circuit of the resistors 102 and 103 and the capacitor composed of the gate capacitance, and the gradient θ2 is also large. The threshold voltage Vt is flat for a short period. For this reason, as shown in FIG. 4, the gate voltage VG increases rapidly, the collector voltage VC decreases rapidly, and the voltage V2 across the secondary winding becomes higher than necessary. turn into.

  Here, in the conventional ignition device, when the power source is in a normal state (for example, battery voltage ≈ 12 V), for example, the resistance value of the resistor 102 and the gate insulating film thickness are set to reduce the on-voltage to the same level as in the present embodiment. By adjusting the time of the portion where the waveform of the gate voltage VG is in a flat state by adjusting the voltage, the change time of the collector voltage VC can be adjusted as in the present embodiment. It is possible to suppress an increase in the voltage at both ends, and it is also possible to suppress an on-voltage determined by the voltage across the secondary winding.

  However, as shown in FIGS. 5A to 5C, the manner of changing the gate voltage VG in the conventional ignition device differs depending on the magnitude of the power supply voltage. When the power supply voltage becomes larger than normal, the gate voltage VG changes. The voltage VG rises quickly (gradient θ2 is larger), and when the power supply voltage is smaller than normal, the gate voltage VG is delayed (gradient θ2 is reduced). For this reason, the current limit time Δt0 varies greatly depending on the magnitude of the power supply voltage, and there is a possibility that the ignition coil cannot be energized when the power supply voltage decreases.

  As described above, according to the ignition device 1 of the present embodiment, the on-voltage is lowered by causing the charge to be accumulated in the gate of the IGBT 5 based on the constant current formed by the constant current circuit 6. And securing the current limit time Δt0 are possible. Further, since a constant current circuit 6 is used instead of a resistor having a high resistance value, the degree of freedom in selection does not decrease.

  Furthermore, since the constant current circuit 6 is used, the current limit time Δt0 can be made substantially constant even when the voltage of the power source 9 fluctuates. Therefore, it is possible to make the ignition device 1 of the present embodiment less affected by the voltage drop of the power source 9 as when the battery voltage drops, for example.

  Although an on-fire prevention diode can be provided between the primary winding 8a and the secondary winding 8b of the ignition coil 8, as described above, according to the ignition device 1 of the present embodiment, the Since the voltage can be reduced, this diode may not be provided. Of course, if an on-fire prevention diode is provided, on-fire prevention can be more reliably prevented.

(Other embodiments)
In the above embodiment, the IGBT 5 has been described as an example of a semiconductor switching element for driving a load. However, the present invention can be applied even when a power MOSFET is used.

  Further, in the above embodiment, the waveform shaping circuit 2 and the NPN transistor 3 are used as control means for controlling whether or not the constant current formed by the constant current circuit 6 is supplied to the gate of the IGBT 5 based on the ignition signal. However, other circuit configurations may be used. For example, the NPN transistor 3 may be changed to a MOS transistor.

It is a circuit block diagram of the ignition system containing the ignition device in 1st Embodiment of this invention. It is a timing chart of each part at the time of ignition by the ignition device shown in FIG. 3 is an enlarged timing chart showing only the change in the gate voltage of the IGBT 5 during the period TA shown in FIG. It is a timing chart of each part at the time of ignition by the conventional ignition device. 5 is an enlarged timing chart showing only the change in the gate voltage of the IGBT in the period TA shown in FIG. 4, and (a) to (c) show when the power supply (battery) voltage is normal, when it rises, and when it falls. It is the timing chart shown. It is a circuit block diagram of the ignition system containing the conventional ignition device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Ignition device, 2 ... Waveform shaping circuit, 3 ... NPN transistor, 4 ... Resistance,
5 ... IGBT, 6 ... constant current circuit, 7 ... engine ECU, 8 ... ignition coil,
8a ... primary winding, 8b ... secondary winding, 9 ... power supply, 10 ... plug

Claims (4)

Coil current that is connected to the primary winding (8a) of the ignition coil (8) and controls the gate voltage (VG) to control the current that flows between the collector and the emitter, thereby flowing the primary winding (8a). (I1) is controlled, and the voltage (V2) across the secondary winding (8b) of the ignition coil (8) is controlled to control the discharge at the plug (10). )When,
A constant current circuit (6) for storing a charge in the gate and increasing the gate voltage (VG) by supplying a constant current to the gate of the semiconductor switching element (5);
By switching whether or not to supply the constant current formed by the constant current circuit (6) to the gate of the semiconductor switching element (5) based on the ignition signal, the semiconductor switching element (5) And an ignition device for an internal combustion engine, characterized by comprising control means (2, 3) for controlling on / off. The gate voltage (VG) of the semiconductor switching element (5) has a constant gradient when the constant current formed by the constant current circuit (6) is supplied to the gate by the control means (3). 2. The method according to claim 1, wherein after rising linearly, the semiconductor switching element (5) becomes flat at the threshold voltage (Vt) and further rises linearly with a constant gradient. The ignition device for internal combustion engines as described. The internal combustion engine ignition device according to claim 2, wherein the time for the flat state is 5 to 200 μs. The ignition device for an internal combustion engine according to any one of claims 1 to 3, wherein a current value of the constant current formed by the constant current circuit (6) is 10 to 200 µA.

Images