JPH0364711B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an ignition device, and in particular to an ignition device for an internal combustion engine equipped with a DC-DC converter [Prior Art] As a prior art, for example, Japanese Patent Laid-Open No. There is an "internal combustion engine ignition device" shown in Publication No. 165667.

A conventional ignition device using a DC-DC converter has a configuration as shown in FIG. That is,
In the figure, 1 is the battery, 2 is the key switch,
4 is an ignition coil. 3 is an IC igniter which switches the primary current _I1 of the primary coil of the ignition coil 4 to generate a high voltage (secondary voltage) _V2 of 30 to 40 KV in the secondary coil. 3a is a pick-up coil for detecting ignition timing. 5 is a power distributor, and 6 to 9 are spark plugs. 19 is a DC-DC converter which is a medium-high voltage power supply and generates a voltage of approximately 2KV. 10 is an oscillation circuit, 11 is a power transistor, 12 is a transformer, 13 to 16 are rectifying diodes, 17 is a capacitor, and 18a to 18f are high voltage cords. In FIG. 1, the oscillation frequency of the oscillation circuit 10 and the duty of the power transistor 11 (ON time x
100/period (%)) is fixed at an appropriate value.

According to the ignition device shown in Figure 1, it is possible to obtain several times the discharge energy compared to the 20 to 40 mJ of discharge energy of a general ignition device, and it is possible to greatly improve the combustion efficiency of an internal combustion engine. .

However, in the circuit shown in Figure 1, the battery voltage
There is a drawback that the output voltage of the DC-DC converter 19 fluctuates widely due to fluctuations in _VB .

For example, the oscillation frequency and duty ratio of the oscillation circuit 10 are set so that the output voltage V _D2 of _the DC-DC converter 19 (terminal voltage on the secondary coil side of the ignition coil 4 of the capacitor 17) can be generated at about -2 KV when V B = 6 V. When V _B = 16 V, the primary current I _D1 of the primary coil of the transformer 12 increases, so when V _B is between 6 and 16 V, the output voltage V _D2 of the DC-DC converter 19 increases significantly. The power transistor 11 must have a large capacity, and in the worst case, the elements of the power transistor 11 and rectifying high-voltage diodes 13 to 16 will be destroyed, and the discharge of the spark plugs 6 to 9 will In order to sustain the current, the output voltage V _D2 of the DC-DC converter 19 is approximately -2 KV, so when V _B =16 V, the current consumption increases and energy loss increases.

Conversely, if the oscillation frequency and duty of the oscillation circuit 10 are set so that the output voltage V _D2 of the DC-DC converter 19 can be generated at about -2 KV when V _B = 16 V, then when V _B = 6 V, the primary current of the transformer 12 I _D1
This has the disadvantage that the output voltage V _D2 required to sustain the discharge current of the spark plugs 6 to 9 cannot be obtained.

In addition, the power switching element of the DC-DC converter 19 (in Fig. 1, the power transistor 1
Depending on the switching speed of 1), the oscillation circuit 1
If the oscillation frequency and duty of 0 are not fixed at appropriate values, when the transformer 12 is downsized to make the DC-DC converter 19 smaller and lighter, the iron core of the transformer 12 will become saturated and the transformer 1
An overcurrent flows through the primary coil of 2, and the power switching element (power transistor 1 in Figure 1)
1) has the disadvantage that there is a risk of breakage and that it is difficult to make it smaller and lighter.

[Purpose of the invention]

An object of the present invention is to provide an ignition device for an internal combustion engine that can prevent overcurrent due to saturation of the iron core of a DC-DC converter transformer, prevent fluctuations in output voltage, and stabilize output characteristics.

[Summary of the invention]

The present invention provides DC-
The idea is to prevent damage to the power switching element and reduce its capacity by changing the oscillation frequency or duty of the DC converter. That is, in order to prevent overcurrent due to fluctuations in the output voltage V _D2 of the DC-DC converter 19 and saturation of the iron core of the transformer 12, the oscillation frequency and duty of the oscillation circuit 10 must be adjusted to match the battery voltage as shown in FIG. It can be changed according to fluctuations. Normally, the moment key switch 2 turns on starter ST, the battery voltage drops to several volts, and then key switch 2 turns on.
returns to IG and enters the idle state, the battery voltage V _{B returns to 10 V. Therefore, in Figure 2, the battery voltage V B} returns to 10 V from engine start to idle (V _B is 6 to 10 V).
Until now, the oscillation frequency was kept almost constant, the duty was as high as 70%, and the output voltage V _D2 was sufficient to sustain the discharge current of spark plugs 6 to 9, which improved combustion efficiency, fuel efficiency, and output. I'm trying to measure it.

Furthermore, when the battery voltage is 10 V or more, the primary coil current I _D1 of the transformer 12 increases as the battery voltage V _B increases, so the oscillation frequency and duty are increased and decreased as the battery voltage V _B increases. , to stabilize the output voltage V _D2 . In addition, by increasing the oscillation frequency and decreasing the duty as the battery voltage V _B increases, the output voltage V _D2 that requires the energization time of the primary coil current I _D1 of the transformer 12 can be obtained. This can be set to the minimum necessary time just before the iron core saturates, which prevents overcurrent due to iron core saturation and allows the transformer to be made smaller and lighter.

As described above, if the characteristics of the oscillation circuit 10 are made as shown in Figure 2, it is possible to prevent fluctuations in the output voltage V _D2 of the DC-DC converter 19 and overcurrent due to saturation of the iron core of the transformer 12, and to prevent the power switch from changing. It is possible to provide a small, inexpensive DC-DC converter that prevents damage to the switching element (the power transistor 11 in FIG. 1) and reduces the capacity, thereby reducing energy loss.

[Embodiments of the invention]

Examples of the present invention will be described below.

FIG. 3 shows a detailed circuit of an oscillation circuit showing an embodiment of the present invention.

In the figure, battery voltage V _B is divided by resistors 21 and 22 via resistor 20 and is supplied to the (+) input terminal of comparator 43 . A capacitor 34, a resistor 24, and a resistor 25 are connected to the (-) input terminal of the comparator 43. The other end of the capacitor 34 is grounded, the cathode of a diode 35 is connected to the other end of the resistor 24, and the anode of a diode 36 is connected to the other end of the resistor 25. The anode of the diode 35 is connected to the output terminal of the comparator 43, and the cathode of the diode 36 is connected to the output terminal of the comparator 43.
In addition, a resistor 2 is connected to the output terminal of the comparator 43.
6, 27, 23, and 33 are connected to each other. The battery voltage V _B is applied to the other end of this resistor 26 via a resistor 20, and the base of a transistor 39 is connected to the other end of the resistor 27. In addition, a comparator 4 is connected to the other end of the resistor 23.
The (+) input terminal of No. 3 is connected to a resistor 22, and the other end of this resistor 22 is grounded. Further, the other end of the resistor 33 is connected to the base of the transistor 42. Further, a capacitor 44 and a cathode of a Zener diode 37 are connected to the resistor 20, and the other ends of the capacitor 44 and the Zener diode 37 are each grounded.

Further, a battery voltage V _B is supplied to the collector of the transistor 39 via a resistor 28.
Further, the base of the transistor 40 is connected. The emitters of these transistors 39 and 40 are grounded. The collector of this transistor 40 is connected to the anode of the Zener diode 38 and the base of a transistor 41. The cathode of this Zener diode 38 is connected to the power supply V _B via a resistor 29. Further, the battery power supply V _B is connected to the collector of the transistor 41 via the resistor 30, and the emitter of the transistor 41 is connected to the battery power supply V B via the resistor 30.
A (-) input terminal of a comparator 43 is connected via a resistor 31.

Further, the resistor 32 and the base of the transistor 46 are connected to the elector of the transistor 43, and the emitter is grounded. A battery power supply V _B is connected to the other end of this resistor 32 . Further, the collector of the transistor 46 is connected to the battery power supply V _B and the output terminal D via a resistor 45, and the emitter is grounded.

In this configuration, the voltage level of the (+) input terminal of the comparator 43 is set to HIGH.
V _refH , LOW is V _refL , Zener diode 37
Let V _Z be the cathode voltage of In addition, resistance 20,
The Zener diode 37 and the capacitor 44 are used to stabilize the power line of the comparator 43. The Zener diode 37 is, for example, a 6V constant voltage diode. Resistance 21, 22, 23, 2
If each resistance value of 6 is R ₂₁ , R ₂₂ , R ₂₃ , 0R ₂₆ ,
(+) when comparator 43 turns ON and OFF
The voltage at the input terminal is set when the comparator 43 is ON,
When turned OFF, it takes the values of LOW level (V _refL ) and HIGH level (V _refH ) as shown in the following formula.

When comparator 43 is ON V _refL = R ₂₂ R ₂₃ / R ₂₁ + R ₂₂ R ₂₃・V When _Z comparator 43 is OFF V _refH = R ₂₂ / R ₂₁ (R ₂₃ + R ₂₆ ) + R ₂₃・V _Z comparator 43 The (-) input terminal voltage of the fourth
The solid lines in Figures a and d indicate the (+) input terminal voltage, and the dotted line indicates the (+) input terminal voltage.

When key switch 2 enters IG, the electronic voltage of capacitor 34 (comparator 4
Since the (-) input terminal voltage of 3) is 0V and the (+) input terminal voltage is V _refH , the comparator 4
The output voltage V ₀ of the capacitor 3 becomes HIGH, and the output voltage V 0 of the capacitor 3 becomes HIGH.
A charging current flows through 4, and the (-) of comparator 43
The input terminal voltage rises to (+) input terminal voltage V _refH
At the moment when the output voltage of the comparator 43 exceeds
V ₀ becomes LOW, the (+) input terminal voltage drops to V _refL , and the charge accumulated in the capacitor 34 is transferred to the comparator 4 via the resistor 25 and the diode 36.
3, the (-) input terminal voltage of the comparator 43 decreases, and at the moment it becomes lower than the (+) input terminal voltage V _refL , the output voltage V ₀ of the comparator 43 becomes HIGH, and ( +) Input terminal voltage rises to V _refH .

As shown above, resistors 21 to 26 and diode 3
5, 36, a capacitor 34, and a comparator 43 constitute an unstable multivibrator, and the charging and discharging currents of the capacitor 34 can be set independently by diodes 35 and 36. For example, as shown in Figure 2, V _B =
Set the voltage to 6V, the oscillation frequency to 10KHz, and the duty (=HIGH time of the output voltage of comparator 43 x 100/period (%)) to 70%. Figure 4a shows the (+) input terminal voltage (dotted line) and (-) of the comparator 43.
The input terminal voltage (solid line) is shown, and the output voltage waveform of the comparator 43 is shown in FIG. 4b. When the output voltage _V0 of the comparator 43 becomes HIGH, the base current of the transistor 42 flows through the resistor 33, the transistor 42 is turned on, and the resistor 32
Since the base current of the transistor 46 does not flow through the transistor 46, the transistor 46 is turned off, and the base current of the power transistor 11 shown in FIG. 1 flows through the resistor 45 and the D terminal, so the power transistor 11 is turned on. Excitation current shown in figure c
I _D1 flows. Then the comparator output voltage V ₀ is
When it becomes LOW, transistor 42 is turned off, transistor 46 is turned on, and transistor 11 is turned off.
Therefore, due to the energy stored in the transformer 12, a medium-high voltage of approximately 2KV is generated on the secondary side of the transformer 12, which is rectified by the diodes 13 to 16.
The terminal voltage V _D2 of the capacitor 17 is charged with a voltage of about -2KV.

Next, the output voltage V ₀ of comparator 43 is HIGH
In this section, in addition to the normal charging route for the capacitor 34 described above, a circuit that supplies charging current is connected to the resistor 3.
7 to 31, transistors 39 to 41, and a Zener diode 38, which will be explained below.

The Zener diode 38 is, for example, a constant voltage diode of approximately 9V.

When the output voltage V ₀ of the comparator 43 is HIGH, the base current of the transistor 39 flows through the resistors 26 and 27, turning the transistor 39 ON.
However, in order to draw the current flowing through the resistor 28, the transistor 40 is turned off. Here, when the battery voltage V _B is 10V or more, the Zener diode 3
8 reverse breakdown, resistor 29, Zener diode 38
through the emitter follower configuration transistor 4
The base current flows through the transistor 1, the transistor 41 turns on in the active region, and the capacitor 3
A charging current flows through the comparator 43, accelerating the rise of the inverting terminal voltage of the comparator 43. According to this circuit configuration, the charging current supplied from transistor 41 also increases as V _B rises, so the charging time of capacitor 34 is shortened as V _B rises.

Next, when the output voltage of the comparator 43 becomes LOW, contrary to the operation described above, the transistor 3
Since transistor 9 is turned off and transistor 40 is turned on,
The base current of transistor 41 is
0, transistor 41 turns off,
Charging current is no longer supplied to the capacitor 34.

Therefore, as V _B rises, capacitor 3
Although the charging time of 4 is shortened, the discharging time is fixed by the time constant determined by the capacitor 34 and resistor 25, and as shown in Figure 2, V _B is 10V.
Above this, the oscillation frequency increases and the duty decreases. In Figure 4 d, e, and f, V _B is approximately
The waveform at 13.1V is shown. d is comparator 43
The waveforms of the inverting terminal voltage (solid line) and non-inverting terminal voltage (dotted line) are shown, e is the output voltage _V0 waveform of the comparator 43, and f is the waveform of the excitation current I _D1 flowing through the primary coil of the transformer 12 in FIG. shows.

Next, when V _B is less than 10V, Zener diode 3
8 does not undergo reverse breakdown, and the charging current flowing to the capacitor 34 through the transistor 41 is supplied only by the leakage current of the Zener diode 38.
The oscillation frequency and duty of the astable multivibrator remain at 10KHz and 70%, which were set when V _B = 6V, and hardly fluctuate.

FIG. 5 shows another embodiment of the invention. In this embodiment, the oscillation frequency of the DC-DC converter is fixed, and only the ON duty is changed according to the battery voltage.

In the figure, 50, 5, 52, 53, 54, 5
5, 56, 57, 58, 59, 60, 61, 6
2, 63, 64, 65 are resistances, 66, 67, 68
is a capacitor, 69 and 70 are comparators, and 7
1 and 72 are diodes, 73 and 74 are Zener diodes, and 75 is a transistor, the D terminal is connected to the base of the power transistor 11 shown in FIG. 1, and the V _B terminal is connected to the key switch 2 shown in FIG.
is connected to the IG terminal of the

Now, let the terminal voltage of the (+) input terminal of the comparator 69 be V ₁ , and the HIGH level of this voltage V ₁ is
V _1H , the LOW level is V _1L , and the terminal voltage of the (+) input terminal of the comparator 70 is V ₂ , (-)
Let the terminal voltage of the input terminal be _V3 , and the reverse breakdown voltage of the Zener diode 74 be _VZ74 .

In such a configuration, the power supply lines of the comparators 69 and 70 are stabilized by the resistor 65 and the Zener diode 74. Now, let the resistance values of resistors 50, 51, 52, and 54 be R ₅₀ , R ₅₁ ,
If R ₅₂ and R ₅₄ , comparator 69 is ON,
When turning OFF, the (+) input terminal voltage V ₁ changes between LOW level (V _1L ) and HIGH level (V _1H ) as shown in the following formula depending on whether the comparator 69 is ON or OFF.
takes the value of

When comparator 69 is ON V _1L = R ₅₁ R ₅₄ / R ₅₀ , R ₅₁ R ₅₄・V _Z74 When comparator 69 is OFF V _1H = R ₅₁ / R ₅₀ (R ₅₂ + R ₅₄ ) + R ₅₁・V _Z74 comparator 69 (-) input terminal voltage to the 6th
It is shown in Figure A as a dotted line, and the (+) input terminal voltage V ₁ is shown as a solid line.

In Fig. 1, when the key switch 2 enters IG, the (-) input terminal voltage of the comparator 69 in Fig. 5 is 0V, and the (+) input terminal voltage _V1 is _V1H , so the output voltage of the comparator 69 is becomes HIGH, a charging current flows into the capacitor 66 via the resistors 52 and 53, the (-) input terminal voltage of the comparator 69 rises, and at the moment it exceeds the (+) input terminal voltage _V1H , the voltage at the comparator 69's (-) input terminal increases. Output voltage is LOW
, the (+) input terminal voltage decreases to V _1L , and the charge accumulated in the capacitor 66 is discharged via the resistor 53 through the route of the output terminal of the comparator 69, and the (-) input terminal voltage of the comparator 69 decreases. decreases, and at the moment it becomes lower than the (+) input terminal voltage V _L1 , the output voltage of the comparator 69 becomes HIGH, and the (+) input terminal voltage rises to V _1H . As described above, the resistors 50 to 54, the capacitor 66, and the comparator 69 constitute an unstable multivibrator. The above-mentioned unstable multivibrator can be made by properly selecting the Zener diode 74 (for example, 5V
~6V) The oscillation frequency can be fixed constant from startup to high speed range. The oscillation frequency is set to an appropriate value so as to reduce energy loss in the ignition device.

Resistors 55 to 65, capacitors 67 and 68, comparator 70, diodes 71 and 72, Zener diode 73, and transistor 75 constitute a one-shot multi-circuit. First, resistance 6
0. The configuration will be explained without the Zener diode 73. Transistor 75 is for inverting the output of the unstable multivibrator, and FIG. 6B shows the collector voltage waveform. capacitor 67, resistor 5
7 constitutes a differential circuit, and the differential waveform is rectified by a diode 71 and applied to the (+) input terminal in order to trigger the comparator 70 at the rise of the collector voltage of the transistor 75. The above trigger has a constant frequency because it is synchronized with the unstable multivibrator, and although it cannot be confirmed in the mounted state, it has the waveform shown in Figure 6c, and the trigger is applied to the (+) input terminal of the comparator 70. , the trigger voltage is HIGH than the (-) input terminal voltage V ₃
Since the output voltage of the comparator 70 is
becomes HIGH, resistors 63, 64, capacitor 6
8. A current flows through the route of the resistors 62 and 61, and a voltage expressed by the following equation is generated at the (+) input terminal V ₂ of the comparator 70.

Each resistance value of resistors 61, 62, 63, 64;
R ₆₁ , R ₆₂ , R ₆₃ , R ₆₄ Capacity of capacitor 68; C ₆₈ R = R ₆₁ + R ₆₂ + R ₆₃ + R ₆₄ (+) input terminal voltage V ₂ shown in the above formula is (-)
Comparator 7 only when input terminal voltage V ₃ or higher
Since the output of 0 is HIGH, the DC
-DC converter power transistor 11
Turn on.

FIG. 6D shows the (+) input terminal voltage V ₂ and (-) input terminal voltage V ₃ of the comparator 70, and FIG. 6E shows the D terminal voltage waveform. The diode 72 is for negative surge protection of the comparator 70.

Next, the functions of the resistor 60 and Zener diode 72 will be explained. For example, the Zener diode 73 is set so that it can be turned on when the battery voltage is 10V.If the battery voltage is less than 10V, the Zener diode 73 will not turn on, so the reverse breakdown current will be low.
I _Z is 0, and the (-) input terminal voltage V ₃ of the comparator 70 is determined only by the division ratio of the resistors 58 and 59. Since the period of the voltage waveform at the D terminal is fixed by an unstable multivibrator, when the battery voltage is less than 10V, the ON duty (=ON time x 100/period (%)) of the power transistor 11 in Fig. 1 is changed to, for example, Resistor 58, so that it is 70%.
Set 59. The voltage waveforms when the battery voltage is less than 10V are shown in FIGS. 6D and 6E.

When the battery voltage becomes 10V or more, the Zener diode 73 is turned on, and the current I _Z flowing through the Zener diode 73 is changed according to the battery voltage.

I _Z and V ₃ are expressed by the following equations.

I _Z = V _B −R ₅₉ /R ₅₈ +R ₅₉・V _Z74 −V _Z73 /R ₆₀ V ₃ =R ₅₉ (V _Z74 /R ₅₈ +R ₅₉ +I _Z ) V _B : Battery voltage Resistors 58, 59, 60 Each resistance value; R ₅₈ , R ₅₉ ,
R ₆₀ Reverse breakdown voltage of Zener diode 73; V _Z73 (+) input terminal voltage of comparator 70 V ₃ is
I _Z・R Increases by ₅₉ . FIG. 6F shows the voltage waveforms of V ₂ and V ₃ of the comparator 70, and FIG. 6G shows the D terminal voltage waveform. As the battery voltage rises, _V3 rises and the HIGH level part of the D terminal waveform is shortened, causing the first
The ON duty of the power transistor 11 shown in the figure decreases.

Another embodiment of the invention is shown in FIG.
In this embodiment, the ON duty of the DC-DC converter is fixed, and only the oscillation frequency is changed according to changes in battery voltage.

In the figure, 80, 81, 82, 83, 84,
85, 86, 87, 89, 90, 91, 92, 9
3,94,65,96,97,98,99,10
0, 101, 102 are resistances, 103, 104, 1
05 is a zener diode, 106, 107, 10
8, 109 are diodes, 110, 111, 11
2,113,114,115,116,117 are
NPN transistors, 118, 119 are PNP transistors, 120, 121, 122 are capacitors, 123, 124 are comparators, the D terminal is connected to the base of the power transistor 11 shown in Figure 1, and the V _B terminal is connected to the base of the power transistor 11 shown in Figure 1. key switch 2
Connected to the IG terminal. This resistor 80 and Zener diode 104 are PNP transistor 118
The resistor 84 and the Zener diode 105 are used to stabilize the power lines of the comparators 123 and 124. In addition, resistors 85, 86, 87, 88, 89,
An unstable multivibrator is configured by the capacitor 120 and the comparator 123, and when the output of the comparator 123 is at HIGH level, the capacitor 120 is A charging time reduction circuit is configured.

In such a configuration, the Zener diode 1
03 is set to turn on when the battery voltage V _B is, for example, 10V. Now, when V _B <10 [V], the Zener diode 103 does not turn on, so the transistor 110 turns off, and the charging time reduction circuit of the capacitor 120 does not operate, and the (+) input terminal voltage waveform of the comparator 123 at this time is shown by a solid line in FIG. 8A, and the (-) input terminal voltage waveform is shown by a dotted line. Also, resistance 9
0,91, and the transistor 111 constitute an inverter circuit, the unstable multivibrator output voltage is inverted, and the collector voltage of the transistor 111 has the waveform shown in FIG. 8B. capacitor 1
21, a differential circuit is configured by the resistor 92, and at the rise of the collector voltage waveform of the transistor 111,
In order to obtain a trigger to be applied to the base of transistor 99 of a bistable circuit composed of resistors 98, 99, 100, diode 109, and transistors 115, 116, the signal is rectified by diode 108 into a differentiating circuit output waveform. Since the charging time reduction circuit for the capacitor 120 is not operating, the rectified trigger waveform becomes a voltage waveform with a frequency shown in FIG. 8C.

Next, a case where the battery voltage V _B is 210V will be explained.

When the output voltage of the comparator 123 is at HIGH level, the capacitor 120 includes a resistor 89,
In addition to the charging current flowing through resistor 87, there is a charging current flowing through resistor 83. Battery voltage V _B
When the comparator output is at HIGH level at 210V, transistor 111 is turned on and transistor 12 is turned on.
6 is OFF, so resistor 8 is connected from the battery voltage V _B.
1. The reverse breakdown current of the Zener diode 103 flowing through the Zener diode 103 is not drawn into the transistor 126 but flows into the base of the transistor 110, so the transistor 110 is turned on.
do. The transistor 110 has an emitter follower configuration and operates in the active region, with the resistor 82, the collector of the transistor 110, the emitter, and the resistor 8
3, a charging current that changes depending on the battery voltage _VB is supplied to the capacitor 120. Therefore, the rise of the (-) input terminal voltage of the comparator 123 is accelerated, and the charging time of the capacitor 120 is shortened.

Next, when the output voltage of the comparator 123 is at the LOW level, the transistor 111 is turned off.
126 is turned ON, the reverse breakdown current of the Zener diode flowing through the resistor 81 and the Zener diode 103 from the battery voltage _VB is the transistor 12.
6 and does not flow to the base of transistor 110, transistor 110 is turned off.
The charging current of the capacitor 120 does not flow through the route of the resistor 82, transistor 110, and resistor 83.
When the output voltage of the comparator 123 is at LOW level, the charge accumulated in the capacitor 120 is discharged through the route of the resistor 87 and the output terminal of the comparator 123, and the charging time reduction circuit of the capacitor 120 does not operate. It has the same discharge time as the falling section shown by the dotted line in Figure 8A. From the above, when V _B is 10V, only the charging time of the capacitor 120 is shortened by the charging time shortening circuit. The (+) input terminal voltage waveform of the comparator 123 is
It is shown in Figure F by a solid line, and the (-) input terminal voltage waveform is shown by a dotted line. Transistor 11 for V _B 10V
The collector voltage waveform of 1 is shown in FIG. 8G, and the trigger waveform rectified by the diode 108 is shown in FIG. 8H.

For V _B < 10V the trigger frequency is constant and V _B
At 10V, the trigger frequency increases as the battery voltage _VB increases.

Next, the duty of the D terminal output will be explained.
When a trigger waveform rectified by diode 108 (e.g., FIG. 8C) is applied to the base of transistor 116, transistor 116 is turned ON.
However, since the current flowing through the resistor 100 is drawn into the transistor 116, no base current flows through the resistors 97 and 99, and the transistors 113 and 1
15 is turned off.

When the transistor 113 turns off, the resistor 93
A current mirror constant current circuit consisting of a diode 106 and a transistor 114 operates, discharging the charge in the capacitor 122 with a constant current I ₂ , and the terminal voltage of the capacitor 122 rises at a constant slope. Go up. I ₂ is expressed by the following formula.

I ₂ = V _Z −V _F2 /R ₉₃ V _Z : Zener voltage of Zener diode 105 V _F2 : Forward voltage of diode 106 R ₉₃ : Resistance value of resistor 93 The terminal voltage of capacitor 122 is the same as that of resistors 95 and 96.
When the potential becomes the same as the divided potential of the comparator 124
The output voltage becomes LOW level, the current flowing through the resistor 98 is drawn into the output terminal of the comparator 124, and the base current does not flow into the transistor 116 through the diode 109, so the transistor 116 is turned off. transistor 1
When 16 turns off, transistors 115 and 11
3 turns on. When transistor 113 turns on, the base voltage of transistor 114 becomes 0V,
Transistor 114 turns OFF and capacitor 12
Stop the discharge of step 2.

On the other hand, resistor 94, diode 107, transistor 112, PNP transistors 118 and 119
Due to the current mirror circuit consisting _of
The terminal voltage of is charged with a constant slope determined by the constant current _I1 . Constant current I ₁ is expressed by the following formula.

I ₁ = V _Z −V _F1 /R ₉₄ V _Z : Zener voltage of Zener diode 105 V _F1 : Forward voltage of diode 107 R ₉₄ : Resistance value of resistor 94 In other words, terminal voltage V _C of capacitor 122 is calculated by the following formula. shown. Let the terminal voltage of the capacitor 122 be V _C1 when charging, and V _C2 when discharging.

V _C1 = I ₁ /Ct + V _ref C: Capacity of capacitor 122 t: Time V _ref : Voltage at the dividing point between resistors 95 and 96 In the above equation, the terminal voltage of capacitor 122 increases,
A trigger signal applied to the base of the transistor 116 starts discharging with a constant current, and the terminal voltage V _C2 during discharging is expressed by the following equation.

V _C2 = I ₁ + I ₂ /Ct + V _C11 V _C11 : Terminal voltage of the capacitor 122 immediately before discharge starts V _C1 Therefore, the capacitor 122 is discharged, and the terminal voltage V _C2 becomes equal to the (-) input terminal voltage of the comparator 124. When they become equal, discharging stops and switches to charging, and the transistor 116 is charged until a trigger signal is input, and when the trigger signal is input, it switches to discharging, and this operation is repeated, so that the terminal voltage of the capacitor 122 becomes It becomes a triangular wave as shown in Figure 8D. The resistors 93 and 94 are set to satisfy the following equation, and are set so that the triangular wave does not saturate when V _B <10V.

R ₉₃ /R ₉₄ =V _Z -V _F2 /V _Z V _F1 (1-α/100) V _Z : Zener voltage of Zener diode 105 V _F1 : Forward voltage of diode 107 V _F2 : Forward voltage of diode 108 α: ON duty of the power transistor 11 in FIG. 1 During the rise time of the triangular wave shown in FIG. does not flow, the transistor 117 is turned off, and the transistor 115 is turned off during the falling time of the triangular wave.Since the input of the comparator 124 is at HIGH level, the base current flows to the transistor 117 via the resistor 102, and the transistor 117 turns on. Therefore, the collector voltage waveform of the transistor 117 becomes as shown in FIG.
Power transistor 1 of the DC-DC converter shown in the figure
1 base.

Here, since the charging/discharging current of the triangular wave is constant regardless of fluctuations in the battery voltage, the period (frequency) of the trigger signal applied to the base of the transistor 116 has no relation to the rise time of the triangular wave As a result, the ON duty of the power transistor shown in FIG. 1 is always constant.

Therefore, with the circuit configuration shown in FIG. 7, it is possible to keep the ON duty constant and change the frequency according to fluctuations in battery voltage.

The battery voltage V _B 10V is shown at I and J in Figure 8.
The terminal voltage waveform of capacitor 122 and the collector voltage waveform of transistor 117 are shown in FIG.

〔Effect of the invention〕

As described in detail above, according to the oscillation circuit included in the DC-DC converter of the present invention, the oscillation frequency and duty of the DC-DC converter are changed according to fluctuations in battery voltage. The DC-
This has the effect of preventing destruction of the power switching element included in the DC converter and realizing a reduction in capacity, and also has the effect of providing an ignition device that is small, inexpensive, and has little energy loss.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of an ignition system using a conventional DC-DC converter, Fig. 2 is a characteristic diagram of an oscillation circuit, Fig. 3 is an oscillation circuit diagram showing an embodiment of the present invention, and Fig. 4 is a diagram of an ignition system using a conventional DC-DC converter. 5 is an oscillation circuit diagram showing an embodiment of the present invention, FIG. 6 is a waveform diagram of each part of FIG. 5, and FIG. 7 is an oscillation circuit diagram showing an embodiment of the present invention.
FIG. 8 is a waveform diagram of each part of FIG. 7. 1...Battery, 2...Key switch, IG...
...IG switch, ST...starter switch, 3...
...IC igniter, 3a...Pickup coil,
4...Ignition coil, 5...Distributor, 6-9...Spark plug, 10...Oscillation circuit, 11...Power transistor, 12...Transformer, 13-16...
Rectifier high voltage diode, 17...Capacitor, 1
8a-18f...High voltage cord, 19...DC-DC
Converter, I ₁ ... Ignition coil primary current, V ₂ ...
Secondary voltage, I _D1 ... Excitation current of DC-DC converter, V _D2 ... Output voltage of DC-DC converter.

Claims (1)

[Scope of Claims] 1. A power distributor equipped with a mechanical power distribution mechanism, an ignition device that generates a high voltage pulse necessary to break down the insulation between the spark plug electrodes, and a In an ignition system for an internal combustion engine equipped with a medium-high voltage DC-DC converter for further continuing the discharge current after dielectric breakdown occurs, the frequency of the oscillation circuit provided in the DC-DC converter is set to the battery voltage. An ignition device for an internal combustion engine, characterized in that the ignition device changes accordingly. 2. A power distributor equipped with a mechanical power distribution mechanism, an ignition device that generates the high voltage pulse necessary to break down the insulation between the spark plug electrodes, and a device that causes the insulation breakdown between the spark plug electrodes by the ignition device. In an ignition system for an internal combustion engine equipped with a medium-high voltage DC-DC converter for further continuing the discharge current after discharge, the power is switched by a signal output from an oscillation circuit included in the DC-DC converter. An ignition device for an internal combustion engine, characterized in that the duty of a switching element is changed according to battery voltage. 3. A power distributor equipped with a mechanical power distribution mechanism, an ignition device that generates the high voltage pulse necessary to break down the insulation between the spark plug electrodes, and a device that causes the insulation breakdown between the spark plug electrodes by the ignition device. In an ignition system for an internal combustion engine equipped with a medium-high voltage DC-DC converter for further continuing the discharge current after discharge, the frequency of an oscillation circuit provided in the DC-DC converter and the frequency of an oscillation circuit provided in the An ignition device for an internal combustion engine, characterized in that the duty of each power switching element is changed in accordance with changes in battery voltage.