JPH0125904Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a capacitor discharge type ignition device, and in particular provides a stable ignition device that protects the converter circuit in the event of a short circuit on the secondary side due to failure of commutation of a thyristor, and prevents failure of commutation. This is the purpose.

This will be explained below using the drawings.

Figure 1 is a circuit diagram showing one embodiment of the device of the present invention, where BAT is a battery, SW is a power switch, and A
is a transistor converter, B is an ignition circuit, and converter A will be explained below.

In the figure, T is a step-up transformer, n1 and n2 are the base winding and collector winding provided on the primary side,
n3 is an output winding provided on the secondary side, Q1 and Q2 are oscillation transistors configured in a so-called Darlington connection, and the base electrodes of the transistors Q1 and Q2 are connected to the base winding via a diode D2 or D3, respectively. n1 is connected to one end of each, and the emitter electrodes are commonly connected to the (-) of the battery BAT.
connected to the side. Further, each collector electrode is connected to one end of the collector winding n2. Further, the positive electrode of the battery BAT is connected to the other end (intermediate terminal) of the collector winding n2.

Q3 is the positive terminal of the battery and the base winding n1
An auxiliary transistor with an emitter electrode and a collector electrode connected in series between the other ends (intermediate terminals);
Q4 and Q5 are control transistors for controlling the conduction of the auxiliary transistor Q3, and the transistors Q3 to Q5 form a control switch for the oscillation transistors Q1 and Q2. REC is a bridge rectifier that rectifies the secondary side (n3) voltage of the step-up transformer T. Next, in the ignition circuit B, C2 is a capacitor charged by the rectified output, S,
Tg and Ip are a thyristor with a control pole (SCR), an ignition transformer, and a spark plug that constitute a means (circuit) for selectively discharging the charge in the capacitor C to operate a spark plug; G is a thyristor S; Gate circuits D6 and D7 are diodes connected in series with the thyristor, and the control transistor Q5 is controlled by the voltage across the diodes. The circuit of the present invention is configured as described above.

In the above configuration, when the power switch SW is turned on, the control transistor Q5 is turned off because the base current is not supplied, and the transistor Q
4 is turned on because the base current flows through R2, and transistor Q3 is turned on because Q4 is turned on.
It becomes ON. As a result, a base current flows through the following paths: transistor Q3 → capacitor C1 → resistor R4 base winding n1 → diode D2 → diode D3 oscillation transistor Q1 or Q2. Here, of the oscillation transistors Q1 and Q2, the one with the larger current amplification factor (hFE) turns on first, and the collector current flows. Therefore, since the base winding n1 is connected in the direction in which the base current of the oscillation transistor Q1 or Q2 that was turned ON first increases, the one that was turned ON works in the ON direction more, and the voltage of the base winding of the other transistor increases. Since the opposite occurs, it is turned OFF.
For example, if Q1 is ON first, the base winding n1
The current flows through the following path: diode D3 → base emitter of transistor Q1 → ground (one side of power supply) → diode D1 → transistor Q3 → capacitor C1 → resistor R4 = base winding intermediate terminal.

On the other hand, when Q2 is ON, the current flows through the path of diode D2 → transistor Q2 → diode D1 → transistor Q3 → capacitor C1 → resistor R4 at the other end of the base winding. When one of the transistors Q1 or Q2 is turned on, its collector current increases, and after a predetermined time, the iron core becomes saturated, and the base current (Ib) becomes insufficient, causing the transistor Q1 or Q2 to move from the saturation region to the cutoff region. hand
Turn off.

When Q1 or Q2 turns OFF, a reverse voltage appears due to the inductance and stray capacitance of the step-up transformer T, and the other transistor Q2 or Q
Turn on 1. By repeating this operation, so-called push-pull type self-oscillation is performed, and a stepped-up AC output is generated on the secondary side n3 of the step-up transformer T.

This AC output charges capacitor C2 via rectifier REC. When the thyristor S becomes conductive due to the signal from the gate circuit G, the capacitor C2
The charge of thyristor S → diodes D6, D7 →
Discharge occurs in the path of ignition transformer Tg → capacitor C2 other terminal, and due to resonance of LC, capacitor other terminal → ignition transformer Tg → rectifier
REC→Capacitor C2 resonates on the bounce path.

At this time, the thyristor S is
OFF (commutation), the current from the rectifier REC charges the capacitor C2, and the capacitor C2 is charged until it is discharged again. When the thyristor S causes a commutation failure, the thyristor S
Since the ON state continues, the secondary side of the transformer T shorts, causing an excessive current to flow through the converter transistors Q1 and Q2 and destroying them. However, according to the present invention, if commutation fails, the thyristor S current is detected and the current The converter circuit is stopped while the current is flowing, preventing the thyristor from being turned on. In other words, thyristor S fails commutation and rectifier REC
When the DC current continues to flow, the diodes D6 and D
7. Voltage is generated across both ends. This voltage supplies the base current of transistor Q5, and transistor Q5, which becomes OM, turns on, resulting in transistor Q
4, Q3 becomes OFF, and the base circuit of transistors Q1 and Q2 of the converter circuit cannot be formed.
The converter oscillation stops. This results in a rectifier
The DC current from REC stops flowing, becomes less than the holding current (IH) of thyristor S, and the thyristor turns OFF.

When turned off, no voltage is generated across diodes D6 and D7, so transistor Q5 is turned off.
Transistors Q4 and Q3 turn on, the converter starts oscillating, and the voltage boosted by transformer T is rectified by rectifier REC, and capacitor C2 is charged. In addition, the present invention enables the thyristor S to be turned on by a signal from a normal gate circuit rather than a commutation failure state.
Also when the converter stops oscillating, the thyristor
This prevents short current when the secondary side of the transformer is shorted when the transformer is turned on, and prevents wasted power from being used, which is effective in saving energy and keeping the heat generation of the ignition unit low.

As is clear from the above explanation, the present invention has the effect of preventing commutation failure of the thyristor and protecting the converter transistor.

Since it prevents the spark from continuing to burn due to failure of commutation, it is possible to prevent the spark from misfiring. (Even if it doesn't stay on for a long time, if the thyristor stays on momentarily, the capacitor C2 will not be charged during that time, no discharge energy will be applied to the ignition transformer, no spark will be produced at the plug, and the engine will stop during that time, so driving (The converter stops when the thyristor is turned on by the gate circuit signal, so no wasted energy is used during secondary shot, which is effective in saving energy and preventing heat generation in the unit.) The above effect is significant.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of one embodiment of the device of the present invention.
In the figure, Q1Q2 are oscillation transistors, Q3
Q4Q5 is a control transistor, T is a step-up transformer, n1n2n3 is its base winding, collector winding and secondary side (output) winding, REC is a rectifier, C
1C2 is a capacitor, S is a thyristor (SCR),
Tg is the ignition transformer, Ip is the spark plug,
R1-4 are resistors, D1-5 are diodes, D6,
7 is a current detection diode, G is a gate circuit that supplies pulses synchronized with the engine to thyristor S, BAT is a battery, A is a transistor converter, and B is an ignition circuit.

Claims (1)

[Scope of utility model registration request] In a capacitor charging/discharging type ignition device in which the charge of a capacitor charged by the output of a transistor converter is discharged to an ignition coil via a thyristor, a diode is provided in series with the thyristor, and the voltage across the diode is used to control the transistor. A capacitor charge/discharge type ignition device, characterized in that it controls a switch element for controlling oscillation of a converter.