JPS5827094Y2 - Ignition circuit for internal combustion engines with overheat prevention circuit - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to overheating prevention of a power transistor in an ignition circuit for an internal combustion engine configured to use a transistor to conduct and interrupt the primary forward current flowing through the primary winding of a magneto's ignition coil. It is.

Conventionally, when cutting off the forward current on the primary side of the ignition coil of a transistorized ignition circuit for an internal combustion engine, a magneto is used to prevent the power transistor of the ignition circuit from overheating and to maintain proper ignition timing up to high speed rotation. When a reverse current limiting circuit is added to limit the reverse current that acts to delay the establishment of the forward current of the primary alternating current flowing through the primary winding of the ignition coil, this increases the terminal voltage of the primary winding and interrupts the primary forward current. As a result, the secondary side of the ignition coil cannot generate enough ignition energy to ignite the internal combustion engine.

The purpose of this invention was to solve the above-mentioned problems by passing a primary alternating current forward current through a transistorized internal/combustion engine ignition circuit in a short-circuited state, and cutting off its maximum value at the starting rotational speed of the internal combustion engine. The ignition circuit for an internal combustion engine ensures generation of sufficient spark energy to ignite the internal combustion engine in the secondary winding of the ignition coil, and limits only the reverse current of the primary alternating current without reducing the forward current. The object of the present invention is to provide the power transistor in a circuit to prevent overheating of the power transistor in the circuit and to maintain proper ignition timing.

An embodiment of the present invention will be described below with reference to the accompanying drawings.

, T is a magneto ignition coil, which is made up of an iron core F wound with a primary winding T1 and a secondary winding T2 having a higher turns ratio.

P is a spark plug, and its insulated electrode is connected to the winding end terminal of the secondary winding T2.

Ground electrode of spark plug P, negative winding T1 and secondary winding T
The winding start terminal No. 2 is grounded.

Qa is a composite connection circuit in which the collector and base of an NPN power transistor Q2 are connected to the emitter and collector of a PNP transistor Q, respectively.

Re is diode D.

This is a rectifier Re in which a constant voltage diode D2 and a constant voltage diode D2 are connected in parallel in the same forward direction.

The composite connection circuit Qa is connected between both terminals of the secondary winding T1.
The emitter E and collector C are inserted and connected through the rectifier Re with the collector C side aligned in the forward direction, so that the emitter E is on the ground side.

The base B of the composite connection circuit Qa is connected through a series circuit of a temperature compensation resistor R1 and a resistor R8, which is configured by connecting a resistor r2 in series with a resistor r2 connected in series with a thermistor r1, and further connecting a resistor r3 in series. It is connected to the ungrounded terminal of the secondary winding T1.

The anode A1 cathode K and gate G of a thyrisk equivalent circuit Th, which is formed by connecting the collector of a PNP type transistor Q3 to the base of an NPN type transistor Q4, and further connecting the base of the transistor Q3 to the collector of the transistor Q4, They are respectively connected to the ground side terminal of the secondary winding T1, the connection point between the temperature compensation resistor R1 and the resistor R8, and the base B of the composite connection circuit Qa.

The circuit configuration of the present invention is as described above, and as the internal combustion engine rotates, an alternating current voltage is generated between both terminals of the primary winding T1 of the magneto's ignition coil T.

- When a terminal voltage that makes the ground side terminal of the next winding T1 a positive voltage starts to be generated, the base current of the composite connection circuit Qa passes through the base B of the composite connection circuit Qa and connects the temperature compensation resistor Rt and the resistor R8 in series. The collector current that flows through the circuit as a bias resistor and is then greatly amplified by the transistor Q1 and the power transistor Q2, that is, the primary forward current of the primary winding T1, flows between the emitter E and the collector C of the composite connection circuit Qa, and the primary forward current of the primary winding T1 flows through the rectifier Re. flows through.

When the base current of the composite connection circuit Qa flowing through the temperature compensation resistor R1 increases, the voltage drop increases across the transistor Q4.
Transistor Q4 becomes conductive when the base-emitter voltage VBB4 of
3 continues to conduct, shorting between the base B and emitter E of the composite connection circuit Qa.

Thus, the thyrist equivalent circuit Th acts as a control circuit for the primary forward current of the primary winding T1, and sharply cuts off the primary current of the primary winding T1 conducting between the emitter and collector C of the composite connection circuit Qa.

Due to the electromagnetic induction effect caused by this interruption, a high voltage is induced in the secondary winding T2 of the ignition coil T with a high number of turns, and a spark discharge occurs in the spark plug P.

The starting rotational speed n8 of the internal combustion engine is generally low, and in order to reliably start the engine at this low rotational speed l, it is necessary to generate a high-pitched sound of at least a few kilovolts in the secondary winding T2.

For this purpose, it is necessary to cut off the forward current when it reaches its maximum value, that is, the voltage drop Rt·1B across the temperature compensation resistor R1 due to the base current IB of the composite connection circuit Qa corresponding to this maximum current value. The value of the temperature compensation resistor Rt is set in advance so that the thyrisk equivalent circuit Th becomes conductive.

The terminal voltage (1) of the primary winding T1 corresponding to the maximum value of this forward current is VBEI, which is the base-emitter voltage and collector-emitter voltage of the transistor Q1 and power transistor Q2 at this time.

VBE2 and VOEI, VOB2, rectifier Re
If the forward voltage of is vpo, it is given by the following balanced equation.

V1=(-VBEl)+R1-IB+RoI B=(-
VOEI)-)-VBE2-)-VFO=VOE2+V
F0 In this equation, Rt·IB−VBE4, and the forward voltage VFO of the rectifier Re is generally smaller than the forward voltage of the constant voltage diode D2.

The -order forward current is determined by the forward voltage of diode D.

flows through. Therefore, if each transistor, diode, and voltage regulator diode in this circuit are made of silicon, it can be regarded as -vBE1+vBE2÷VBE4÷VFO,
Since these voltages have respective threshold values and are the largest values among the terms in the previous equation, as a result, the terminal voltage v1 of the primary winding T1 is the largest value in the previous equation (-VB E
1)+VB E 4+R(, is determined by IB and is not affected by the presence or absence of the rectifier Re.

In other words, the rectifier Re is connected to the collector C of the composite connection circuit Qa.
The maximum value of the primary forward current at the starting rotational speed n8 does not change whether or not it is inserted and connected between the ungrounded terminal of the primary winding T1 and the ungrounded terminal of the primary winding T1.

Following the interruption of the primary forward current of the primary winding T1, the -order reverse voltage begins to be applied between the emitter E and collector C of the composite connection circuit Qa and to the series circuit of the rectifier Re. Zener voltage V2 of voltage regulator diode D of Re and collector-open emitter-base voltage V of power transistor Q2
No primary reverse current flows through this series circuit until the rotational speed n□ of the internal combustion engine reaches the sum of EB20.

The collector-open emitter-base voltage VEB20 of the power transistor Q2 has a substantially constant value of about 10 volts, and therefore the rotational speed n at which the primary reverse current begins to flow.

depends on the magnitude of the Zener voltage 2 of the constant voltage diode Dz, and the rotational speed n of the internal combustion engine.

The primary reverse current increases from 1 to 5 nm to its maximum rotational speed of nm.

On the other hand, the power transistor Q2 generates an emitter loss equal to the product of this primary reverse current value and the collector-open emitter-base voltage VEBO2, and the larger the emitter loss, the more the power transistor Q2 overheats, and if it is used for a long time in this overheated state, the current amplification factor increases. Decrease in hFE2, emitter cut-off current IEB
This results in changes in performance over time, such as an increase in 02.

Therefore, even at the maximum rotational speed nm, the constant voltage diode D2 is kept at a temperature that does not cause the power transistor Q2 to overheat.
The primary reverse current must be limited by raising the Zener voltage v2 of

If the primary reverse current is allowed to flow through the primary winding T1 without being restricted, the establishment of the primary forward current that subsequently flows and is cut off will be delayed as the rotational speed of the internal combustion engine increases, and therefore the ignition of the internal combustion engine will be delayed. As mentioned above, in order to prevent the power transistor Q2 from overheating, the primary reverse current is limited by the constant voltage diode D2, thereby preventing a delay in establishing the primary forward current, thereby reducing the timing of the internal combustion engine. Ignition timing is almost constant at medium and high speeds, starting rotation speed n5
In this range, the timing is slightly delayed, and the constant voltage diode D2 can have the effect of maintaining proper ignition timing over the entire rotational speed range of the internal combustion engine, as well as the overheating prevention effect of the power transistor Q2.

Diode υ of rectifier Re.

The average rectifying current capacity of the rectifier Re can be as small as 3 Anherr class, and the power dissipation of the constant voltage diode D2 (Zener voltage 2 x Zener current 2) can be as small as 1 Watt class. It is also the smallest transistor Q3 among the transistors in this ignition circuit.

Compared to Q4, the size is still several times smaller than that of Q4, and even if this is inserted and connected to the main ignition circuit, the overall structural size of the circuit will not be particularly increased.

Transistor Q3 +Q4 of thyristor equivalent circuit Th
During this time, a current positive feedback action takes place.

That is, when the base current of the transistor Q4 flows due to the voltage drop Rt·IB of the temperature compensation resistor Rt, the collector current thereof flows.

Since this collector current is the base current of transistor Q3, the collector current of transistor Q3 flows and acts to promote the initial base current of transistor Q4.

Therefore, transistor Q3. A positive current feedback action immediately spreads between Q and Q, and the thyrisk equivalent circuit Th instantly becomes conductive, shorting the base B and emitter E of the composite connection circuit Qa.

The primary forward current flowing between the emitter E and the collector C of the composite connection circuit Qa is interrupted in an extremely short time due to the current positive feedback action of the thyrisk equivalent circuit Th, and the secondary winding T2 of the ignition coil T is connected to the internal combustion engine can generate enough spark energy to ignite.

As is clear from the above explanation, it is simply a diode D.

By inserting and connecting a rectifier Re, which has an extremely simple and compact configuration of a parallel connection of a voltage regulator diode D2 and a voltage regulator diode D2, into the collector current path of the composite connection circuit Qa,
Without reducing the primary forward current to be cut off and with its excellent cutoff function, the secondary voltage required for low starting rotational speed is sufficiently secured, and the power transistor Q2
It protects the internal combustion engine from changes over time due to overheating, maintains the ignition timing of the internal combustion engine properly, and serves as an ignition circuit for the internal combustion engine to start the engine.
Good driving conditions can be provided.

[Brief explanation of the drawing]

The drawing is an electrical circuit diagram showing an embodiment of the present invention. T...Ignition coil, F...Iron core, T1
・・・・・・−Secondary winding, T2・・・Secondary winding,
P...Spark plug, Q, ,Qa,Q,
...Transistor, Q2...Power transistor, Qa...Composite connection circuit, Th,...
...Thyristor equivalent circuit, C...Collector, E...Emitter, B...Base, A
...Anode, G...Gate, K...
...Cathode, D. ...Diode, D2 ... Constant voltage diode, Re ... Rectifier, R□ + rl,
r2, r3°°°°゛°resistance, rl...
Thermistor, Rt...Temperature compensation resistance.

Claims (1)

[Claims for Utility Model Registration] One terminal of the primary winding T1 of the magneto's ignition coil T is grounded, and this and the emitter E of a composite connection circuit Qa consisting of a PNP type transistor Q1 and an NPN type power transistor Q2. A direct circuit of a temperature change compensation resistor Rt and a resistor R8 is connected between the base B of the composite connection circuit Qa and the ungrounded terminal of the secondary winding T1, and a PNP type transistor Q2 and an NPN The anode A1 gate G and cathode K of the silice equivalent circuit Th consisting of a transistor Q4 of the form
A diode D is connected between the collector C of the composite connection circuit Qa and the ungrounded terminal of the negative secondary winding T1. A rectifier Re consisting of a parallel circuit of a constant voltage diode Dz
An ignition circuit for an internal combustion engine with an overheat prevention circuit, characterized in that an overheat prevention circuit is inserted and connected.