JPS6394080A - Low voltage distribution type igniter for internal combustion engine - Google Patents

Abstract

PURPOSE:To block production of secondary current in reverse direction through an ignition coil, by inserting a high voltage diode in a closed circuit at the secondary of the ignition coil and specifying the breakdown voltage in the reverse direction. CONSTITUTION:When a high voltage diode 15 is inserted into the high voltage line section 12 of a closed circuit at the secondary of an ignition coil, normal secondary current is fed to an ignition plug 13 but the secondary current in reverse direction being produced through turning ON of a current blocking transistor 14 can be blocked thereby erroneous firing of the ignition plug 13 can be prevented. If the high voltage diode 15 has a breakdown voltage in reverse direction slightly higher than the opposite polarity voltage which occurs when primary current starts to flow through the ignition coil 10, e.g. 5-8kV,, the differential voltage across the high voltage diode 15 is clamped to 7kV even if the applied voltage exceeds over 40kV because of a stray capacity 16 thus causing no inconvenience such as dielectric breakdown.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a low-voltage power distribution type ignition device for an internal combustion engine, and more particularly to an improvement that effectively prevents reverse secondary current from flowing from an ignition coil to a spark plug.

<Conventional technology> Nowadays, by installing a dedicated ignition coil near each cylinder of an internal combustion engine without using a distributor, low voltage power is distributed to each ignition coil and the next winding, and high voltage is distributed to the secondary side of the ignition coil. In an attempt to shorten the wiring distance, or more aggressively, the secondary output part of each ignition coil was mechanically constructed so that it could only be connected to the spark plug, and the high voltage cord was omitted. There is something.

This is to reduce energy loss and suppress noise generation, but the concept of such a device is shown in Figure 3 for each cylinder, where low voltage wiring is routed from the ignition coil to the next side. Accordingly, each ignition coil IO is located close to each cylinder, or alternatively is attached only to the spark plug 13 for each cylinder.

Therefore, the high-voltage line section 12 on the secondary side of the ignition coil 10 is either a short wiring like a conventional lotus, or a connector that is detachably connected not only electrically but also mechanically to the ignition plug 13. It is organized as a department.

However, the ignition operation itself of such an ignition system is basically the same as that of conventional ignition systems that used a distributor to distribute high-voltage power, and the current interruption in Figure 3 is synchronized with the engine rotational position. Required transistor 1
4 turns off, as shown in Figure 4, the primary current flowing through the primary side of the ignition coil IO is abruptly cut off, and a large spike-shaped spike in the negative direction shown by the symbol ■ appears on the secondary side of the ignition coil. Voltage is generated and this is spark plug 1
3 and becomes the ignition energy in the cylinder. Specifically, this voltage can reach a maximum of about 4OKν.

<Problems to be Solved by the Invention> In the conventional ignition device described above, in addition to the normal ignition energy, the secondary side of the ignition coil also receives energy as shown by the symbol ■ in Fig. 4. Even when the cut-off primary current starts to flow again as the current-blocking transistor 14 turns on, a voltage pulse (2) with a polarity opposite to that during the normal ignition operation is generated on the order of several kilovolts.

This phenomenon actually occurred in earlier high-voltage power distribution type ignition systems that used a distributor, as can be seen from the fact that the basic operation remains the same as described above.

However, in ignition systems using such distributors, the distributor closes the circuit only at the engine rotational position where normal secondary voltage should be applied to the spark plugs, so the reverse voltage caused by this reverse polarity voltage The generation of directional secondary current was essentially disabled.

However, as mentioned above, in an ignition system that uses a low-voltage power distribution type and omits a distributor, this reverse polarity voltage pulse is also applied to the spark plug as it is, and therefore, the reverse polarity voltage (generally positive Unfavorable phenomena such as ignition of the air-fuel mixture due to directional voltage (directional voltage) began to occur.

The present invention basically takes this point into consideration, and in an ignition device configured as a low-voltage distribution type without using a distributor, the present invention substantially blocks the reverse secondary current that occurs at the beginning of the flow of the ignition coil-secondary current. This is an attempt to disclose countermeasures.

Means for Solving the Problems> In order to achieve the above object, the present invention provides an ignition device having the following configuration.

An ignition device for an internal combustion engine of a low-voltage power distribution type that applies a secondary high voltage of an ignition coil directly to the ignition plug of each cylinder without going through a distributor; A high-voltage diode is inserted into the ignition coil secondary closed circuit to block a reverse secondary current that is generated in the opposite direction to that during normal ignition when the primary secondary current begins to flow through the ignition coil. A low voltage distribution type internal combustion engine characterized in that the reverse breakdown voltage of the high voltage diode is set to a value slightly higher than the reverse polarity voltage on the secondary side of the ignition coil that causes the reverse secondary current. ignition device.

<Operations and Effects> As recognized in the above-mentioned summary structure of the present invention, if a diode is provided to block the secondary current in the opposite direction to the normal secondary high voltage, the problem of false ignition caused by this can be solved. .

However, when a diode for blocking a reverse secondary current is provided in this way, there are additional problems that occur.

The reason is that the high voltage diode is generally filled with epoxy resin, etc., but if a gap is created between the coating and the diode part due to thermal stress etc., the creepage insulation deteriorates, and on the other hand, the spark plug may come off in this state. In the case where the secondary side output of the ignition coil is
The problem is that creepage breakdown may occur around the diode with deteriorated insulation.

However, this can be prevented by selecting the reverse breakdown voltage of the diode to be slightly higher than the reverse polarity voltage generated on the secondary side of the ignition coil, as in the above-mentioned configuration of the present invention.

This is because when a high voltage is applied in the reverse direction as described above, the diode breaks down and the voltage across it is therefore clamped to the breakdown voltage. In other words, there is no possibility that an abnormally high voltage remains applied to both ends of the diode, causing dielectric breakdown, and the basic effect of the present invention, which is to suppress the generation of reverse secondary current under normal usage conditions, can be achieved. It can be used without any inconvenience.

Furthermore, from the above mechanism, if the reverse breakdown voltage of the diode satisfies the condition that it is higher than the reverse polarity voltage that occurs when the primary current starts flowing through the ignition coil,
In principle, it can be said that it is desirable to have it as low as possible. However, in general, diodes that are available at low cost and exhibit breakdown characteristics in a high voltage region of several Mv or more are of the avalanche breakdown type, so when using this type,
In relation to the avalanche withstand capacity, it is thought that approximately 5 to 8 KV is actually appropriate.

Embodiments FIG. 1 shows a schematic configuration of a basic embodiment of the present invention. In the figure, the same reference numerals as those in FIG. 3 already described indicate components that may be functionally the same or similar.

The configuration in which the characteristic part of the present invention is expressed in this embodiment is that for the normal secondary voltage generated by the ignition coil IO,
A high-voltage diode 15 is connected to the high-voltage line section 12 on the secondary side of the ignition coil for blocking a reverse secondary current due to a voltage of opposite polarity.
This is what was inserted. The high voltage line portion 12 may be a short wire as described above, or in the case of a type that is attached only to the spark plug 13, it may be a connector portion to the spark plug.

If such a high-voltage diode 15 is provided, first, as explained earlier with reference to Fig. 4, the normal secondary current ■ will not flow normally because this diode 15 is in the forward direction. In contrast to the reverse secondary current that is supplied to the spark plug 13, it is possible to block the reverse secondary current caused by the turn-on of the current blocking transistor 14, thereby preventing accidents such as erroneous ignition in the spark plug 13. can.

However, according to another condition in the gist of the present invention, this high-voltage diode 15 has a reverse breakdown voltage that is slightly higher than the reverse polarity voltage that occurs at the beginning of the flow of current from the ignition coil. To be elected.

The reason for doing so can be explained as follows based on the insulation treatment for the high-voltage diode shown in FIG. 2 and the floating capacitance fi1B shown in phantom lines in FIG.

When the high-voltage diode 15 is provided as described above, the general insulation treatment is to cast a thermosetting resin 16 such as epoxy resin on the high-voltage diode, as shown in FIG.

However, such an insulating coating cannot always guarantee complete adhesion to the outer circumferential surface of the high voltage diode 15, and gaps may occur between the high voltage diode 15 and the resin coating due to thermal stress or the like. , creepage insulation may deteriorate.

On the other hand, if the ignition plug 13 has come off, for example, there may be stray capacitance 16 around the ignition plug or on the secondary side of the ignition coil, as shown by the imaginary line in FIG. If a very high voltage is developed on the secondary side of the ignition coil 10 to give the ignition coil 10, this voltage will charge the stray capacitance 16 with the polarity shown in FIG. In practice, this voltage can be as high as 40 Kv.

Therefore, after this, when the current blocking transistor 14 is turned on again and the next current flows through the ignition coil,
At the beginning, the reverse polarity voltage of several kilovolts generated on the secondary side of the ignition coil has the same polarity as the charge charged in the stray capacitance 16, so it is superimposed on this, and this extremely high voltage is applied to the high voltage diode. 15 as a reverse voltage.

At this time, if there is a gap between the high voltage diode and the coating as described above and the creeping insulation has deteriorated,
A discharge occurs due to this high voltage through the gap, causing an emergency! j
May result in destruction.

However, as in the present invention, this high voltage diode 15 has a voltage slightly higher than the reverse polarity voltage, for example 7Kv.
If the high-voltage diode 15 breaks down at a reverse voltage of approximately clamped at V to 7,
Therefore, there is no need to cause dielectric breakdown.

As the high voltage diode 15 exhibiting a breakdown function on the order of V, an avalanche breakdown type can be obtained at low cost.

As is clear from the above, it is advantageous for the breakdown voltage of the high-voltage diode to be as low as possible as long as it is higher than the reverse polarity voltage. However, when using an avalanche breakdown type diode as described above, In relation to the withstand capacity, in reality, under normal operation, a voltage of about 40 Kv is generated, and when the ignition coil - next current is generated, a reverse polarity voltage of about 5 V is generated. 8
It is appropriate to select it to be about V.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of the main parts of a basic embodiment according to the present invention, Fig. 2 is an explanatory diagram of general insulation treatment of high voltage diodes used in the present invention, and Fig. 3 is a conventional low voltage distribution type ignition device. FIG. 4 is an explanatory diagram of the operation of the ignition system. In the figure, IO is an ignition coil, 11 is a low voltage wiring, 12 is a high voltage line section, 13 is a spark plug, 14 is a current blocking transistor, 15 is a high voltage diode, and 16 is a stray capacitance. Figure 1 Figure 2 155 King Yui Sai-F

Claims (1)

[Scope of Claims] An ignition device for an internal combustion engine of a low-voltage power distribution type that applies a secondary high voltage of an ignition coil directly to the spark plug of each cylinder without going through a distributor; A high-voltage diode is inserted into the ignition coil secondary closed circuit formed by the ignition plug to block the reverse secondary current that occurs in the opposite direction to that during normal ignition when the primary current starts flowing through the ignition coil. and; the reverse breakdown voltage of the high voltage diode is set to a value slightly higher than the reverse polarity voltage on the secondary side of the ignition coil that generates the reverse secondary current; Engine ignition system.