JPH05164030A - Low-tension distribution overlapped discharge type ignition device for internal combustion engine - Google Patents

Abstract

PURPOSE:To provide an ignition device of high practical value adopting a low- tension distribution method and having an overlapped discharge method by superimposing high pressure output of a booster circuit to secondary side high pressure output of an ignition coil accompanying cutoff of a primary electric current by way of switching on a photo-switching element in a photo coupler. CONSTITUTION:Secondary sides of ignition coils 2 are connected to high pressure output of a single booster circuit through a photo-switching element 8 in a photo coupler in series. Thereafter, in accordance with ignition timing of each cylinder synchronously with rotation of an internal combustion engine, a control circuit 4 to sequentially and selectively cut off a primary electric current of a plural number of the ignition coils 2 drives and emits a luminous element 9 of the photo coupler entering the secondary sides of the ignition coils 2 to cut off the primary electric current in accordance with the ignition timing. Consequently, the photo-switching element 8 in the photo coupler is switched on, and the high pressure output of the booster circuit is superimposed to the secondary side high pressure output of the ignition coils 2 accompanying cutoff of the primary electric current.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ignition device for an internal combustion engine having a plurality of cylinders, and more particularly, to an improvement in a low-voltage distribution type ignition device in which each ignition plug for each cylinder is provided with a dedicated ignition coil. ..

[0002]

2. Description of the Related Art A vehicle-mounted ignition device for an internal combustion engine, which is a so-called low-voltage distribution type, is well known.
Prior to that, high-voltage power distribution type, that is, high-voltage output generated on the secondary side of one ignition coil is applied only to the ignition plug of the cylinder whose ignition timing is in accordance with the rotational angle position of the engine. Then
Electromagnetic noise is highly likely to occur, which may cause various electronic devices mounted on the vehicle to malfunction. On the other hand, the low-voltage distribution type does not have such a danger, and the loss of high-voltage energy is small. Further, since the power is distributed on the primary side of the ignition coil, it is easy to control electronically, and since mechanically moving parts such as a conventional distributor are not required, the failure probability is greatly reduced and maintenance is easy. Such an advantage more than compensates for the inconvenience of requiring a dedicated ignition coil for each spark plug.

In fact, recently, such a low-voltage distribution type ignition device is becoming the mainstream, but it has been desired to further use a so-called overlapping discharge system in addition to this system. This is because when a high voltage is generated on the secondary side of the ignition coil due to the interruption of the ignition coil primary current, the high voltage boosted by a separately provided booster circuit is additively superimposed on the secondary voltage. In combination with the high-voltage power distribution system, many ignition devices including such a system have been proposed.

[0004]

However, the combined use of the high-voltage power distribution system and the lap discharge system is very inefficient because of a large energy loss. Further, for the reasons described above, it is expected that the high-voltage distribution system itself will continue to decline in the future, so it is no longer a good idea to intentionally improve such a system. In other words, there is an urgent need to provide an igniter that has a low-voltage distribution system and also has a lap discharge system. Further, such an ignition device must be a mode that can be sufficiently realized even with the current technology, and must be as small as possible and can be provided at a low cost. The present invention has been made in view of this point, and it is an object of the present invention to provide an ignition device having a high practical value that employs a low-voltage distribution system and has a lap discharge system as an ignition device for an internal combustion engine having a plurality of cylinders. is there.

[0005]

In order to achieve the above object, the present invention provides a low-voltage distribution type ignition device, that is, an ignition device in which each ignition plug has its own ignition coil. , The optical switching element of each photo coupler is connected in series to the high voltage output of a single booster circuit, and the light emitting element in each photo coupler is driven and emits light in synchronization with the cutoff timing of the ignition coil primary current. I chose However, in another aspect of the invention,
Of the multiple cylinders, the secondary side of the pair of ignition coils for the pair of cylinders, in which the other is in the exhaust process when one requires ignition, is not dedicated to each but has a common photocoupler. We also propose an ignition device that is connected in series to the high-voltage output of the booster circuit.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows an embodiment of the present invention.
In the illustrated case, the low-voltage distribution type ignition device for a four-cylinder vehicle is illustrated as being modified according to the present invention. Therefore, there are four spark plugs in total and four ignition coils dedicated to each. Hereinafter, when each spark plug or ignition coil is specifically shown, reference numerals with suffix 1 _-1 , 1, _-2 , 1 _-3 , 1 _-4 ; 2 _-1 , 2 _-2 , 2 _-3 , 2
_-4 is used, but in the case where any one can represent the other, the suffix is omitted and, for example, simply referred to as an ignition plug 1 or an ignition coil 2. This also applies to the constituent elements represented by other suffix codes.

This embodiment has the same components as those of the ordinary low-voltage distribution type ignition device, and these components need not be modified. That is, based on the engine rotation angle signal 3 obtained from a suitable known existing sensor means (not shown), the control circuit 4 has a total of four ignition coil primary current interruption switching elements 5 ,. Medium, by turning off the switching element 5 that is serially connected to the primary circuit of the ignition coil 1 for the cylinder that has reached the present ignition timing,
Due to the mutual induction principle, a high voltage output is generated on the secondary side of the ignition coil. The switching element 5 is npn in the illustrated case.
Although it is shown by the transistor 5, any so-called power switching element may be used, and there are also usage examples of a power MOSFET, a thyristor and the like. The present invention is also not particularly limited.

The components added by the present invention and their operations will be described below with reference to the waveform diagram of the main part of FIG. First, for the ignition coil 2 approaching the ignition timing, an ON command is given from the control circuit 4 to the switching element 5 that selectively interrupts the primary current, and as shown in FIG. A primary current is made to flow to the device to store energy.

However, when the switching element 5 which is once turned on in this way reaches the ignition timing of the cylinder related to the switching element and a turn-off command is given from the control circuit 4, the switching element 5 is turned on.
The primary current of the ignition coil 2 in which the primary circuit is connected in series is suddenly cut off, and an induced high voltage is generated on the secondary side thereof. In the conventional ignition device which is intended to obtain the discharge energy only by the mutual induction principle by such current interruption without adopting the overlapping discharge method which the present invention is trying to achieve, the discharge current obtained by the spark plug 1 is used. The waveform is
In the waveform named “ignition plug combined discharge current” in FIG. 2, as shown by the waveform of the phantom line, for example, the peak current value of the rising is a typical value of about 60 mA, but the duration is sufficient. Was short, and typically only a waveform of about 1.8 mS was obtained.

However, in the present invention, a large discharge energy can be obtained for a long time by the following circuit configuration and operation. First, in terms of circuit structure, the ground side terminal of the secondary winding of each ignition coil 2 is a photocoupler composed of a light emitting element 9 and an optical switching element 8 and is connected to the booster circuit of the booster circuit via the optical switching element 8. Connected to high voltage output. In the illustrated case, the booster circuit includes a booster transformer 11, a switching element 12 that choppers the primary side of the booster transformer, a rectifying diode 13 that rectifies a secondary high-voltage output, and a smoothing capacitor 14. It is driven by the oscillation drive circuit 10 as described later. As is well known, in this type of ignition device, since the ground side is positive with respect to the discharge current, the polarities of the respective components are determined so that the high voltage output of the booster circuit can also generate a large voltage in the negative direction. The connection point between the anode of the rectifying diode 13 and the negative terminal of the smoothing capacitor serves as the high voltage output terminal of the booster circuit.

There are various types of photocouplers available on the market, and in general, the light emitting element 9 is common in that it is a light emitting diode, but when it receives the light output from this light emitting diode, it transitions to the ON state. Optical switching element 8
In addition to the most common phototransistors, there are photothyristors and phototriacs. Either of these is acceptable, so they are simply indicated by switch symbols in the figure.
Incidentally, in the experimental example of the applicant, a photocoupler using a phototriac was used as the optical switching element 8. Therefore, once it is triggered by the light emitting element 9, it remains on until the triac element current drops below a predetermined value.

In the illustrated case, the light emitting elements 9 _{-1 to} 9 _-4 of each of the four photo couplers are selectively driven by dedicated light emitting element drive circuits 15 _-1 to 15 _-4 . .. Each light emitting element drive circuit 15 is an inverter and a monostable multivibrator (in the figure, abbreviated as "OSM") so as to be triggered at the moment when a switching element for cutting off the ignition coil primary current is turned off. , The output of the monostable multivibrator OSM rises at the timing when the base voltage of the current cut-off transistor 5 falls, and the light-emitting element 9 in the corresponding photocoupler is driven for a prescribed time, and the optical switching element 8 is turned on.

Further, in addition to the basic function of the conventional ignition device described above, the control circuit 4 temporarily controls any of the four current interruption transistors 5 _{-1 to} 5 _-4. After being turned on and then rapidly turned off, a command signal for driving the oscillation drive circuit 10 is issued with a slight delay. As a result, the oscillation drive circuit 10 oscillates a pulse train having a predetermined frequency for a predetermined period, and the switching element 1 responds to the oscillation pulse.
2 turns on and off in a fine cycle. In the case shown in the figure, the switching element 12 is composed of a MOS transistor (not limited, of course), but this ON / OFF operation connects one end to the hot side of the battery 6 via the connection node A in the figure. The primary current flowing through the primary winding of the boosting transformer undergoes chopper ringing.
High-voltage output appears on the secondary side according to the primary and secondary winding ratios.

Due to such a circuit configuration, when the primary current of the ignition coil 2 at the ignition timing in FIG. 2 is cut off by the control circuit 4, a high voltage output is generated on the secondary side of the ignition coil. At the same time, the light emitting element 9 in the photocoupler for the ignition coil is also driven to emit light,
As a result, the corresponding optical switching element 8 is also turned on, and the secondary ground side terminal of the ignition coil 2 is connected to the high voltage output of the booster circuit (negative terminal of the capacitor 14). Therefore, the optical switching element 8 that was initially turned on
And smoothing capacitor 14 of booster circuit, and spark plug 1
With a closed loop including the above, the spark plug 1 can obtain a discharge current waveform that sharply rises, just like the conventional current interruption type ignition device.

However, after that, when the oscillation drive circuit 10 starts to operate by the signal from the control circuit 11 at a timing slightly delayed by the scheduled time, the primary side of the step-up transformer 11 receives the chopper ring by the switching element 12, A high voltage output appears on the secondary side of the transformer, which is rectified by the rectifying diode 13 and superposed on the discharge current generated by the current cutoff mechanism,
As shown in FIG. 2, the combined discharge current of the spark plug 1 can maintain a high energy level for a long time sufficient for fuel ignition. This period is approximately 5 mS in the prototype of the present inventor, and 40 mA during that period.
A discharge current of a certain degree can be continuously obtained. In fact, the discharge spark in the spark plug 1 greatly improves the ignitability of the fuel, which in turn contributes to fuel consumption. However, of course, the determination of the discharge duration is a matter left to the optimum design to be made for each vehicle.

Further, as is apparent, according to the principle of the present invention, the booster circuit may always be in operation, but this is a waste of energy. Therefore, as seen in the illustrated embodiment, it is desirable to be driven only when needed.

The circuit shown in FIG. 1 can be further simplified as shown in FIG. For example, in the case of a four-cylinder car with four cycles being driven, if a cylinder is in the compression process, it is in the exhaust process, and if it is in the intake process, it is in the explosion process. Each can be divided into two pairs of cylinders. When one of the paired cylinders receives ignition near the end of the compression process, even if an ignition spark occurs in the other cylinder in the exhaust process, there is no problem.

Therefore, in the embodiment shown in FIG.
The secondary ground side terminals of the ignition coils (2 _-1 , 2 _-4 ), (2 _-2 , 2 _-3 ) for the pair of cylinders having such a relationship are
Optical switching element 8 of common photo coupler
_-14 , _8-23 , and when any one of the ignition coils 2 of the paired cylinders is at the ignition timing, the light emitting elements _9-14 , _{9-23 in} those photocouplers are connected.
Are configured to be driven. That is, the number of the light emitting element drive circuits 15 is also reduced to two (15 _-14 , 15 _-23 ) as compared with the embodiment shown in FIG. 1, and the primary current of the ignition coils of the paired cylinders. Each light-emitting element drive circuit 1 is connected through the OR circuits 16 and 16 that take the OR of the base voltages of the cut-off switching elements (5 _-1 , 5 _-4 ), (5 _-2 , 5 _-3 ).
_5-14 and _15-23 are designed to be driven. Such external OR circuits 16 and 16 are for the purpose of explanation, and are often unnecessary in practice, and in the case of the embodiment shown in FIG. 1, the signal is taken out from an appropriate portion in the control circuit 4. In comparison with the above, each light-emitting element drive circuit 15 has a double cycle.
_-14 , _15-23 can be assembled so that they are driven sequentially.

Next, considering a slightly practical problem,
In the photocouplers currently on the market, the withstand voltage of the optical switching element 8 is at most 500 to 600V. On the other hand, the output of the ignition coil secondary side due to the initial current interruption mechanism before the booster circuit is activated can easily reach several Kv. Therefore, if there is a concern about pressure resistance, it is advisable to devise as shown in FIG. FIG. 4 shows only one ignition coil and shows only a portion related to the peripheral circuit thereof, but the point is that a capacitor Cs having an intentionally appropriate capacitance is provided in parallel with each optical switching element 8 of each photocoupler. To connect. The reason why the voltage applied to each optical switching element 8 is reduced in this way is as follows.

Generally, regarding the secondary side of the ignition coil 2,
As a combined capacity of the secondary side capacity of the ignition coil and the capacity of the ignition plug 1, a stray capacity Cf as shown in FIG. 4 in an equivalent circuit is expected. Therefore, if a capacitance Cs is intentionally connected in parallel to each optical switching element 8, a capacitance voltage dividing circuit can be equivalently configured, and when the ground side voltage Vo of the optical switching element 8 is set, the optical switching is performed. The voltage Vt applied across the element 8 is Vt = {Cf / (Cs + Cf)} Vo. Therefore, if the capacitance value of the capacitor Cs connected in parallel is increased to a certain extent or more within a range that does not actually cause a problem such as a response delay of the optical switching element 8, the voltage applied to both ends of the optical switching element 8 is considerably small. It can be clamped below the voltage value, and the existing photocoupler can be sufficiently used.

[0021]

According to the present invention, in the low-voltage power distribution type ignition device, the overlapping discharge system can be significantly used together. For example, if a dedicated step-up transformer is used for each ignition coil, the circuit becomes simple, but it becomes too large and effective, which is not practical. On the other hand, according to the present invention, only one step-up transformer needs to be used. Further, when the boosted output is selectively applied to the secondary side output of the ignition coil at the ignition timing, the high voltage side that is the switching line for that and the low voltage side that is the command line that drives this are the photocoupler Since it is completely electrically separated by adoption, the circuit becomes very simple, and a rational control system can be constructed by using an electronic circuit that controls the primary low-voltage current of each ignition coil. it can. Since the low-voltage power distribution system is a very promising system in the future, the present invention allows the advantages of the lap discharge system to be added to the system to improve fuel ignitability and fuel efficiency. It is highly desirable for the development of this kind of field to obtain the reduction effect of.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a low voltage distribution overlapped discharge ignition device of the present invention.

FIG. 2 is an explanatory diagram showing main waveforms for explaining the operation of the circuit shown in FIG.

FIG. 3 is a circuit diagram of a second embodiment of the present invention.

FIG. 4 is an explanatory diagram showing an improvement for reducing an end-to-end voltage that can be applied to the optical switching element of the photocoupler used in the present invention.

[Explanation of symbols]

1 spark plug, 2 ignition coil, 4 control circuit, 5 primary current cutoff transistor, 6 vehicle battery, 8 optical switching element in photocoupler, 9 light emitting element in photocoupler, 10 oscillation drive circuit, 11 step-up transformer , 12 step-up transformer switching element for primary current chopper ring, 13 rectifying diode, 14 smoothing capacitor, 15 light emitting element drive circuit in photo coupler, Cs capacitor connected in parallel with optical switching element.

Claims (3)

[Claims] 1. A low-voltage distribution-type ignition device for a multi-cylinder internal combustion engine, wherein a dedicated ignition coil is used for each ignition plug for each cylinder; a secondary side of each ignition coil;
The optical switching element of the photocoupler is connected in series to the high voltage output of a single booster circuit; the primary currents of the plurality of ignition coils are synchronized with the rotation timing of the internal combustion engine according to the ignition timing of each cylinder. The control circuit for selectively selectively shutting off the primary current also drives the light emitting elements of the photocoupler in series on the secondary side of the ignition coil for shutting off the primary current so as to emit light in accordance with the ignition timing. Turning on the optical switching element in the coupler and superimposing the high-voltage output of the booster circuit on the secondary-side high-voltage output of the ignition coil due to the interruption of the primary current; Ignition device. 2. The ignition device according to claim 1, wherein among the plurality of cylinders, a pair of ignition coils for a pair of cylinders are in a relationship that when one of them requires ignition, the other is in an exhaust process. The secondary side is connected to the high-voltage output of the booster circuit via a common photocoupler; 3. The ignition device according to claim 1, wherein each optical switching element of each photocoupler comprises:
Ignition device characterized by connecting capacitors in parallel.