JPS599102Y2 - Plasma igniter for internal combustion engines - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a plasma ignition device for internal combustion engines such as automobiles, and more specifically, the ignition gap between the positive and negative electrodes of the ignition plug is surrounded by an electrical insulating material to create a discharge space. Or, it has a spark ignition power source and a plasma ignition power source, and at the ignition timing, the spark ignition power source blows a spark between the electrodes, and the capacitor charged by the plasma ignition power source is discharged in response to the spark. This invention relates to an improvement of a plasma ignition device that performs plasma ignition.

Plasma ignition devices are designed to ensure reliable ignition and improve combustion stability in operating conditions where combustion tends to be unstable, such as in the low-load operating range of internal combustion engines such as automobiles and lean mixture combustion. As an example of an ignition plug used in the above, a ignition plug whose cross-sectional view is shown as 6 in FIG. 1 has been proposed in the past.

The ignition plug 6 has a structure in which the ignition gap between the center electrode 1 and the side electrodes 2 is surrounded by an electrical insulating material 3 such as ceramics to form a discharge space 4 with a small volume. .

The ignition plug 6 is supplied with ignition energy from both a spark ignition power source and a plasma ignition power source, and jets plasma gas generated in the discharge space 4 during spark discharge from the nozzle hole 5 to ignite and burn the air-fuel mixture. let

This ignition plug 6 is different from a normal ignition plug that ignites the air-fuel mixture only by spark discharge. First, a high voltage (10 KV~ 20 KV), and by utilizing the fact that the insulation is broken inside the discharge space 4 at this time, a relatively low voltage (e.g. -3000 V) is generated.
Energy is supplied between the electrodes by discharging the capacitor 12 charged with the plasma ignition power source, and based on the thermal expansion of the resulting high-temperature, high-energy plasma-like gas, high-temperature, high-pressure gas is ejected from the nozzle hole 5. This ensures that the air-fuel mixture is ignited and burned.

In Fig. 1, 7 is a battery power source, 8 is an ignition coil, and 9 is a battery power source.
is a contact point that opens and closes in synchronization with engine rotation, 1
0 is a circuit that generates a high voltage on the secondary side of the ignition coil 8 by turning on and off a built-in transistor according to the opening and closing of the contact point 9; 11 is a power supply for plasma ignition; 12
1 is a capacitor charged by a plasma ignition power source 11 and supplies its discharge energy to the ignition plug 6; 13 is a coil for waveform shaping; and 14 and 15 are diodes for blocking backflow.

By using spark ignition and plasma ignition together in this way, stable combustion can be achieved even during low-load operation where misfires are likely to occur, but on the other hand, because the ignition energy is high, the center electrode 1 is subject to severe wear, and in some cases there is a risk of melting. In particular, if high-energy ignition is continued in the high-speed, high-load region of the engine, power consumption will be extremely large, and the capacity of the battery and alternator, as well as the plasma ignition. Inconveniences arise, such as the need to increase the capacity of the power supply and capacitor.

In order to cope with this problem, a method has been proposed in which the energy supplied per ignition is reduced in the high rotational speed range of the engine, as shown in the characteristic curve a of FIG. 2.

In reality, there is a charging time from the power supply 11 to the capacitor 12, so it is not a simple line, but it is shown as shown in FIG. 2 for the sake of explanation.

That is, in a high-speed, high-load region of the engine, the engine is generally at a high temperature and combustion is stable, so the amount of energy required per ignition is smaller than in the low-speed region.

For this reason, as shown in characteristic curve a in Fig. 2, the amount of energy supplied per ignition is kept constant until the engine speed reaches 240 rpm, but in the high engine speed range beyond that, the amount of energy supplied per ignition is kept constant.
An attempt is made to eliminate the above-mentioned disadvantage by controlling the amount of energy supplied per ignition so that it is inversely proportional to the rotational speed.

However, even if the conventional supply energy control method based on the characteristics shown in FIG. 2a is adopted, the following inconvenience still occurs.

That is, whereas the required amount of energy per ignition varies greatly depending on the engine temperature, the control method shown in FIG. 2a is independent of the engine temperature.

This is because the engine temperature, for example, the radiator water temperature, is controlled to a substantially constant temperature by a thermostat installed at the radiator, so it was thought that it would be meaningless to use a supply energy control system that takes the engine temperature into consideration.

However, in reality, the amount of energy required per ignition varies greatly depending on the engine temperature, especially when starting the engine when the ambient temperature is low and there is a large difference from the radiator water temperature setting (approximately 80°C). The amount of energy required per ignition during warm-up operation from a low temperature is greatly influenced by the engine temperature.

If it is not possible to supply the appropriate amount of ignition energy commensurate with the engine temperature, such as when starting at a low temperature, starting problems may occur or the warm-up time may become longer, resulting in a larger integrated power of ignition energy, which further impairs fuel efficiency. Problems such as deterioration of the condition occur.

The present invention was developed by focusing on these conventional problems, and aims to solve the above problems by detecting the engine temperature and supplying ignition energy commensurate with the detected temperature. The purpose is to provide a plasma ignition device that enables

In order to achieve the above object, the present invention is characterized by providing a temperature detection means for detecting the engine temperature and outputting a signal inversely proportional to the engine temperature, and supplying electric power proportional to the output signal from the temperature detection means to a capacitor. The structure is such that the plasma ignition power source is supplied as charging power to the plasma.

That is, in the characteristic curve representing the energy per ignition shown in Fig. 2, characteristic curve a was conventionally adopted regardless of the engine ambient temperature, but when the ambient temperature is t, t',
t''(t>t'>t''), the energy curve per ignition is changed to a, l), and c in response to the change.

This means that the energy per ignition at a certain rotation speed is inversely proportional to the ambient temperature t, t', t''.
', E''.

An embodiment of the present invention will be explained with reference to FIGS. 3 and 4.

FIG. 3 is a circuit diagram of the embodiment, and FIG. 4 is a time chart of signals of each part for explaining its operation.

In FIG. 3, 11, 12. 15 is the first
The same plasma ignition power source, capacitor, and diode as in the figure are shown.

The plasma ignition power source 11 is constructed as follows.

31 is a pulse output Q with a duty ratio of approximately 50:50.
, Q'.

Q' is the inverted signal of Q.

Reference numerals 32 and 33 designate monostable multivibrator (timer) circuits that are triggered by the rising or falling edge of the pulse signals Q and Q' and output pulse signals having a shorter period than the period of the astable multivibrator 31.

This monostable multivibrator circuit 32. 33, the signal width of the output pulse signal (that is, the time of the timer) is variable by adjusting the resistance value of an external resistor connected between the external terminal and the ground terminal.

34. 35 is a monostable multivibrator circuit 32.
The power transistor is driven by the output of 33 and has a capacity capable of supplying enough power to the primary side of the transformer 36 to sufficiently cover the plasma ignition energy, and has a push-pull circuit structure.

Further, a device having a frequency characteristic capable of turning on and off the oscillation frequency of the unstable multi-by-break 31, for example, a pulse of 10 KHz, is used.

The midpoint of the primary side of the transformer 36 is the battery power supply 7 in Figure 1.
Connected to the positive side of the

Furthermore, the transformer 36 has a voltage of -3000 on the secondary side.
A type that can obtain a high voltage of V, can perform a specified power conversion, and has little conversion loss is selected.

The secondary voltage of the transformer 36 is rectified by a rectifier 37 and charged to the capacitor 12 for plasma ignition.

Reference numeral 16 denotes a temperature-sensitive resistance element, such as a thermistor, which exhibits an electrical resistance value inversely proportional to the engine water temperature, and a monostable multivibrator circuit 32. It is arranged between each of the external terminals 33 and the positive electrode side of the battery power source 7, and changes the signal width of the output pulse signal.

The operation shown in FIG. 3 will be explained using the time chart shown in FIG.

The outputs a, l) of the unstable multivibrator 31 are pulses of a constant period, as shown in the time chart of FIG. 4, and are mutually inverted signals.

Monostable multivibrator circuit 32. Transistors 34 and 33 are each triggered by the falling edge of the human pulse and output pulse wave signals c and d having a time width determined by the resistance value of the thermistor 16, which has a resistance value inversely proportional to the engine water temperature. Drive 35.

Therefore, the currents of the transistors 34 and 35 flow in phase with the signals C and d, supplying power to the primary side of the transformer 36.

Furthermore, the current time width is modulated by the resistance value of the thermistor 16 that detects the engine water temperature.

The power supplied to the primary side of the transformer 36 is the sum of the shaded areas c and d in the time chart of FIG.

The voltage boosted by the transformer 36 is rectified by the rectifier 37 and then charged into the capacitor 12.

Immediately after spark discharge due to the high voltage generated in the ignition coil 8 in FIG. 1, the charge charged in this capacitor is supplied to the ignition plug 6 to generate plasma discharge.

Note that the energy characteristics depending on the engine water temperature are almost the same as thermistor 1.
The selection of the resistance value characteristics of the thermistor 16 is important because it depends on the characteristics of the thermistor 16. If necessary, it is possible to combine a fixed resistor in series and parallel with the thermistor, combine thermistors with different characteristics, or combine it with an active element. etc. will be adopted.

FIG. 5 is a circuit diagram of another embodiment of the present invention, in which a plurality of capacitors 12',
12''... (only 12' is shown and the others are omitted) are connected in parallel to change the capacitance of the capacitor according to the engine temperature, thereby changing the plasma ignition energy.

Each capacitor 12', 12''... is connected in parallel with the capacitor 12 via a relay contact 17,..., respectively.

The plasma ignition power source 11 connects these capacitors 12.
Prepare a battery that can be sufficiently charged even when 12',... are all connected.

Furthermore, it is determined whether or not the thermistor 16 that detects the engine water temperature is below the set value, and if it is below the set value, the transistor 1
A temperature detection circuit 20 that turns on transistor 9 and a relay coil 18 that is excited by turning on transistor 19 are provided.

This excitation of relay coil 18 closes relay contact 17 and connects capacitor 12' to capacitor 12 in parallel.

Since the capacitor 12' is connected in parallel to the capacitor 12, more ignition energy is supplied to the ignition plug 6 than when the capacitor 12 is used alone.

When the engine water temperature is lower, the relay coil and relay contact corresponding to the capacitor 12" are operated by the transistor turned on by the temperature detection circuit corresponding to the capacitor 12" (not shown), and the capacitor 12" is turned on.
FIG. 6 is a circuit diagram showing still another embodiment of the present invention. This embodiment adds control of plasma ignition energy during transient engine operation to the embodiment shown in FIG.

In FIG. 6, 21 is a photo coupler made up of a light receiving element 210 and a light emitting diode 211, 22 is a differential amplifier circuit made up of transistors Tr1 and Tr2, capacitors CI, and resistors R1 to R7, and 23 is a differential amplifier circuit made up of transistors Tr1 and Tr2, capacitors CI, and resistors R1 to R7. It is an idle switch that turns on and turns off when you step on the accelerator.

Since the light receiving element 210 of the photocoupler 21 is connected in series with the thermistor 16 that detects the engine coolant temperature, the resistance change of this light receiving element 210 is transmitted to the monostable multivibrator circuit 32 from the resistance change of the thermistor 16. Equivalently detected.

Now, for example, when you step on the accelerator from idling to driving, the idle switch 23 is switched from on to off, and as a result, the transistor Tr2 limits the current flowing to the light emitting diode 211 for a certain period of time, and the light receiving element 210
The plasma ignition energy is increased by increasing the equivalent resistance of the monostable multivibrator circuit 32 and increasing the time width of the output pulse of the monostable multivibrator circuit 32.

As explained above, according to the present invention, by providing a structure that supplies plasma ignition energy corresponding to the engine temperature, ignition that is appropriate to the temperature can be achieved even during low-temperature startup or warm-up operation at low temperatures. It can supply energy, eliminate inconveniences such as poor starting and long warm-up times, and ensure good combustion at all times.
When the engine temperature is steady, the ignition energy can be lower than before, making it possible to reduce the overall power consumption of the battery power supply.In addition, the present invention is adopted in a system that controls the ignition energy according to the engine speed. In this case, the effect is that combustion is less likely to become unstable during sudden acceleration and deceleration.

In addition to the above-mentioned common effects, according to the embodiment shown in FIG. 5, the circuit structure can be made very simple.
6th. According to the illustrated embodiment, it is possible to achieve the effect that proper combustion can be achieved even during a transient state of operation in which an increase or decrease in instantaneous energy is required.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of a conventional example of a plasma ignition device, Fig. 2 is a characteristic diagram of the relationship between energy per ignition and engine speed, Fig. 3 is a diagram of an embodiment of the present invention, and Fig. 4 3 is a time chart of various signals, and FIGS. 5 and 6 are diagrams of other embodiments of the present invention, respectively. Explanation of symbols, 1... Center electrode, 2... Side electrode, 3
... Electrical insulating material, 4... Discharge space, 5... Nozzle hole,
6... Ignition plug, 7... Battery power source, 8... Ignition coil, 9... Contact point, 11... Power source for plasma ignition, 12... Capacitor, 14. 15
...Diode, 16...Thermistor, 20...
Temperature detection circuit, 21... Photocoupler, 22... Differential amplifier circuit, 23... Idle switch.

Claims (1)

[Scope of utility model registration request] The ignition gap between the positive and negative electrodes of the ignition plug of an internal combustion engine is surrounded by electrical insulating material to form a discharge space, and has a spark ignition power source and a plasma ignition power source. Temperature detection means detects engine temperature and outputs a signal inversely proportional to the engine temperature in a plasma ignition device that performs plasma ignition by emitting a spark between the two and discharging a capacitor charged by a plasma ignition power source in response to the spark. A plasma ignition device for an internal combustion engine, characterized in that the plasma ignition power source is a plasma ignition power source that supplies power proportional to the output signal of the temperature detection means to the capacitor as charging power.