JPH01193080A - Ignition device for engine - Google Patents

Abstract

PURPOSE:To promote combustion so as to suppress exhaustion of HC by independently arranging ignition means around a cylinder on an intake valve side and exhaust valve side and providing an ignition control means for setting a discharge time of the ignition means. CONSTITUTION:An ignition means 11 is arranged on the outer periphery of a cylinder in an circumferential state around a cylinder shaft. The ignition means 11 is independently separated into an intake valve side ignition means 11a and an exhaust valve ignition means 11b. A control unit 17 is set in such a way that the discharge time of the ignition means 11a is longer than that of the ignition means 11b. Thus, it is possible to promote combustion so as to suppress exhaust of HC.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an ignition device for an engine in which ignition means are arranged circumferentially around the outer periphery of a cylinder.

(Prior art) Conventionally, an engine ignition system has one spark plug placed in the cylinder head, and in order to ignite the spark using this spark plug, the fuel mixture near the spark plug is stratified to be richer than in other parts. It is known to improve efficiency by improving ignition characteristics and operating with a lean overall mixture, especially at low loads.

The above stratification can be achieved, for example, by injecting fuel into the intake boat at the end of the intake stroke, completing the fuel supply just before the intake valve closes, and swirling the air-fuel mixture around the cylinder axis. There is a known structural example in which a rich air-fuel mixture is introduced into the cylinder and stratified by unevenly distributing it near a spark plug installed approximately at the center of the cylinder head. (Refer to Publication No. 58-85319)
.

(Problem to be solved by the invention) However, in the above-mentioned ignition performance improvement technology, when a spark plug is provided at the center of the upper part of the combustion chamber and ignition occurs, the flame spreads in a spherical shape and ignites a rich mixture. Even if the ignitability is improved by stratifying the area near the plug, the side wall of the combustion chamber is cooled and the temperature is low, so the flame loses momentum as it spreads around the combustion chamber, disappears midway, and spreads around the cylinder. The combustion of the part is incomplete, and unburned components H are left around the cylinder.
C tends to remain. In response to the rise of the piston, HC around the cylinder is scraped up, and the amount of HC discharged in the latter half of the exhaust stroke increases.

In response to the above point, an ignition means having a plurality of ignition points is arranged circumferentially around the outer circumference of the cylinder around the combustion chamber where the air-fuel mixture is difficult to burn, and this peripheral ignition means promotes combustion of the air-fuel mixture around the combustion chamber. However, an ignition device has been proposed that reduces HC generated around the combustion chamber due to combustion by central single ignition.

However, when a peripheral ignition device like the one above is adopted,
Uniform combustion may not occur due to the temperature distribution corresponding to the air-fuel mixture flow. In other words, when comparing the temperatures on the intake side and the exhaust side of the combustion chamber, the temperature on the intake side is lower due to the inflow of low-temperature fresh air, and if ignition is performed by the same discharge as on the exhaust side, the temperature on the intake side is lower. slows the spread of flame,
Uniform and efficient combustion may not be obtained, and unburned gas may be generated in a portion with low combustibility on the intake side, so that there is a risk that a sufficient HC emission suppressing effect may not be obtained.

In view of the above circumstances, the present invention provides an ignition device for an engine that improves combustibility on the intake side and obtains uniform combustion when ignition is performed by ignition means arranged circumferentially around the outer circumference of the cylinder. The purpose is to

(Means for Solving the Problems) In order to achieve the above object, the ignition device of the present invention has an ignition means disposed on the outer circumference of the cylinder in a circumferential manner centered around the cylinder axis, and the ignition means is placed on the side of the intake valve. The exhaust valve side is provided with an ignition control means that sets the discharge time of the intake valve side ignition means to be longer than the discharge time of the exhaust valve side ignition means.

(Function) In the engine ignition system as described above, ignition is carried out approximately circumferentially around the outer circumference of the cylinder, and multi-point ignition increases the probability of ignition, and the flame propagates from the outer circumference of the cylinder toward the center. The combustion speed becomes faster, and the center receives fast-burning flame from the surroundings, resulting in good combustibility, while the outer periphery is compressed by the combustion of the center, which burns later, and its temperature rises, promoting the oxidation of unburned components. This basically reduces the amount of HC emissions.

Furthermore, the intake valve side ignition means and the exhaust valve side ignition means are formed independently, and the discharge time of the intake valve side ignition means is lengthened to activate the propagation of the ignition flame from the intake side and promote combustion. The aim is to achieve uniform combustion by bringing the combustion closer to the side to eliminate differences in flame propagation, etc., and to further suppress HC emissions in addition to adopting peripheral ignition.

(Example) The present invention will be described in detail below with reference to the drawings.

Embodiment 1 FIG. 1 shows a longitudinal cross-sectional structure of a cylinder portion of an engine equipped with an ignition device according to this embodiment, and FIG. 2 shows a cross-sectional structure of an ignition means portion.

The engine body 1 includes a cylinder block 2 and a cylinder head 3. A piston 5 is housed in a cylinder 2a of the cylinder block 2 so as to be vertically slidable, and a combustion chamber 6 is formed above the piston 5. In the combustion chamber 6, an opening of an intake boat 7 is opened and closed by an intake valve 8, and an opening of an exhaust port (not shown) is similarly connected to an exhaust valve 10 (a second
(Fig.) is opened and closed.

An ignition means 11 is disposed between the coupling surfaces of the cylinder block 2 and the cylinder head 3.

This ignition means 11 has a discharge electrode 13 built into a heat insulating member 12 made of a material having heat insulation and insulation properties such as ceramic, and is formed separately into an intake valve side ignition means 11a and an exhaust valve side ignition means 11b. ing. The heat insulating member 12 has an opening 12a having approximately the same inner diameter as the cylinder 2a.
It has a gasket shape and is sandwiched between the cylinder head 3 and the cylinder block 2. On the other hand, the discharge electrode 13 includes a substantially semicircular intake discharge electrode 13a of the intake valve side ignition means 11a and an exhaust valve side ignition means 11a.
The two discharge electrodes 13a are formed in a substantially circumferential shape with the discharge side discharge electrode 13b having a substantially semicircular shape.

13b is an opening 12a in the cylinder 2a of the heat insulating member 12.
A plurality of (three in the figure) spark gaps G are provided at approximately equal intervals near the inner periphery of each of the spark gaps G, and are connected to separately formed intake and exhaust side ignition sources 15 and 16, respectively.

The ignition timing by the intake valve side ignition means 11a and the exhaust valve side ignition means 11b is controlled by outputting such an ignition signal to a control unit 17 as an ignition control means to the intake side and exhaust side ignition sources 15.16. . The control unit 17 receives inputs such as engine rotational speed signal R1 and intake air amount signal Q, calculates ignition timing according to these operating conditions, outputs an ignition signal at a predetermined timing, and adjusts the discharge time. is outputted differently between the intake side ignition source 15 and the exhaust side ignition source 16, and the discharge time of the intake valve side ignition means 11a is controlled to be longer.

That is, as shown in FIG. 3, the discharge A caused by the intake valve side ignition means 11a is set to start earlier and end later than the discharge B caused by the exhaust valve side ignition means 11b. The discharge time is made longer on the intake valve side.

By lengthening the discharge time of the intake valve side ignition means 11a, the ignition performance on the intake valve 8 side, which has a lower temperature as fresh air is introduced, is improved, and flame propagation is started early due to the early start of discharge. At the same time, by continuing the discharge after ignition, flame growth is promoted to improve the combustibility on the intake valve 8 side, and to match the combustibility on the exhaust valve 10 side to achieve uniform combustion throughout the combustion chamber 6.

Note that when lengthening the discharge time, it may be done by advancing only the discharge start timing or retarding the discharge end timing.

Further, a protrusion 5a that protrudes toward the cylinder head 3 is formed at the center of the upper end of the piston 5, and this protrusion 5a
By this, a squish flow is obtained when the piston 5 rises. In other words, a squish area is formed between the flat bottom surface of the cylinder head 3 and the air-fuel mixture is caused to flow from the center toward the outer circumference near the top dead center of the compression stroke, and the combustion is performed at the ignition position. The air-fuel mixture is collected around the outer periphery of the chamber 6 to improve ignitability, the flow of the air-fuel mixture promotes initial combustion, and the piston 5 enters the explosion stroke.
When the flame begins to fall, a reverse squish phenomenon occurs, causing the flame to flow from the periphery toward the center, promoting flame propagation in the middle and late stages of combustion, increasing the combustion speed, and reducing combustion fluctuations. This is done to ensure more reliable combustibility.

Further, as a structure for obtaining a squish flow, six notches are formed on the circumference of the top of the piston 5 corresponding to the position of the spark gap G of the ignition means 11a, and the other parts are formed as squish parts. Alternatively, a protrusion may be formed on the lower surface of the cylinder head 3 at the central portion excluding the intake port and exhaust port portions to form a squish flow.

Furthermore, by setting the fuel supply direction or supply timing, the fuel in the combustion chamber 6 is unevenly distributed in the periphery and stratified.
The ignition performance may be improved by peripheral ignition.

Furthermore, stratification may be performed by giving a swirl to the intake air flowing into the combustion chamber 6 to cause the fuel to be unevenly distributed in the periphery.

Embodiment 2 This embodiment is shown in FIG. 4, and is an example in which central ignition is used in addition to the peripheral ignition of the previous example.

That is, in this example, the ignition means 11 in the periphery of the cylinder
In addition, an ignition plug 20 similar to the conventional one is disposed in the center of the cylinder head 3, and an ignition source 21 is connected to the ignition plug 20 of the cylinder head 3. A control signal is output to switch the ignition between central ignition and peripheral ignition to improve fuel efficiency as alternator load increases due to increased ignition energy when full-range peripheral ignition is performed.

The rest is the same as the previous example, and the same structures are given the same reference numerals and their explanations will be omitted.

As shown in Figure 5, the change in HC emissions with respect to engine load shows that in the low load range (■), the cooling of the cylinder periphery has a large effect on the reduction in combustibility, resulting in a large amount of HC emissions, while in the medium load range (■), the combustion The amount of HC emissions decreases stably, and in the high load region (3), the amount of HC emissions tends to increase due to the increase in the amount of supplied fuel.

Regarding the above characteristics, in the low load region I, only peripheral ignition is performed as a countermeasure against HC, and in the medium load region ■, only central ignition is performed to reduce the number of ignition points, reduce ignition energy, and reduce the alternator load. In the high load region (■), control is performed to perform both peripheral ignition and central ignition to prevent knocking.

By performing such control, the number of ignition points is reduced without impairing engine drivability, and fuel efficiency is improved.

According to both of the above-mentioned embodiments, the flame propagates from the periphery to the center of the cylinder 2a due to peripheral ignition, so the propagation area becomes much larger than that caused by only central ignition, increasing the combustion speed, and the flame propagates from the peripheral part to the center of the cylinder 2a. It burns well when exposed to fast-burning flame from the surrounding area. In addition, the outer periphery of the combustion chamber is heated by a heat insulating member 12, which prevents the temperature rise caused by being compressed by the pressure of the center, which will be combusted later, and the heat dissipated from the peripheral wall of the cylinder 2a.
By inhibiting combustion, it is possible to keep the temperature high and oxidize unburned components to reduce HC emissions, and the above-mentioned improvement in ignitability and high-speed combustion makes it possible to expand the lean limit and further improve fuel efficiency. .

Additionally, peripheral ignition is formed independently on the intake valve side and exhaust valve side, and the discharge time on the intake valve side is set to be longer than that on the intake valve side, thereby promoting combustion on the intake valve side and burning the entire combustion chamber. This makes it possible to make the HC uniform and further suppress the generation of HC.

(Effects of the Invention) According to the present invention as described above, the ignition means independently formed on the intake valve side and the exhaust valve side are arranged circumferentially on the outer circumference of the cylinder, and the discharge time on the intake valve side is By setting the length longer than the side, it activates the propagation of the ignition flame from the intake valve side and promotes combustion.It approaches the combustion characteristics of the exhaust valve side, eliminates differences in flame propagation, etc., and achieves uniform combustion. The combustion of unburned components in the surrounding area can be further promoted by improving the ignitability and combustion speed by ignition.
This makes it possible to further suppress the discharge of HC.

[Brief explanation of the drawing]

Fig. 1 is a vertical sectional view of the main parts of an engine showing the first embodiment of the present invention, Fig. 2 is a sectional view taken along the line ■-■ in Fig. 1, and Fig. 3 shows an example of setting the discharge time. FIG. 4 is a longitudinal cross-sectional view of main parts of an engine showing a second embodiment of the present invention, and FIG. 5 is a characteristic diagram showing an example of a combination of peripheral ignition and central ignition based on the fluctuation characteristics of HC emission amount with respect to engine load. FIG. 3 is a diagram showing an example of switching control. 1...Engine body, 2...Cylinder block, 2a...Cylinder, 3...
Cylinder head, 6... Combustion chamber, 8...
・Intake valve, 10...Exhaust valve, 11...
...Ignition means, lla...Intake valve side ignition means, 11b...Exhaust valve side ignition means, 1
2...Insulating member, 13, 13a, 13b...
. . . Discharge electrode, G . . . Spark gap, 15.
16... Ignition source, 17... Control unit (ignition control means).

Claims (1)

[Claims] (1) An ignition means is disposed on the outer circumference of the cylinder in a circumferential manner centered on the cylinder axis, and the ignition means is provided independently on the intake valve side ignition means and the exhaust valve side ignition means;
An ignition device for an engine, comprising ignition control means for setting the discharge time of the intake valve side ignition means to be longer than the discharge time of the exhaust valve side ignition means.