JPH01187356A - Combustion controller for engine - Google Patents

Abstract

PURPOSE:To make improvements in combustibility at the time of idling by installing each exhaust control valve in plural exhaust parts, and forming its passage diameter to be relatively smaller, in a device which makes a part of exhaust gas flow backward to a combustion chamber from one of four exhaust ports at time of the intake stroke. CONSTITUTION:Intake and exhaust ports 7, 8 and 9, 10 being opened or closed each by intake and exhaust valves 3, 4 and 5, 6 are opened each cylinder 2 of an engine 1, and these intake ports 3, 4 and exhaust ports 9, 10 are connected each to common suction and exhaust passages 12, 13. A throttle valve (unillustrated herein) is installed in this suction passage 12, while suction and exhaust valves 15, 16 are installed each in the second exhaust ports 8, 10. In addition, the second exhaust port 10 is formed into a small diameter as compared with the first exhaust port 9, while the second exhaust valve 6 sets a valve overlap period with the suction valve to be larger and thereby exhaust gas is made introducible to a combustion chamber at an intake stroke, so that an exhaust gas quantity at that time is made free of adjustment by the exhaust control valve 16.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an engine combustion control device, and in particular to an EGR
One method for (exhaust gas recirculation) is a method in which a part of the exhaust gas flows directly back into the cylinder from the exhaust port.

(Prior art) EGR, which is a method of backflowing (sucking back) an appropriate amount of exhaust gas directly from the exhaust port to the cylinder, is called internal EGR, as opposed to a normal EGR device that uses an exhaust gas recirculation passage. .

Conventional technology regarding internal EGR is, for example, disclosed in Japanese Patent Application Laid-open No. 1983
It is disclosed in the publication No.-112814. In this conventional technology, a valve timing mechanism is provided that changes the closing timing of the exhaust valve so that it is delayed in a low load range, and the closing timing of the exhaust valve is delayed to increase the valve overlap period with the intake valve. , a part of the exhaust gas that exited to the exhaust port side flows back into the cylinder at the beginning of the intake stroke, and internal EGR
This is what you get.

In the internal EGR mentioned above, the temperature of the exhaust gas brought into the combustion chamber is higher than in normal EGR, so the volume is larger even at the same EGR rate, and the amount of fresh air inflow is reduced accordingly, so the opening of the throttle valve is becomes larger, reducing pumping loss and improving fuel efficiency. In addition, the inflowing fuel is affected by high-temperature exhaust gas, promoting its vaporization, improving combustibility, and reducing the amount of unburned components released.
This has the advantage of improving emission performance.

(Problem to be Solved by the Invention) However, in the prior art as described above, the EGR rate is adjusted by changing the closing timing of the exhaust valve and changing the valve overlap period. It is difficult to control the EGR rate with high precision by adjusting the overlap period, and the variable valve timing mechanism is complicated and expensive.

In response to the above points, multiple exhaust valves are provided in one cylinder,
It is conceivable to set a large overlap period by delaying the closing timing of one exhaust valve, provide an exhaust control valve at the exhaust port corresponding to this exhaust valve, and adjust the EGR rate by opening and closing the exhaust control valve. In other words, when the uF air control valve is open, the uF air gas discharged to this exhaust port is sucked back into the combustion chamber during the overlap period, and the larger the opening of the exhaust control valve, the higher the EGR rate. If it becomes high and closed, the EGR rate will decrease.

However, as mentioned above, the internal E
In a combustion control device that is equipped with an exhaust control valve that adjusts the GR rate, the exhaust control valve is turned off to cut internal EGR when idling, but exhaust gas remains in the exhaust port up to this exhaust control valve. , this portion of exhaust gas flows into the combustion chamber at the time of overlap and becomes internal EGR. In other words, even when the exhaust control valve is closed, high-pressure exhaust gas flows into the exhaust port between the exhaust valve and the exhaust control valve when it opens, and flows back into the combustion chamber during the overlap period when the combustion chamber pressure decreases. This results in internal EGR, which further reduces combustibility in addition to the already low combustibility at idle, which poses a problem in ensuring idling stability.

Therefore, in view of the above circumstances, the present invention provides an engine combustion system that reduces the internal EGR rate at the time when the exhaust control valve is closed to ensure drivability, and that improves combustibility and fuel efficiency through internal EGR. The purpose of this invention is to provide a control device.

(Means for solving the problem) In order to achieve the above object, the combustion control device of the present invention has a plurality of exhaust valves in each cylinder, and for at least one of them, the valve overlap period with the intake valve is increased. Set the valve overlap period to introduce exhaust gas into the combustion chamber from the exhaust port into the combustion chamber, and adjust the amount of exhaust gas introduced into the combustion chamber into the exhaust port corresponding to the exhaust valve with a large valve overlap period. In addition to providing a control valve, the exhaust port provided with the exhaust control valve is configured to have a smaller diameter than other exhaust ports.

(Function) In the engine combustion control device as described above, when the exhaust control valve is closed during idling, etc., the exhaust port for the exhaust control valve has a small diameter and a small volume, and the exhaust gas flowing in and out is By reducing the amount, the internal EGR rate decreases and improves combustion stability. On the other hand, when the exhaust control valve is opened, the EGR rate is adjusted with a simple structure and with high precision according to the opening degree. .

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

Figure 1 shows each cylinder of the engine? 1. Indicates formation.

Each cylinder 2 of the engine 1 has a first intake port 7 opened and closed by a first intake valve 3, a second intake port 8 opened and closed by a second intake valve 4, and a second intake port 8 opened and closed by a first exhaust valve 5. The first exhaust port 9 and the second exhaust port 10, which is opened and closed by the second exhaust valve 6, are connected to each other. Both intake ports 7.8 are connected to a common intake channel 12, and likewise both exhaust ports 9.10 are connected to a common exhaust channel 13.

A throttle valve (not shown) is installed in the intake passage 12 to control the intake flow rate, while an intake control valve 15 is installed in the second intake port 8, and an intake control valve 15 is installed in the second exhaust port 10. An exhaust control valve 16 is installed. Further, the second exhaust port 10 is formed to have a smaller diameter than the first exhaust port 9.

The first and second intake valves 3 and 4 and the first and second exhaust valves 5 and 6 are opened and closed by a known valve mechanism, and the opening and closing timings thereof are shown in FIG.

First, the first exhaust valve 5 opens at EO, and after top dead center TDC, the first exhaust valve 5 opens at EO.
Close with C1. Further, like the first exhaust valve 5, the second exhaust valve 6 opens at EO and closes at a time EC2 later than the closing time EC1 of the first exhaust valve 5. On the other hand, the first intake valve 3 is at the top dead center TD.
It opens at 101 near C and closes at Ic. Further, the second intake valve 4 is opened at a timing lO2 earlier than the opening timing 101 of the first intake valve 3.
Similarly to the first intake valve 3, it is closed by the IC.

Further, the intake control valve 15 and the exhaust control valve 16 are respectively opened and closed by actuators 17 and 18,
The operation of the actuators 17, 18 is controlled by control signals from the control unit 19 depending on the operating state. In order to detect the operating state of the engine 1, the control unit 19 receives an engine rotation signal from a rotation sensor 20, a load signal from a negative pressure sensor 21 installed in the intake passage 12, which detects intake negative pressure, etc. Each is manually powered.

In addition, from the point of view of reducing the volume of the second exhaust port 10, it is preferable to install the exhaust control valve 16 as close to the second exhaust valve 6 as possible, but if it is placed too close, the temperature will increase. Since this is disadvantageous in terms of reliability, for example, a shutter valve type on-off valve may be installed in the vicinity of the cylinder head of the exhaust manifold.

As shown in FIGS. 3 and 4, the control unit 19 controls the exhaust control valve 1 in accordance with the load and the engine speed.
6 is opened to perform exhaustion at the opening/closing timing of the second exhaust valve 6 (late closing), while the intake control valve 15 is closed and intake is performed at the opening/closing timing of the first intake valve 3 (late opening). In addition, at other times of idling and at low speed and high load, that is, in the EGR cut region, the exhaust control valve 16 is closed and exhaust is performed at the opening/closing timing (early closing) of the first exhaust valve 5, while the intake control valve 15 is opened and the first exhaust valve 5 is opened/closed. This control is performed so that the intake valve 4 takes in air at the opening/closing timing (early opening) of the intake valve 4. This control can be easily implemented using the same method as general engine electronic control using a microcomputer, so it will not be described in detail in this specification.

Next, the effect of the above configuration will be explained. First, in the EGR region, since the exhaust control valve 16 is opened as described above and exhaust is performed at the opening/closing timing (late closing) of the second exhaust valve 6, the overlap period after top dead center TDC becomes longer. As a result, while the second intake valve 4 opens and the piston descends past the top dead center, as the pressure inside the cylinder 2 decreases,
Immediately before the second exhaust valve 6 closes, the exhaust gas in the second exhaust port 10 is sucked back into the cylinder 2 so as to flow back into the cylinder 2. At this time, the amount of exhaust gas that flows backward and returns into the cylinder 2 changes depending on the opening degree of the exhaust control valve 16 of the second exhaust port 10, and the larger the opening degree, the greater the amount of exhaust gas introduced. As a result, the combustibility and fuel efficiency of internal EGR can be improved several times.

Furthermore, in the above EGR region, the intake control valve 15 is closed and intake is performed at the opening/closing timing (late opening) of the first intake valve 3, so that the intake air actually flows into the cylinder 2 after the piston has descended considerably. However, the exhaust gas that has been introduced into the cylinder 2 up to that point is located on the piston side, and the intake air flows into the upper layer of the piston, resulting in stratification. As a result, the flammable air-fuel mixture is unevenly distributed around the spark plug to improve ignitability, and the internal EGR function is ensured under the thermal influence of exhaust gas.

On the other hand, in the EGR cut region, the exhaust control valve 16 is closed to perform exhaust at the opening/closing timing of the first exhaust valve 5 (early closing), and the intake control valve 15 is opened to perform the opening/closing timing of the second intake valve 4 (early opening). ), the overlap period after top dead center TDC is shortened and the amount of intake air is ensured. By shortening this overlap period, the amount of exhaust gas remaining in the cylinder 2 is reduced when transitioning from the exhaust stroke to the intake stroke. At that time, even if the exhaust control valve 16 is fully closed to cut the internal EGR, the second
When the exhaust valve 6 opens, high pressure exhaust gas flows into the exhaust control valve 1.
6 and flows back into the cylinder during the overlap period when the cylinder pressure decreases, resulting in internal EGR.
Since the diameter of 0 is made small to reduce the volume,
The amount of exhaust gas remaining in the second exhaust port 10 is reduced to ensure combustion stability when the exhaust control valve 16 is fully closed, especially when idling.

In the above embodiment, the two intake valves 3.4 and the intake control valve 15 are arranged, and the intake timing is also changed in accordance with the EGR region to obtain stratification. , this is not essential and the timing may not be changed and intake air may be introduced by one intake valve.

Furthermore, in the above embodiment, EGR is cut in a high load region, but this is done to prevent knocking, since an increase in intake air temperature caused by exhaust gas tends to cause knocking. In an engine that performs supercharging, the exhaust control valve 16 may be opened. On the other hand, the second exhaust port 10 upstream of the exhaust control valve 16 of each cylinder 2 in a multi-cylinder engine may be communicated through a communication path to improve the distribution of exhaust gas between cylinders.

(Effects of the Invention) According to the present invention as described above, the valve overlap period with the intake valve is set to be large for one of the plurality of exhaust valves for the cylinder, and the valve overlap period with the intake valve is set to be large. While introducing υ gas from the exhaust port, an exhaust control valve for adjusting the amount of exhaust gas introduced into the combustion chamber is provided at the exhaust port corresponding to the exhaust valve with a large valve overlap period. By configuring the diameter of the exhaust port provided with the control valve to be smaller than other exhaust ports, when the exhaust control valve is closed, such as when idling, the exhaust port for this exhaust control valve has a small diameter. , its volume is small, and by reducing the amount of exhaust gas flowing in and out, it lowers the internal EGR rate and improves combustion stability, ensuring good drivability. It is possible to adjust the EGR rate with a simple structure and with high accuracy depending on the situation.

[Brief explanation of the drawing]

Fig. 1 is a conceptual diagram of an engine combustion control device according to an embodiment of the present invention, Fig. 2 is a characteristic diagram showing an example of valve timing settings, and Fig. 3 is an example of opening/closing control of exhaust and intake control valves depending on the load. FIG. 4 is a characteristic diagram showing an example of opening/closing control of exhaust and intake control valves with respect to engine speed. 1...Engine, 2...Cylinder, 5.6
...Exhaust valve, 9.10...Exhaust port, 13...Exhaust passage, 16...Exhaust control valve, 19...Control unit. Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] (1) Each cylinder has multiple exhaust valves, and at least one of them has a large valve overlap period with the intake valve to introduce exhaust gas from the exhaust port into the combustion chamber into the intake stroke. An exhaust control valve that adjusts the amount of exhaust gas introduced into the combustion chamber is provided at the exhaust port corresponding to the exhaust valve with a large overlap period set, and the diameter of the exhaust port equipped with the exhaust control valve is set to the other exhaust port. An engine combustion control device characterized by being set smaller than.