JPH04183921A - Internal combustion engine - Google Patents

Abstract

PURPOSE:To shorten the temperature rise time of a catalyst and reduce an exhaust amount of noxious components by increasing flow resistance of an exhaust path to raise the temperature of exhaust gas when a catalyst tempera ture is under a predetermined temperature. CONSTITUTION:A catalyst 5 is provided in an exhaust pipe 3 of an engine body 1, and an exhaust muffler 6 is provided in the exhaust pipe downstream of the catalyst 5. Then, an exhaust controlling valve 7 is provided in the exhaust pipe 3 between the catalyst 5 and exhaust muffler 6 to control the flow resistance of the exhaust pipe 3. Also, the exhaust controlling valve 7 is controllably opened and closed by an actuator 8. When a conduit 9 is adapted to communicate to a negative pressure pipe 11, negative pressure is introduced into a negative pressure chamber 8b of the actuator 8 to drive the exhaust controlling valve 7 in the valve opening direction and increase the flow resistance of the exhaust pipe 3. A change-over valve 10 is controlled through a drive circuit 30 by an electronic control unit 20 on the basis of a detecting signal of a temperature sensor 40 for detecting the temperature of the catalyst 5.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an internal combustion engine capable of stratified combustion.

[Conventional technology]

Equipped with a fuel injection valve to directly inject fuel into the combustion chamber, fuel is injected in the latter half of the compression stroke at low loads,
An internal combustion engine is known that performs so-called stratified combustion, in which fuel is injected during the intake stroke and the latter half of the compression stroke when the load is high (see Japanese Patent Laid-Open No. 2-169834).

[Problem to be solved by the invention]

By the way, the catalyst provided in the exhaust passage does not act as a catalyst when the temperature is lower than a predetermined temperature, and therefore cannot remove harmful components in the exhaust gas.

In the above-mentioned internal combustion engine, the amount of intake air is excessive due to stratified combustion, and therefore the exhaust gas temperature is low.

Therefore, it takes a relatively long time to heat the catalyst above a predetermined temperature, which causes the problem that the catalyst does not function during this time and a large amount of harmful components are released into the atmosphere together with the exhaust gas. arise.

[Means to solve the problem]

In order to solve the above problems, according to the present invention, in an internal combustion engine that includes a catalyst in the exhaust passage and is capable of stratified combustion, a resistance changing means for changing the flow path resistance of the exhaust passage is provided in the exhaust passage downstream of the catalyst. When the temperature of the exhaust passage is lower than a predetermined temperature, the resistance changing means increases the flow resistance of the exhaust passage.

[For production]

When the temperature of the catalyst is lower than a predetermined temperature, the flow resistance of the exhaust passage is increased by the resistance changing means.

As a result, the exhaust pressure increases and the amount of intake air decreases, causing the exhaust gas temperature to rise.

〔Example〕

Referring to FIG. 1, 1 is the engine body, 2 is an intake pipe, and 3 is an exhaust pipe. A throttle valve 4 is arranged in the middle of the intake pipe 2. This throttle valve 4 is controlled to open and close by a motor 45, and is kept substantially fully open except during idle operation and deceleration operation. A catalyst 5 is provided in the exhaust pipe 3, and an exhaust muffler 6 is provided in the exhaust pipe 3 downstream of the catalyst 5. The exhaust pipe 3 between the catalyst 5 and the exhaust muffler 6 is provided with an exhaust side control valve 7 for controlling flow path resistance of the exhaust pipe 3. The exhaust control valve 7 is controlled to open and close by an actuator 8. The actuator 8 is divided into a negative pressure chamber 8b and an atmospheric pressure chamber 8C by a diaphragm 8a, and the diaphragm 8a is urged toward the atmospheric pressure chamber 8C by a compression coil spring 8d. Diaphragm 8a is connected to exhaust control valve 7 via rod 8e. The negative pressure chamber 8b is connected to the first port HOa of the □ switching valve 10 via a conduit 9. A second port 10b of the switching valve 10 is connected to a negative pressure tank 12 via a negative pressure pipe 11, and the negative pressure pipe 11 is connected to a negative pressure pump 13.

A third port 10c of the switching valve 10 is connected to an air cleaner (not shown). When the conduit 9 is brought into communication with the air cleaner, the atmosphere is introduced into the negative pressure chamber 8b and the exhaust control valve 7
is considered to be fully open. On the other hand, when the conduit 9 is brought into communication with the negative pressure pipe 11, negative pressure is introduced into the negative pressure chamber 8b, and therefore the exhaust control valve 7 is driven in the valve closing direction, and the flow path resistance of the exhaust pipe 3 is increased. .

The electronic control unit 20 consists of a digital computer and a ROM connected to the Japanese-style room by a bidirectional bus 21.
(read only memory) 22, RAM (random access memory) 23, CPU (microprocessor) 24
, a human-powered boat 25 and an output port 26. A temperature sensor 40 that detects the temperature of the catalyst 5 is connected to the A'D converter 2.
7 to the input port 25. An air-fuel ratio sensor 41 that is arranged in the exhaust pipe 3 upstream of the catalyst 5 and detects the air-fuel ratio.
is connected to the human-powered boat 25 via an AD converter 28. An idle switch 42 that detects the idle opening degree of the throttle valve 4 is connected to the input port 25. A crank angle sensor 43 for detecting engine speed is connected to input port 2.
Connected to 5. An accelerator opening sensor 44 for detecting the amount of depression of an accelerator pedal (not shown) is connected to the input port 25 via an AD converter 29.

On the other hand, the output port 26 is connected to the switching valve IO and the motor 45 via respective drive circuits 30 and 31, respectively.

FIG. 2 shows a longitudinal sectional view of the engine shown in FIG. 1. Referring to FIG. 2, 60 is a cylinder block, 61 is a cylinder head, 62 is a piston, 63 is a substantially cylindrical recess formed on the top surface of the piston 62, and 64 is a space between the top surface of the piston 62 and the inner wall surface of the cylinder head 61. The cylinder chambers formed in the figure are shown respectively. The ignition plug 65 is attached to a substantially central portion of the cylinder head 61 facing the cylinder chamber 64. Although not shown in the drawings, an intake boat and an exhaust port are formed in the cylinder head 61, and an intake valve and an exhaust valve are arranged at the openings of these intake ports and exhaust ports into the cylinder chamber 64, respectively. The fuel injection valve 66 is a swirl type fuel injection valve, and injects fuel in the form of a spray with a large spread angle and a weak penetration force. The fuel injection valve 66 is arranged at the top of the cylinder chamber 64 so as to face obliquely downward, and is arranged to inject fuel toward the vicinity of the ignition plug 65 . Further, the fuel injection direction and fuel injection timing of the fuel injection valve 66 are determined so that the injected fuel is directed toward the recess 63 formed at the top of the piston 62.

FIG. 3 shows control patterns for compression stroke injection and intake stroke injection in this embodiment. Referring to FIG. 3, the horizontal axis represents the engine load, and in FIG. 3, the load is the fuel injection amount Q, and the vertical axis is the fuel injection amount Q. From low load to fuel injection amount Q3, fuel is injected only in the compression stroke. Compression stroke fuel injection iQ. is gradually increased up to QS. Fuel injection amount Q, smell, compression stroke fuel injection iQ. is rapidly decreased to QD, and the intake stroke fuel injection amount Q1 is rapidly increased to Q. QS is the fuel injection amount near medium load, and Q
, and Q, is expressed by the following equation.

Q5=Qo+Q,.

Here, QD is the minimum compression stroke fuel injection amount that can form an air-fuel mixture that can be ignited by the spark plug 65, and QP is the minimum fuel injection amount in the compression stroke that can form a mixture that can be ignited by the spark plug 65. This is the minimum intake stroke fuel injection amount at which the fire ignited by the spark plug 65 can propagate.

In a load region where the fuel injection amount is larger than Q5, the required fuel injection amount Ω is divided into the compression stroke and the intake stroke, and the compression stroke fuel injection amount QD is constant regardless of the load, and the intake stroke fuel injection amount QP is Let it increase as the load increases.

In a load region lower than the medium load vicinity Q5, as shown in FIG.
Fuel is injected toward the recess 63 on the top surface. This injected fuel has a weak penetrating force, and since the pressure inside the cylinder chamber 64 is high and the air flow is weak, the injected fuel is unevenly distributed in the region K near the ignition plug 65. The fuel distribution within this region is non-uniform and changes from a rich mixture layer to an air layer, so within this region there is a combustible mixture layer near the stoichiometric air-fuel ratio where combustion is most likely to occur. Therefore, the combustible mixture layer near the ignition plug 65 is easily ignited, and this ignition fire propagates throughout the heterogeneous mixture layer to complete combustion. In this way, in the low load region lower than medium load, the spark plug 65 is activated in the latter half of the compression stroke.
Fuel is injected near the spark plug 65, thereby forming a combustible mixture layer near the spark plug 65, thus achieving good ignition and combustion.

On the other hand, in the load region higher than Q5 near medium load, the fourth
As shown in the figure, intake stroke injection is performed at the beginning of the intake stroke (FIG. 4(a)), and the fuel injection valve 66 sends the ignitability 6
5 and the recess 63 on the top surface of the piston 62. This injected fuel is a spray-like fuel with a large spread angle and a weak penetration force, and a part of the injected fuel floats in the cylinder chamber 64 and the other part collides with the recess 63. These injected fuels are caused by turbulence R in the cylinder chamber 64 caused by the intake air flow flowing into the cylinder chamber 64 from the intake port.
is diffused into the cylinder chamber 64, and a premixture P is formed between the intake stroke and the compression stroke (see Fig. 4(b)).
)). The air-fuel ratio of this premixture P is such that an ignition fire can propagate. In the state shown in Figure 4(b), the central axis of the injected fuel is directed toward the cylinder wall, so if the penetration force of the injected fuel is strong, there is a risk that part of the spray may directly adhere to the cylinder wall. There is. In this embodiment, there is no particular problem because the injection is performed with a relatively weak penetration force, but in this embodiment, by making this period a non-injection period, the effect of preventing fuel from adhering to the fuel cylinder wall surface is enhanced. Subsequently, compression stroke injection is performed in the latter half of the compression stroke (FIG. 4(C)), and fuel is injected from the fuel injection valve 66 toward the vicinity of the spark plug 65 and the recess 63 on the top surface of the piston 62. This injected fuel is originally directed toward the ignition plug 65 and has a weak penetrating force, and the pressure inside the cylinder chamber 64 is high, so the injected fuel is unevenly distributed in the area K near the ignition plug 65. The fuel distribution within this region is also non-uniform and changes from a rich mixture layer to an air layer, so within this region there is a combustible mixture layer near the stoichiometric air-fuel ratio where combustion is most likely to occur.

Therefore, when the flammable mixture layer near the spark plug 65 is ignited,
As combustion progresses centering around the heterogeneous mixture region K, Figure 4 (
d)). During this combustion process, the fire propagates from the vicinity of the combustion gas B, which has expanded in volume, to the premixture P, and combustion is completed.

In this manner, in medium load and high load regions, fuel is injected at the beginning of the intake stroke to form a mixture for fire propagation throughout the cylinder chamber 64, and fuel is injected at the latter half of the compression stroke to form a mixture for fire propagation throughout the cylinder chamber 64. Spark plug 6
A relatively rich mixture is formed in the vicinity of 5 to form a mixture for ignition and fire nucleation. In this way, good ignition and combustion with high air utilization efficiency can be obtained.

Note that the fuel injection amount is calculated based on a map of the accelerator opening and the engine speed, and the throttle valve opening is calculated based on the fuel injection amount and the engine speed.

By the way, the catalyst 5 does not function sufficiently as a catalyst when the temperature is low, and cannot form crystals that remove harmful components in exhaust gas unless the temperature is 300° C. or higher, for example.

On the other hand, in an engine that performs stratified combustion like the engine of this embodiment, the exhaust gas temperature is low because the amount of intake air is large compared to the amount of fuel supplied into the cylinder.

Therefore, it takes a long time for the temperature of the catalyst 5 to rise, causing the problem that harmful components in the exhaust gas cannot be removed during this time.

Therefore, in the first embodiment, when the catalyst temperature is low and the air-fuel ratio is above a predetermined value, the exhaust control valve 7
The opening degree of the opening is reduced. The opening degree at this time is set to be an intermediate opening degree that does not interfere with running at idle and under low/medium load conditions. When the opening degree of the exhaust control valve 7 is reduced and the exhaust pipe 3 is throttled, the flow path resistance increases, which increases the exhaust pressure, reduces the amount of air supplied to the cylinder, and as a result, the exhaust gas temperature rises. do. As a result, the temperature of the catalyst 5 can be increased in a short time, and the amount of harmful components discharged can be reduced.

FIG. 5 shows a routine for controlling the exhaust control valve 7. This routine is executed by interrupts at regular intervals. First, in step 70, the catalyst temperature T is 300°C.
It is determined whether or not the value is less than or equal to the value. If T>300° C., the catalyst can sufficiently perform its catalytic action, so the routine proceeds to step 71, where the exhaust control valve 7 is fully opened, and this routine ends. On the other hand, if the temperature is 16,300° C., the process proceeds to step 72, where it is determined whether the air-fuel ratio is, for example, 17 or higher. If the air-fuel ratio is smaller than 17, the process proceeds to step 71, where the exhaust control valve 7 is fully opened. If the air-fuel ratio is less than 17, a large amount of air is required for combustion, and if the exhaust control valve 7 is closed and the opening degree is reduced, there is a risk that the air amount will be insufficient and the output will decrease. In this case, the exhaust control valve 7 is fully opened. On the other hand, if the air-fuel ratio is 17 or more, step 73
Then, the exhaust control valve 7 is closed. In this case, the closed valve is not a fully open state, but an intermediate opening. In operating conditions where the air-fuel ratio is 17 or more, combustion occurs even though there is sufficient air to begin with, so the opening degree of the exhaust control valve 7 is reduced to reduce the amount of air supplied into the cylinder. However, it will not interfere with combustion.

FIG. 6 shows a routine for controlling the exhaust control valve 7 in a second embodiment. This routine is executed by interrupts at regular intervals. This routine is almost the same as the routine shown in FIG. 5, and the same steps are given the same step numbers and their explanations will be omitted. Referring to FIG. 6, if the catalyst temperature T is 300° C. or less, the process proceeds to step 74, where it is determined whether or not the engine is in idle operation. Whether it is idling or not,
The determination is made based on the detection signal of the idle switch 42 and the detection signal of the crank angle sensor 43. The exhaust control valve 7 is fully open when the engine is not idling, and is closed when the engine is idling.

Note that during idling operation, the exhaust pipe 3 is constricted, so that the amount of exhaust gas remaining in the cylinder increases.

In other words, good combustion can be obtained because the amount of internal EGR (exhaust gas recirculation) increases.

In the above embodiment, the exhaust control valve 7 is used to increase the flow path resistance of the exhaust pipe 3, but the flow path resistance may be increased by other means.

Further, although one fuel injection valve 66 executes intake stroke injection and compression stroke injection, it has two fuel injection valves, and one fuel injection valve executes intake stroke injection while the other fuel injection valve 66 executes intake stroke injection and compression stroke injection. Compression stroke injection may be performed by an injection valve.

〔Effect of the invention〕

When the temperature of the catalyst is lower than a predetermined temperature, the flow resistance of the exhaust passage is increased and the exhaust gas temperature is increased, so that the time required to raise the temperature of the catalyst is shortened. As a result, the amount of harmful components discharged can be reduced.

[Brief explanation of drawings]

Figure 1 is an overall view of the internal combustion engine, Figure 2 is a longitudinal cross-sectional view of the engine,
Fig. 3 is a diagram showing an example of control patterns for compression stroke injection and intake stroke injection, Fig. 4 is an explanatory diagram showing the state of fuel injection, and Fig. 5 is a diagram showing an example of control patterns for compression stroke injection and intake stroke injection. Flowchart of the Embodiment, FIG. 6 is a flowchart 1 of the second embodiment for controlling the exhaust control valve. 3... Exhaust pipe, 5... Catalyst, 7... Exhaust control valve, 40... Temperature sensor.

Claims (1)

[Claims] In an internal combustion engine that includes a catalyst in an exhaust passage and is capable of stratified combustion, the exhaust passage downstream of the catalyst is provided with resistance changing means for changing the flow resistance of the exhaust passage, and the temperature of the catalyst is lower than a predetermined temperature. When the resistance is low, the flow resistance of the exhaust passage is increased by the resistance changing means.