JPH02264111A - Two-cycle internal combustion engine - Google Patents

Abstract

PURPOSE:To enable the exhaust gas having an air-fuel ratio nearly equal to the inside the cylinder to flow into a first exhaust passage by making the flow passage resistance of the first exhaust passage branched in the vicinity of an exhaust port greater than that of a second exhaust passage. CONSTITUTION:Exhaust branch pipes 45 to 48 are branched into first exhaust pipes 45b to 48b and second exhaust pipes 45c to 48c at the branch parts 45a to 48a in the vicinity of exhaust ports 33 to 36. And the first exhaust pipes 45b to 48b are formed so as to extend in the streamline direction of exhaust gas at the branch parts 45a to 48a, and also the second exhaust pipes 45c to 48c are formed so as to extend in the direction intersecting the streamline of exhaust gas at the branch parts 45a to 48a. And the flow passage resistance of the first exhaust pipes 45b to 48b is made greater than that of the second exhaust pipes 45c to 48c. Accordingly, during the blowdown period, since the flow velocity of exhaust gas is high, burned gas including little fresh air flows in the first exhaust pipes 45b to 48b, so that the exhaust gas having an air-fuel ratio nearly equal to that of the mixture inside the cylinder can be allowed to flow.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a two-stroke internal combustion engine.

[Conventional technology]

Japanese Utility Model Application Publication No. 62-57733 discloses a two-stroke internal combustion engine in which an air intake valve and an exhaust valve are provided in the upper part of the combustion chamber of the two-stroke internal combustion engine, and air intake and exhaust are carried out in a valve system. Issue] In a two-stroke internal combustion engine, the intake port and exhaust port
There is a period when both of the two are open, and this causes a phenomenon in which fresh air supplied into the combustion chamber blows through into the exhaust port. Therefore, in the exhaust passage of a two-stroke internal combustion engine, in addition to the burnt gas from the combustion of the air-fuel mixture in the combustion chamber, fresh air flows through the atrium, and only burnt gas without fresh air flows through the exhaust passage. can't get it. This causes, for example, the following inconveniences. In other words, the burnt gas flowing through the exhaust passage is made lean by fresh air from the blow-through, so even if an 02 sensor is installed in the exhaust passage to detect the air-fuel ratio of the exhaust gas flowing through the exhaust passage, it will not detect the air-fuel ratio in the cylinder. Can not do it. Further, even if a three-way catalyst or a reduction catalyst is provided in the exhaust passage, NOx cannot be purified because the exhaust is made lean by fresh air and there is no reducing atmosphere. If we attempt to purify NOx using a three-way catalyst or a reduction catalyst by making the exhaust gas at the stoichiometric air-fuel ratio or slightly richer than the stoichiometric air-fuel ratio,
It is necessary to make the air-fuel ratio in the cylinder significantly richer, resulting in a significant deterioration in fuel efficiency.

[Means to solve the problem]

In order to solve the above-mentioned problems, according to the present invention, the engine exhaust passage is branched into a first exhaust passage and a second exhaust passage at a branching part near the exhaust port, and the first exhaust passage is connected to the branching part so that the exhaust gas flows. The second exhaust passage is formed to extend in the linear direction, and the second exhaust passage is formed to extend in a direction intersecting the streamline of the exhaust at the branch part, so that the flow resistance of the first exhaust passage is greater than the flow resistance of the second exhaust passage. I'm trying to get bigger.

[For production]

During the blow-down period, the flow rate of the exhaust gas flowing into the exhaust passage is high, so most of the exhaust gas flows into the first exhaust passage formed in the streamline direction of the exhaust gas.

The exhaust gas at this time is all burnt scum. On the other hand, during the scavenging period, the flow rate of the exhaust gas flowing into the exhaust passage is slow, so that most of the exhaust gas flows into the second exhaust passage where the flow resistance is low. Most of the exhaust gas at this time is fresh air.

Thus, burnt gas with little fresh air mixed in flows through the first exhaust passage, and exhaust gas, which is mostly fresh air, flows through the second exhaust passage.

〔Example〕

FIG. 1 shows a four-cylinder, two-stroke internal combustion engine according to a first embodiment. Referring to FIG. 1, ] to 4 are cylinders 1 to 4, 5 to 8 are exhaust valves, 13 to 16 are intake valves, 21 to 24 are intake ports, and 29 to 32 are cylinders 1 to 4, respectively. 33 to 36 are exhaust ports, and 41 to 44 are spark plugs, respectively. Exhaust branch pipe 4
5 to 48 communicate with each cylinder 1 to 4 via exhaust bows 1-33 to 36 and exhaust valves 5 to 8, respectively. Each of the exhaust branch pipes 45 to 48 has branch portions 45a, 46a, 47a and 4 near each exhaust bow 1-33 to 36.
8a, the first exhaust pipes 45b, 46b, 47, respectively.
b, 48b and second exhaust pipes 45c, 46c,
It is branched into 47c and 48c, and a confluence part 45
d, 46d, 47d, and 48d. Fluid diodes 60 to 63 and small-capacity three-way catalysts 49 to 52 are disposed in the middle of each first exhaust pipe 45b to 48b, respectively, and each first exhaust pipe of the first cylinder 1 and the fourth cylinder 4 02 sensors 53 and 54 are disposed downstream of the three-way catalysts 49 and 52 in the three-way catalysts 45b and 48b, respectively. The exhaust branch pipe 45 and the exhaust branch pipe 46 are merged and connected to a first exhaust pipe 55. First exhaust pipe 5
An oxidation catalyst 57 is disposed in the middle of 5. Similarly, the exhaust branch pipe 47 and the exhaust branch pipe 46 are merged and connected to a second exhaust pipe 56, and an oxidation catalyst 58 is disposed in the middle of the second exhaust pipe 56. Electronic control unit 1~ (ECU)
70 is connected to 02 sensors 53 and 54. Also E
CU 70 is connected to air blast valves 29-32.

Since each cylinder 1 to 4 has a similar configuration, the first cylinder 1 will be explained with reference to FIGS. 2 to 4. Referring to FIGS. 2 to 4, 7] is a cylinder block, 7
2 is a piston that reciprocates within the cylinder block 71;
3 is the cylinder head fixed on the cylinder block 71, 74 is the top surface of the piston 2 and the inner wall surface 7 of the cylinder head.
A combustion chamber formed between 38 and 41 indicates an ignition plug, respectively.

A groove 75 is formed on the inner wall surface 73a of the cylinder head 73, so that the cylinder head inner wall surface 73a forms the bottom wall surface of the groove 75.
and a cylinder head inner wall surface portion 73c that is raised toward the combustion chamber 74 with respect to this cylinder head inner wall surface portion 73b.
It will be composed of A pair of air supply valves 13 are arranged on the cylinder head inner wall surface portion 73b, and a single exhaust valve 5 is arranged on the cylinder head inner wall surface portion 73c. The inner wall portions 73b and 73c of each cylinder head are substantially perpendicular and are connected to each other via a circumferential wall 78 of the groove 75, and a pair of air supply valves 13 are disposed on one side of the circumferential wall 78, and on the other side. An exhaust valve 5 is arranged.

This peripheral wall 78 includes a mask wall 78a that is arranged very close to the peripheral edge of the air supply valve 13 and extends in an arc shape along the peripheral edge of the air supply valve 13, and a partial mask wall 78b that is formed between both air supply valves 13. and a fresh air guide wall 78c formed between the peripheral wall surface of the combustion chamber 74 and the air supply valve 1.3. mask wall 7
8c is the air supply valve 13 at the maximum lift position in FIG.
The opening between the peripheral edge of the air intake valve 13 located on the exhaust valve 5 side and the valve seat 79 is connected to the mask wall throughout the opening period of the air intake valve 13. 78
It will be closed by a. On the other hand, partial mask wall 7
8b is a pair of air supply valves 13 from between a pair of mask walls 78a.
It extends towards the middle. The height of this partial mask wall 78b is formed lower than the height of the mask wall 78a.

Therefore, when the lift amount of the air supply valve 13 is small, the opening formed between the air supply valve 13 and its valve seat 79 is the partial mask wall 78b.
When the lift amount of the intake valve 13 increases, the space between the intake valve 13 and its valve seat 79 opens into the combustion chamber 74. In the embodiment shown in FIGS. 2 to 4, the partial mask wall 7
The lower wall surface of the partial mask wall 78b is parallel to the cylinder head inner wall surface portion 73b, but the lower wall surface of this partial mask wall 78b may be arranged at an angle with respect to the cylinder head inner wall surface portion 73b, or the cylinder head inner wall surface portion 73c It can also be formed on an extended surface of. The ignition plug 41 is arranged on the cylinder head inner wall surface portion 73c between the partial mask wall 78b and the exhaust valve 5 so as to be located at the center of the combustion chamber 74. In the cylinder head 73, an air supply port 21 is formed for each air intake valve 13, and exhaust bows 1 to 33 are formed for each exhaust valve 5.

As shown in FIG. 3, each air supply bow 1-21 is connected to an air cleaner (not shown) via an engine-driven mechanical supercharger 75 and throat valves 1-76.

On the other hand, as shown in FIGS. 3 and 4, on the inner wall surface 73b of the cylinder head located between the pair of intake valves 13, so-called Air Plus valves 1 to 2, which inject fuel using compressed air, are arranged. Ru. The air blast valve 29 is connected to a compressed air passage 77, an on-off valve 80 that is driven by an actuator 78 to control opening and closing of the nozzle lower, a compressed air passage 81 branched from the compressed air passage 77, and a valve 80 that is directed into the compressed air passage 81. and a fuel injection valve 82 that injects fuel. The compressed air passage 81 is connected to an engine-driven compressed air supply pump 83, and therefore the compressed air passage 7
7 and 81 are always filled with compressed air. Fuel is injected from the fuel injection valve 82 into the compressed air passage 81, and then the on-off valve 80, that is, the air blast valve 29, is opened. When the on-off valves 80, ie, the two air blast valves, are opened, the injected fuel is injected into the combustion chamber 74 from the seven nozzles together with compressed air.

Referring to FIG. 2, at the branch portion 45a, the first exhaust pipe 45b extends straight in the direction of the exhaust flow line, and the second exhaust pipe 45c intersects the exhaust flow line at almost a right angle. There is. The fluid diode 60 is disposed within the first exhaust pipe 45b between the branch portion 45a and the three-way catalyst 49, and increases the flow resistance of the first exhaust pipe 45. The fluidic diode 60 is a hollow cone 6 as shown in FIG.
5 are arranged in such a manner that their tapered portions 65a face downstream of the exhaust flow line. Therefore, the flow path resistance of the fluid diode 60 in the direction opposite to the exhaust streamline is greater than the flow path resistance in the direction of the exhaust streamline. 1st exhaust pipe 45
Since a fluid diode 60 and a three-way catalyst 49 are disposed in the section b, the flow resistance of the first exhaust pipe 45b from the branching part 45a to the merging part 45d is equal to the flow resistance of the second exhaust pipe 45c. Approximately twice as much.

Figure 6 shows the opening and closing timing of the supply and exhaust valves. Since each cylinder 1 to 4 operates in the same way, the first cylinder 1 will be explained.

Referring to FIGS. 1, 2, and 6, the exhaust valve 5 is opened at a crank angle EO. At this time, since the pressure within the combustion chamber 74 is high, the burned gas within the combustion chamber 74 is rapidly discharged into the exhaust port 33. Therefore, the flow velocity of the exhaust gas flowing into the exhaust branch pipe 45 is high, and most of the exhaust gas flows into the first pipe extending in the streamline direction of the exhaust gas. It flows into the exhaust branch pipe 45b. On the other hand, since the second exhaust pipe 45c extends substantially perpendicular to the streamline of the exhaust gas, almost no exhaust gas flows into the second exhaust pipe 45c. During the blowdown period until the air supply valve 13 opens at IO, burnt debris flows into the first exhaust pipe 45b. Next, when the intake valve 13 is opened at the crank angle ■○, fresh air flows into the combustion chamber 74 from the intake port 21 and scavenging is started.
Since the mask wall 78a is provided for the opening 3, fresh air flows downward along the inner wall surface of the cylinder below the air supply valve 13. Therefore, as shown by arrow S in FIG. 2, the burnt gas in the combustion chamber 74 is gradually pushed away by fresh air and discharged into the exhaust port 11, and thus a strong loop scavenging air is created in the combustion chamber 74. As a result, fresh air does not blow through to the exhaust ports 33 and 37 in the initial stage of scavenging, and only the burnt gas is exhausted.

Since the flow velocity of the exhaust gas flowing into the exhaust branch pipe 45 at the beginning of the scavenging stroke is relatively high, the first exhaust pipe 45b is still
Most of the exhaust gas flows into the tank. At this time, the exhaust gas does not contain fresh air. When the scavenging stroke is started and exhaust gas containing a large amount of fresh air is discharged into the exhaust port 33 by loop scavenging, the pressure within the combustion chamber 74 has decreased to approximately atmospheric pressure. For this reason, the flow velocity of the exhaust gas flowing into the exhaust pipe 45 is considerably lower than that during blowdown, and therefore most of the exhaust gas flows into the second exhaust pipe 45c, which has low flow resistance. Thus, almost no fresh air flows into the first exhaust pipe 45b from the beginning of scavenging until the exhaust valve 5 closes at EC. On the other hand, the exhaust gas flowing through the second exhaust pipe 45c contains a large amount of fresh air.

In this way, the exhaust gas flowing through the first exhaust pipe 45b contains almost no fresh air, and therefore only burned gas having an air-fuel ratio approximately equal to the air-fuel ratio of the air-fuel mixture in the combustion chamber 74 flows. Become. Therefore, by providing the 02 sensor 53 in the first exhaust pipe 45b, the air-fuel ratio of the air-fuel mixture in the combustion chamber 74 can be detected with high accuracy. By controlling the fuel injection amount from the two air blast valves based on the detection signal of the 02 sensor 53, the air-fuel ratio of the air-fuel mixture formed in the combustion chamber 74 can be controlled to the stoichiometric air-fuel ratio. As a result, the exhaust gas flowing inside the first exhaust pipe 45b can be brought to the stoichiometric air-fuel ratio, reducing NOx and IC in the exhaust gas.
and CO can be purified by four three-way catalysts.

The exhaust gas flowing through the second exhaust pipe 45c is the first exhaust pipe 45b.
It flows into the first exhaust pipe 55 and the oxidation catalyst 57. At this time, the second exhaust pipe 4
A small amount of HC and COl contained in the exhaust gas flowing through 5c
and unpurified H in the exhaust gas flowing through the first exhaust pipe 45b.
C and co are purified by the oxidation catalyst 57. Note that the exhaust gas flowing through the second exhaust pipe 45c contains a large amount of fresh air, so the exhaust gas flowing through the oxidation catalyst 57 is lean, and therefore the HC and CO in the oxidation catalyst 57 are
can promote purification. Therefore, supply of secondary air becomes unnecessary.

Note that the 02 sensor is connected to the first exhaust pipe 45 of each cylinder 1 to 4.
Although it is preferable to provide the 02 sensor 53 in each of the first exhaust pipes 45b and 48b, in this embodiment, the 02 sensor 53
, 54 are provided, and the air-fuel ratios of the second cylinder 2 and the third cylinder 3 are controlled based on the detection results of the 02 sensors 53 and 54, respectively.

In addition, in the first embodiment, the first exhaust pipes 45b to 48b
4 to 52 three-way catalysts were used as the catalyst installed in the
A reduction catalyst may be used instead of a three-way catalyst. In this case, the air-fuel mixture in the combustion chamber 74 is made slightly richer than the stoichiometric air-fuel ratio, and the burned gas flowing through the first exhaust pipes 45b to 48b is made into a reducing atmosphere, thereby promoting purification of NOx. Further, unlike the three-way catalyst, the reduction catalyst does not require controlling the air-fuel mixture to a predetermined air-fuel ratio, so there is no need to feedback-control the air-fuel ratio using the 02 sensor. Further, in this case, HC and CO that are not purified by the reduction catalyst can be purified by the oxidation catalysts provided in the first and second exhaust pipes 55 and 56.

Further, although fluid diodes are used in this embodiment, the flow path resistance of the first exhaust pipes 45b to 48b may be increased by other means.

In the first embodiment shown in FIG. 1, the first exhaust branch pipe and the second exhaust pipe are merged for each cylinder, but in the second embodiment shown in FIG. Instead of merging the first exhaust pipe and the second exhaust pipe, the first exhaust pipes of all the cylinders are made to join and the second exhaust pipes of all the cylinders are made to join. Referring to FIG. 7, the second exhaust pipe 104
and 105 merge to become the exhaust main pipe 108, and the exhaust main pipe 1
An oxidation catalyst 109 is provided downstream of 08. The second exhaust pipe 107 joins the second exhaust pipe 106, and the second exhaust pipe 107 joins the second exhaust pipe 106.
6 is the exhaust main pipe 1 at the confluence position 110 upstream of the oxidation catalyst 109.
Join on 08. The first exhaust pipes 102 and 103 merge to form an exhaust pipe 111, and this exhaust pipe 111 is communicated with the exhaust main pipe 108 at a merge position 115 between the merge position 110 and the oxidation catalyst 109. Three-way catalyst 1 in exhaust pipe 111
12 is provided, and the exhaust pipe 11 upstream of this three-way catalyst 112
1 is provided with an 02 sensor 113. 1st exhaust pipe 1
．． 00 and 101 merge to form a merge pipe 114, and the merge pipe 114 is communicated with the exhaust pipe 111 upstream of the 02 sensor 113. Also in this embodiment, the air-fuel mixture in the combustion chamber 74 is 0.
Based on the detection signal of the 2 sensor 113, the air-fuel ratio is controlled to be the stoichiometric air-fuel ratio. The burnt gas that has flowed into the first exhaust ports 33 to 36 flows into the exhaust pipe 111, and NOx, HC, and CO in the burnt gas are purified by the three-way catalyst 112. Furthermore, as in the first embodiment, HC and CQ in the exhaust gas are also purified by the oxidation catalyst 109.

According to this embodiment, the number of 02 sensors and three-way catalysts can be reduced. Further, the 0□ sensor 113 can detect the average value of the air-fuel ratios in all cylinders 1 to 4. Furthermore, since the amount of exhaust gas flowing through the 02 sensor 113 and the three-way catalyst 112 increases, activation of the 02 sensor 113 and the three-way catalyst 112 can be promoted.

Note that as in this embodiment, all the first exhaust pipes 100 to 1
03 into one exhaust pipe 111 will affect the blowdown, so the first and second exhaust pipes 100, 1
01 is collected in the first collecting pipe, and 0 is collected in the first collecting pipe.
Alternatively, the third and fourth exhaust pipes 102 and 103 may be assembled into a second collecting pipe, and the second collecting pipe may also be provided with the 02 sensor and the three-way catalyst. .

Furthermore, if the exhaust pipe 111 of this embodiment is opened to the atmosphere without communicating with the exhaust main pipe 108, the first exhaust port 33
NOx, HC, and CO in the burnt gas that has flowed into the oxidation catalyst 109 is purified only by the three-way catalyst 112, and a part of the NOx purified (reduced) by the three-way catalyst 112 is re-purified by the oxidation catalyst 109. It can prevent oxidation and return to NOx.

In addition, in the above embodiment, the air blast valve was used to inject the fuel into the combustion chamber, but a fuel injection valve was placed in the air intake bow 1 and fuel was injected into the air intake port. It's okay.

〔Effect of the invention〕

Almost no fresh air due to blow-through flows into the first exhaust passage, and exhaust gas having an air-fuel ratio approximately equal to the air-fuel ratio of the air-fuel mixture in the cylinder can flow.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of a four-cylinder two-stroke internal combustion engine according to the first embodiment, FIG. 2 is a side cross-sectional view of the two-stroke internal combustion engine taken along the line ■-■ in FIG. 3, and FIG. Figure 2 is a bottom view of the cylinder head, Figure 4 is a side sectional view taken along line IV-IV in Figure 3, Figure 5 is a diagram showing the hollow conical body of the fluid diode, and Figure 6 is the air supply and exhaust. FIG. 7 is a diagram showing the opening/closing timing of valves, and is a configuration diagram of a four-cylinder two-stroke internal combustion engine according to a second embodiment. 33-36...Exhaust port, 45-48...Exhaust branch pipe, 45a-48a...Branch portion, 45b-48b, 100-103...First exhaust pipe, 45c-48c, 104-107-Second exhaust branch pipe.

Claims (1)

[Claims] The engine exhaust passage is branched into a first exhaust passage and a second exhaust passage at a branch part near the exhaust port, and the first exhaust passage is formed at the branch part so as to extend in the streamline direction of exhaust gas, and the second A two-cycle internal combustion engine, wherein an exhaust passage is formed at the branch part to extend in a direction intersecting a streamline of exhaust gas, and the flow resistance of the first exhaust passage is greater than the flow resistance of the second exhaust passage. institution.