JPS6349052B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a two-stroke engine with a crank chamber precompression type suitable for use in motorcycles and other small vehicles. This invention relates to an improvement in a two-stroke engine equipped with an intake valve that opens and closes automatically.

In this type of engine, during the downward stroke of the piston, the intake valve shuts off communication between the intake passage and the inside of the crankcase in conjunction with the crankshaft, preventing the air-fuel mixture introduced into the crankcase from flowing back into the intake passage. Since the fuel is fed under pressure into the combustion chamber, the structure is simple and relatively high output can be obtained. It is known that in order to obtain high output, it is necessary to place the carburetor as close to the crankcase as possible.

However, in engines equipped with this type of intake valve, the pressure inside the crankcase, which fluctuates greatly between positive and negative directions, acts on the fuel nozzle of the carburetor without being buffered, so the fuel flow rate fluctuates constantly during engine operation, causing a drop in the main jet. In other cases, there are many difficulties in setting the fuel supply amount.

The present invention aims to solve the above-mentioned problems, and achieves the purpose with a simple structure in which a relatively small-capacity cavity is connected to the intake passage immediately in front of the intake valve.

Hereinafter, the present invention will be explained with reference to illustrated embodiments. In FIG. 1, a disk-shaped rotary valve is used as an intake valve, and an engine body 1 has a combustion chamber 5 formed by a cylinder 2, a piston 3, and a cylinder head 4. In FIG. 6 is an ignition plug with an ignition electrode facing into the combustion chamber 5.

An exhaust port 7 and scavenging ports 8, 8 are opened in the wall surface of the cylinder 2 forming the combustion chamber 5. The former communicates with the atmosphere through an exhaust passage (not shown), and the latter communicates with the atmosphere via a scavenging passage 9, It communicates with the inside of the crank chamber 11 via 9. Crank chamber 11 is crank case 1
2 and communicates with the atmosphere via an intake passage 13. 14 is the crankshaft and ball bearing 1
It is pivotally supported by the crankcase 12 via 5 and 15, and is connected to the piston 3 via a connecting rod 16. The intake passage 13 includes a cover 17 attached to the outer surface of the crankcase 12 and a carburetor 1.
It is formed in a series through 8. Reference numeral 19 denotes a crankcase cover, in which an air passage leading to the atmosphere is formed in an outer wall 19A, and a reduction gear chamber for transmitting crankshaft output to a transmission is formed in an inner wall 19B. 21 is a piston type throttle valve of the carburetor 18; 21A is a needle valve that cooperates with the fuel nozzle 21B;
1C is the main jet. Reference numeral 22 designates a suction valve having a conventionally known approximately disc-like shape, and is housed in a disc-shaped valve chamber formed by the crankcase 12 and the cover 17, and is connected to the crankshaft 14.
It is engaged with the upper part so as to rotate together with it.
The configuration described above is substantially the same as that of a conventionally known rotary valve type two-stroke engine.

In this invention, the intake passage 13 is located between the throttle valve 21 and the suction valve 22, and in particular, immediately before the suction valve 22, a branch pipe 23 leading to the outside branches off, and the outer end thereof has a relatively small capacity pipe. Vacant room 24 is connected.
25 is a steel pipe forming the passage 23, and 26 is a rubber pipe. The branch pipe 23 needs to be thinner than the intake passage 13, and in particular, the steel pipe 25 has the smallest cross-sectional area. Further, the dimensions of the passage 23 and the cavity 24 are determined so that they cooperate with each other and resonate with pressure fluctuations in a specific period within the intake passage 13. The period is usually at a low frequency below the audible frequency, and the sum of the volumes of both is 1/1/1 of the engine's stroke volume.
It is desirable that it be larger than 3. This volume means that there is a possibility that most of the air-fuel mixture required in a low load range including idling operation can be supplied by the branch pipe 23 and the empty space 24. The dimensions of the steel pipe 25 are preferably such that the length is equal to or larger than the diameter.

FIG. 2 shows another embodiment, in which, instead of the disk-shaped intake valve 22, a piston valve type is used, which is composed of a downstream end 13A of an intake passage 13 that opens in the inner wall of the cylinder 2 and a skirt portion 3A of the piston 3. A suction valve 31 is adopted. The other parts are given the same reference numerals as in the previous embodiment, and the explanation thereof will be replaced.

The two-stroke engine shown in this example is operated as follows. When the air-fuel mixture in the combustion chamber 5 is ignited and combusted by the spark plug 6, the piston 3 is pushed down by the combustion gas pressure. piston 3
When the top surface of the exhaust port 7 is lowered to the exhaust port 7, the exhaust stroke starts and the burnt gas is discharged to the exhaust port. On the other hand, the inside of the crank chamber 11 is shut off from the intake passage 13 by the intake valve 22 or 31, and the air-fuel mixture sucked into the crank chamber 11 is precompressed by the descending piston 3.

When the piston 3 further descends, the scavenging port 8 is opened and the pre-pressurized air-fuel mixture is ejected from the crank chamber 11 into the combustion chamber 5, pushing out the burnt gas inside to the exhaust port, and a so-called scavenging stroke is performed. . When the piston 3 descends to the bottom dead center, it reverses and rises, the intake valve 22 or 31 is opened, and the air-fuel mixture is sucked into the crank chamber 11 from the intake passage 31. Further, the scavenging port 8 and the exhaust port 7 are closed, and a compression stroke is started. When the piston 3 further rises and the compression stroke reaches its final stage, the ignition plug 6 ignites and the predetermined 2
The process ends.

Next, a branch pipe 23 branched from the intake passage 13
And the function of the empty room 24 will be explained. When the intake valve 22 or 31 is closed, the air-fuel mixture flowing from the carburetor 18 and the empty space 24 into the crank chamber 11 is cut off. After that, the air-fuel mixture generated in the carburetor 18 is transferred to the throttle valve 21 due to the intake negative pressure (lower than atmospheric pressure) remaining downstream of the throttle valve 21 and in the empty chamber 24.
The downstream side and the cavity 24 are filled through the opening. That is, when the intake valve 22 or 31 closes, the flowing air-fuel mixture hits the intake valve 22 or 31, but since the branch pipe 23 opens just before this intake valve, the air-fuel mixture flows into the intake passage 13.
It flows into the branch pipe 23 without staying in the pipe. Therefore, even when the intake valve is closed, the air-fuel mixture flows through the throttle valve 21.
Since the air-fuel mixture continues to flow downstream through the intake passage 13, the flow inertia of the air-fuel mixture within the intake passage 13 is maintained. As the stroke of the piston 3 further advances, the suction valve 22
Or, when the valve 31 opens again, the air-fuel mixture rapidly flows into the crank chamber 11 from the carburetor 18 and the empty chamber 24. Therefore, even if the air-fuel mixture flows into and is shut off into the crank chamber 11 by opening and closing the intake valve 22 or 31, the air-fuel mixture generated in the carburetor 18 will flow into the crank chamber 11 and the empty chamber 24. Since the intake air flows into the carburetor 18 alternately, changes in the intake air flow rate in the carburetor 18 are reduced, and the air-fuel ratio of the air-fuel mixture is stabilized. Therefore, in addition to the main jet 21C, selection work for setting a slow jet, slow air jet, etc. (not shown) becomes easy. Furthermore, by appropriately selecting the volume consisting of the branch pipe 23 and the cavity 24, and matching the resonance period to a predetermined engine speed,
The output can be increased in a speed range centered around that speed. From a different perspective, this means that fuel consumption in that operating range can be reduced.

As explained above, the present invention provides a two-stroke engine in which the downstream end of an intake passage equipped with a carburetor is communicated with the crank chamber via an intake valve that opens and closes in conjunction with the crankshaft. Since it is connected to a branch pipe whose outer end was closed immediately before, it eliminates the accumulation of the mixture in the intake passage when the valve is closed and maintains the flow inertia of the mixture, so it opens and closes in conjunction with the crankshaft. There are no excessive fluctuations in intake negative pressure, which are typical of two-stroke engines equipped with intake valves, and the associated drastic increases and decreases in intake air flow rate. Therefore, the air-fuel ratio of the air-fuel mixture generated by the carburetor is stabilized, and the air-fuel ratio can be easily set. As a result, a high-output engine can be achieved.

Incidentally, it goes without saying that the branch pipe is not limited to one having a cavity as in the embodiment.

[Brief explanation of drawings]

The drawings show an example of carrying out the present invention. Fig. 1 is a sectional view of a main part of a two-stroke engine equipped with a rotary valve type intake valve, and Fig. 2 shows another embodiment, in which a piston valve type intake valve is used. 1 is a sectional view of a main part of a two-stroke engine equipped with an intake valve. 11...Crank chamber, 13...Intake passage, 23
...branch pipe, 24...vacant room.

Claims (1)

[Claims] 1 In a two-stroke engine in which the downstream end of the intake passage 13 equipped with the carburetor 18 is connected to the inside of the crank chamber 11 via intake valves 22 and 31 that open and close in conjunction with the rotation of the crankshaft 14, valve 2
An intake system for a two-stroke engine, characterized in that a branch pipe 23 whose outer end is closed is connected to an intake passage 13 immediately before the intake passages 2 and 31.