JPH0312645B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a uniflow type two-stroke engine.

(Prior Art) Conventional two-stroke engines generally have one piston in one cylinder, and the piston is connected to the crankshaft via one connecting rod, and the piston connects the intake port and exhaust port on the inner surface of the cylinder. Since the structure controls the opening and closing of the scavenging port, there were the following drawbacks. That is, (1) The opening and closing of the intake, exhaust, and scavenging ports are at TDC,
Because it is symmetrical around bottom dead center BTC,
There is large blow-by and blow-back of unburned gas, low suction efficiency and charging efficiency, and high fuel consumption rate.
Also, the output is low.

(2) The inertia of the reciprocating part is large, causing large vibrations.

(3) Most of the components are cooled using an external cooling method, which not only requires a large cooling capacity, but also causes large cooling losses because a large amount of heat is carried away to the outside air.

(4) Since scavenging is not completed completely (that is, the combustion gas and scavenging gas are mixed), the output is low, and irregular combustion tends to occur at low speeds.

(Object of the invention) The present invention allows the opening/closing of intake/exhaust and scavenging ports to
The aim is to make it asymmetrical with respect to the bottom dead center so that intake and exhaust can be carried out completely, and to use a uniflow type to improve scavenging efficiency and height output.

(Structure of the Invention) The present invention connects a pair of pistons facing each other in a common cylinder with a phase difference to a common crankshaft via connecting rods, and connects an exhaust port and an intake port to the cylinder part on the side of the piston that has an earlier phase. of,
Furthermore, this is a two-stroke engine characterized in that scavenging ports are provided in each of the cylinders on the slower piston side.

(Example) Fig. 1 is a longitudinal sectional front view perpendicular to the crankshaft during the scavenging stroke, and Fig. 2 is a longitudinal sectional side view taken along the - line in Fig. 1 during the explosion stroke. A head 2 is integrally provided, and the lower end is fixed to a crankcase 3.
Inside the common cylinder 1 is a lower piston 4 with a fast phase.
The upper piston 5, which has a slow phase, is slidably fitted therein and faces the combustion chamber 6 between the pistons 4 and 5 concentrically. An exhaust port 7 and an intake port 8 are provided in the portion of the cylinder 1 within the range in which the lower piston 4 moves up and down, the exhaust port 7 is connected to a muffler 9, and the muffler 9 communicates with the atmosphere via an exhaust outlet 10. are doing. The intake port 8 is connected to a carburetor 12 via an insulator 11, and the inlet of the carburetor 12 communicates with the atmosphere via an air cleaner 13. A scavenging port 14 is provided in the cylinder portion within the range in which the upper piston 5 moves up and down.
This scavenging port 14 communicates with a crank chamber 16 in the crankcase 3 via a scavenging passage 15 (FIG. 2), and when the upper piston 5 descends as shown in FIG. It opens toward the piston back side chamber 17 between the cylinder heads 2. The upper surface of the upper piston 5 and the cylinder head 2
Cooling fins 18 to 21 are integrally provided on the lower surface, upper surface, and outer peripheral surface of the common cylinder 1, respectively. 22 is a spark plug.

The upper piston 5 is connected to a crank arm 27 of a crankshaft 26 via a rod 24 and a connecting rod 25 whose upper ends are fixed at the center thereof. 28 is a connecting pin, and 29 is a crank pin. The lower piston 4 is connected to a crank arm 31 via two parallel connecting rods 30 (FIG. 2) that sandwich the rod 24 therebetween. 32 is a recoil starter, 33 is a handle, and 34 is a flywheel.

FIG. 3 is a graph showing the lower piston displacement A, the upper piston displacement B, and the combustion chamber volume displacement C. Third
As is clear from the lower piston displacement curve A and the upper piston displacement curve B in the figure, when the lower piston reaches the top dead center T (the state shown in Figure 2), the upper piston is in a state L1 before the top dead center. That is, the upper piston is lagged behind the lower piston by L1 (approximately 90 degrees), and this is reflected in the fact that the connecting rod 25 in Figure 1 is slightly inclined with respect to the vertical line. . That is, the upper piston 5 in FIG. 2 is in a state before the top dead center. Since the intake port 8 and the exhaust port 7 are opened and closed by the lower piston 4, they are opened and closed symmetrically with respect to the top dead center T and bottom dead center B of the lower piston 4,
On the other hand, since the scavenging port 14 is opened and closed by the upper piston 5, the bottom dead center of the displacement curve B of the upper piston 5
It is symmetrical with respect to B′. Therefore, as is clear from the opening/closing curves of each port added to the combustion chamber volume displacement curve C, the time when the scavenging port 14 closes is later than the time when the exhaust port 7 closes.
Filling efficiency will be improved. FIG. 4 shows the relationship shown in FIG. 3 in relation to the crank angle.

When the crankshaft 26 rotates while the engine is running, the upper and lower pistons 5 and 4 approach each other, and when the volume of the combustion chamber 6 decreases, the air-fuel mixture that was previously supplied to the combustion chamber 6 is compressed and ignited. Stopper 2
2 causes an ignition explosion. During the stroke in which the upper and lower pistons 4 and 5 are separated from each other due to the explosion pressure in the combustion chamber 6, the rotational force acts on the crankshaft 26, and the lower piston descends, causing the air-fuel mixture pre-pressurized in the crank chamber 16 to be mixed with the upper piston 5. The air-fuel mixture pre-pressurized in the piston back chamber 17 flows into the combustion chamber 6 through the scavenging port 14 due to the rise of the piston.
The exhaust gas in the combustion chamber 6 flows from above to below (in one direction) in the direction of the arrow X in FIG.
Fill the inside with fresh air. And between the upper piston 5 and the lower piston 4, the lower piston 4 has a faster phase,
Since the upper piston 5 is configured to have a slower phase, the intake and exhaust ports 8, 7, and the scavenging port 14 are substantially asymmetrical with respect to the combustion chamber volume displacement C (Fig. 3). .

(Effects of the Invention) As explained above, in the present invention, the opposed pistons 5 and 4 having a phase difference are rotated by the same crankshaft 26, and the intake and exhaust ports 8,
7 is opened and closed by a piston with an earlier phase (the lower piston 4 in the embodiment), and the scavenging port 14 is opened and closed by a piston with a later phase (the upper piston 5 in the embodiment), and a piston with a slower phase than the crank chamber 16 is opened and closed. Connecting the piston back chamber 17 formed on the back side of the upper piston 5,
Cooling fins 18 and 19 are disposed in areas of the piston back chamber 17 that are not on the sliding surface, and the upper piston 5 is operated by passing the rod 24 through the lower piston 4 and connecting it to the connecting rod 25. Special advantages arise, such as:

(1) The intake, exhaust, and scavenging ports open and close asymmetrically with respect to volume changes in the combustion chamber 6 and crank chamber 16, improving output and fuel efficiency. In other words, intake and exhaust can be performed completely.

(2) Since the two pistons 4 and 5 having a phase difference operate substantially opposite to each other, the reciprocating inertia is small and vibrations are significantly reduced.

(3) Since the back sides of the two pistons 4 and 5 are cooled by intake air, internal cooling is increased and cooling loss is reduced (charge cooled method).

(4) Since the scavenging air flow flows from the upper scavenging port 14 of the combustion chamber 6 to the lower exhaust port 7 (uniflow), there is less mixing of fresh air and combustion gas.
Stable combustion and improved output can be achieved.

(5) Since the scavenging port 14 is the only port that is opened and closed by the upper piston 5, the scavenging area can be set large, and the only ports that are opened and closed by the lower piston 4 are the intake port 8 and the exhaust port 7. The exhaust area can be enlarged, and air intake, exhaust, and scavenging can be performed completely from this surface.

When the present invention is applied to an alcohol engine that uses alcohol, which has a large latent heat, as fuel, startability is improved due to the internal cooling effect. Therefore, it is effective for practical application of alcohol engines. Further, the present invention can also be embodied as shown in FIGS. 5 and 6. In FIGS. 5 and 6, a hollow rod 24' is used, and this rod 24' communicates the piston back chamber 17 with the crank chamber 16, and has a structure in which the rod 24 is cooled by intake air. It's summery.

[Brief explanation of the drawing]

Fig. 1 is a longitudinal sectional front view perpendicular to the crankshaft of a two-stroke engine to which the present invention is applied, and Fig.
Figure 3 is a graph showing lower piston displacement, combustion chamber volume displacement, and upper piston displacement; Figure 4 is a port opening/closing characteristic diagram showing Figure 3 in a different form; Figure 5; FIG. 6 is a drawing corresponding to FIGS. 1 and 2 to show another embodiment. 4...Lower piston, 5...Upper piston, 7...
Exhaust port, 8...Intake port, 14...Scavenging port, 25, 30...Conrod, 26...Crankshaft.

Claims (1)

[Claims] 1. 1 facing each other within a common cylinder with a phase difference.
The paired pistons are connected to a common crankshaft via connecting rods, and the exhaust port and intake port are provided in the cylinder part of the piston side that has an earlier phase, and the scavenge port is provided in the cylinder part of the piston side that is slower in phase. Features a 2-stroke engine. 2. A two-stroke engine according to claim 1, wherein a cylinder head is provided on the opposite side of the common cylinder from the crankshaft, and a piston back chamber between the cylinder head and the piston facing the cylinder head is connected to the crank chamber. 3. A piston with a slow phase is arranged above and a piston with an early phase is arranged below, and the operation of the upper piston is performed by connecting a concentric rod passing through the lower piston to a connecting rod. 2-stroke engine. 4. The two-stroke engine according to claim 3, wherein the upper piston and cylinder head are provided with fins that protrude into the back chamber.