JPS5851376Y2 - Scavenging device for crank chamber compression type 2-stroke engine - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a scavenging device that is effective in improving the scavenging efficiency of a crank chamber compression type two-stroke engine.

In a crank chamber compression type two-stroke engine that has an exhaust port and a scavenging port on the inner surface of the cylinder, due to its structure, the opening and closing timing of the scavenging port is symmetrical with respect to bottom dead center.

However, since the pressure inside the cylinder and the pressure inside the crankshaft vary widely depending on various operating conditions 1, the appropriate timing for opening the scavenging air is between 20° and 40° after the exhaust opening (so-called exhaust lead); As shown in FIG. 1, the timing varies greatly depending on the rotation speed due to the crank chamber pressure.

For example, when the practical minimum rotation speed N=300 ORPM, the bottom dead center and the subsequent optimal scavenging closing timing 0 are θ1=20°, but when the maximum rotation speed N2=7000, θ2=800.

Therefore, in the conventional scavenging port, the scavenging opening timing is 20' after the exhaust opening.
Since it was set between -40° (Fig. 3), the scavenging closing timing was naturally symmetrical to this (normally 500 to 70° after bottom dead center).
), and in the second half of the scavenging stroke (period a in Figure 3), the original scavenging action of fresh air flowing from the crank chamber into the cylinder is not carried out in the low rotation speed range, and conversely, the backflow from the cylinder to the crank chamber occurs. This phenomenon was observed, resulting in a decrease in scavenging efficiency and a decrease in the air supply ratio, resulting in difficulty in producing low-speed torque and poor fuel efficiency.

As a countermeasure to this problem, it is conceivable to arrange a check valve in the middle of the scavenging passage connecting the scavenging port and the crank chamber to allow the flow from the crank chamber only into the cylinder.

However, in this case, all fresh air passes through the check valve regardless of operating conditions such as rotation speed and load, so the opening area of the check valve must be large, which reduces durability. do.

In addition, the flow rate coefficient becomes small (resistance is large), and performance deterioration due to this is unavoidable.

This invention divides the scavenging port into at least two parts, upper and lower, and places a check valve only in the scavenging passage connecting the upper scavenging port and the crank chamber, making the scavenging timing asymmetric and variable as shown in Figure 3. One embodiment is shown in FIG.

The cylinder 1 in FIG. 2 has an exhaust port 2, an upper scavenging port 3, and a lower scavenging port 4 on its inner surface, and the exhaust 0.2 has an exhaust passage 5.
The upper scavenging port 3 communicates with the crank chamber 8 via an upper scavenging passage 6 and a check valve 7, and the lower scavenging port 4 communicates with the atmosphere via a lower scavenging passage 9. It communicates directly with the crank chamber 8.

The check valve 7 has a characteristic of allowing fresh air to flow only from the crank chamber 8 into the cylinder 1, and is specifically a reed valve.

A piston 10 slidably fitted into the inner surface of the cylinder 1
is connected to a crank arm 14 via a piston pin 11, a connecting rod 12, and a crank pin 13, and performs reciprocating motion up and down by the rotation of the crank arm 14, and cooperates with the exhaust port 2 and the scavenging ports 3 and 4. Form piston pulp.

Note that 15 is an intake passage, 16 is an intake reed valve, 17 is a carburetor, and 18 is a spark plug.

Incidentally, regardless of the suction method using the beam valve method, the scavenging method of the present invention can be implemented even if a piston valve method, rotary valve method, etc. are adopted.

The opening/closing timing of the lower scavenging port 4 controlled by the piston 10 is set to the appropriate scavenging closing timing θ1 (Fig. 1) at the lowest practical engine speed N1, and the opening timing of the upper scavenging port 3 is set to the appropriate scavenging closing timing θ1 (Fig. 1) at the lowest practical engine speed N1. It is set at an appropriate time after the opening of step 2.

As mentioned above, a check valve 7 is inserted between the upper stage scavenging port 3 and the crank chamber 8, which allows air to flow only from the crank chamber 8 to the cylinder 1 side. The structure is such that the scavenging action is performed by the difference in indoor pressure.

When the crank arm 14 rotates in the direction of the arrow from the state shown in FIG. 2, the pressure in the crank chamber 8 is reduced due to the rise of the piston 10, and the air-fuel mixture (fresh air) formed in the carburetor 17 enters the crank chamber 8.

The ascending piston 10 closes the scavenging ports 4, 3 and the exhaust port 2 in that order, compressing the fresh air that had been filled in the cylinder 1 until then, and igniting it and causing an explosion by the spark supplied from the ignition plug 18 at a predetermined timing. and exerts a downward force on the piston 10.

When the piston 10 descends from the top dead center, the exhaust port 2 first opens as shown in Fig. 3, and the high-temperature, high-pressure combustion gas in the cylinder 1 blows down from the exhaust port 2, followed by the conventional scavenging port opening. The upper stage scavenging port 3 opens earlier than the timing, and the lower stage scavenging port 4 opens later than the conventional scavenging port opening timing.

As shown in Fig. 1, the opening timing of the lower scavenging air port 4 is set to an appropriate scavenging closing position θ1 at the lowest practical engine speed N1, and the upper scavenging passage 6 is provided with a check valve 7. Due to the difference between the cylinder internal pressure and the crank chamber pressure, the scavenging closing timing of the upper stage scavenging port 3 becomes the optimum scavenging closing timing θ1 when the lower stage scavenging port 4 is closed when the practical minimum rotation speed N1 is reached.

As the engine speed increases, the relationship between the pressure inside the cylinder and the pressure inside the crankshaft during the scavenging stroke changes, and the scavenging closing timing is delayed from θ1, and even after the lower scavenging port 4 is closed by the rising piston 10, the pressure inside the cylinder 1 changes. While the pressure in the crank chamber 8 is higher, fresh air flows into the cylinder 1 from the upper scavenging port 3.

At the maximum rotational speed N2, the flow of fresh air into the cylinder 1 from the upper scavenging port 3 is stopped at the optimum scavenging closing timing θ2.

Therefore, the scavenging opening period including the bottom and lower scavenging ports of this invention is 8 points and 1 from point A in Figure 3 when the practical minimum rotation speed is N1, and from point A in Figure 3 when the maximum rotation speed is N2. It reaches point C and is variable depending on the rotation speed.

As explained above, Song devised a crank chamber compression type two-stroke engine equipped with an exhaust port 2 and scavenging ports 3, 4 on the inner surface of the cylinder 1. Scavenging ports 3 and 4 are opened, the upper scavenging port 3 communicates with the crank chamber 8 via a check valve 7 that allows flow only from the crank chamber 8 into the cylinder 1, and the lower scavenging port 4 communicates with the crank chamber 8. According to the present invention, the scavenging timing is asymmetric and variable as shown in Fig. 3, and therefore the cylinder changes in response to changes in rotational speed and throttle valve opening. The scavenging action is carried out in response to fluctuations in internal pressure and crank chamber pressure, making it possible to obtain the best scavenging efficiency.

As a result, (1) Improved torque and rotation speed stability in the full throttle low speed range (2) Reduced fuel efficiency (3) Improved stability during partial load and idle link...
・You can expect the following effects.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the optimum scavenging air closing timing with respect to the engine rotation speed, FIG. 2 is a schematic vertical cross-sectional view of an engine to which the present invention is applied, and FIG. 3 is a drawing showing the opening/closing timing of the scavenging air opening. 1...Cylinder 2...Exhaust port, 3
...Upper scavenging port (Dobe scavenging port), 4...
・Lower scavenging port (lower scavenging port), 7...Check valve,
8...Crank chamber, 10...Piston.

Claims (1)

[Scope of utility model registration request] In a crank chamber compression type two-stroke engine equipped with an exhaust port 2 and scavenging ports 3 and 4 on the inner surface of the cylinder 1, the piston 1
0 At least two scavenging ports 3 and 4 are opened vertically and spaced apart in the sliding direction, and the upper scavenging port 3 is connected to the crank chamber through a check valve 7 that allows air to flow only from the crank chamber 8 into the cylinder 1. 8, and the lower scavenging port 4 directly communicates with the crank chamber 8.