JPS641649B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a scavenging air control device for a two-stroke internal combustion engine.

In a conventional uniflow scavenging two-stroke internal combustion engine, as shown in FIG. 1, a scavenging hole b provided in a cylinder liner a is opened and closed by a piston c.
The exhaust valve d is opened and closed by an exhaust cam e.

The cylinder pressure P-volume V diagram in this case is shown in Fig. 2. Compression of the cylinder gas starts at crank angle θ ₄ when the exhaust valve d finishes closing, the cylinder pressure P starts to increase, and the compression Near the end of the stroke, fuel is injected into the cylinder, enters the combustion stroke, and after completion of combustion, the engine enters the expansion stroke.

Further, near the end of the expansion stroke, the exhaust valve d opens from the crank angle θ ₁ and high-pressure exhaust begins.During the high-pressure exhaust period up to θ ₂ , the cylinder pressure decreases from P ₁ to below the scavenging pressure P ₂ .

Furthermore, during the scavenging period from θ ₂ to θ ₃ when the scavenging hole b opens, fresh air is supplied into the cylinder from the scavenging hole b, and the combustion gas (exhaust gas) of the previous cycle is simultaneously discharged from the exhaust valve d.

At this time, the opening area of the scavenging hole b and the exhaust valve d changes as shown by the solid line in FIG.

That is, the exhaust valve d starts opening at θ ₁ and finishes closing at θ ₄ , and the timing of opening and closing is determined by the shape of the exhaust cam e as described above, and therefore, by changing the cam shape, can be easily changed.

Also, the scavenging hole b opens at θ ₂ and closes at θ ₃ , but since it is opened and closed by the piston c, θ ₂ and θ ₃ are the height h from the piston position at bottom dead center to the upper end of the scavenging hole.
Therefore, the crank angle is symmetrical with respect to bottom dead center BDC.

However, one of the effective means of improving the fuel consumption rate of the engine is to lengthen the effective stroke (expansion stroke) of the piston C, but in this way, the exhaust valve opening start point is θ Although it will be delayed from ₁ to θ ₅ , the work received by the piston will increase by ΔPmi shown in the shaded area, and the fuel consumption rate will improve.

By the way, if we take the time when the exhaust valve begins to open as θ ₅ and take the period required for the in-cylinder pressure to drop below the scavenging pressure P _s , that is, the high-pressure exhaust period, then the time when the scavenging hole begins to open becomes θ ₆ , and therefore the scavenging hole b It is necessary to reduce the height h, and furthermore, the closing angle of the scavenging hole becomes earlier than θ ₇ .

As a result, as h becomes smaller, the opening area of the scavenging hole decreases, as shown by the broken line in FIG. 3, and the opening period also decreases, so the opening time area of the exhaust hole becomes insufficient and the scavenging flow rate decreases. A decrease in the excess air ratio in the cylinder causes deterioration in performance such as deterioration of combustion and increase in exhaust temperature. That is, it is not possible to delay the opening of the exhaust valve to _θ5 .

An object of the present invention is to provide a scavenging air control device that makes it possible to improve the fuel efficiency of an engine by ensuring a sufficient scavenging hole opening time area even if the opening of the scavenging hole is delayed. The feature is that in a two-stroke internal combustion engine that has a plurality of scavenging holes in the lower part of the cylinder liner, it is provided corresponding to each of the scavenging holes, and is placed on the outer circumferential side of the scavenging holes at a direction approximately perpendicular to the direction of the scavenging holes. A plurality of closing pieces are swingably supported on shafts formed in the direction to open and close the upper sections of the corresponding scavenging holes, and are connected to each of the closing pieces via a link mechanism to simultaneously swing each of the closing pieces. A drive device such as a hydraulic device is installed in the drive device, and an angle detection signal of the crankshaft of the engine is applied to the drive device to control the drive device, and during the downward stroke of the piston, the height of the scavenging hole is increased by blocking the above-mentioned blocking piece. The present invention further includes a control section for the drive device that lowers the height of the scavenging hole and increases the height of the scavenging hole by opening the closing piece during the upward stroke of the piston.

In this case, even if the start of opening of the exhaust valve is delayed, the high-pressure exhaust period necessary for the cylinder pressure to fall below the scavenging pressure _P5 can be taken long enough to reliably delay the start of scavenging, and the scavenging hole opening can be delayed. A sufficient time area is secured, the scavenging flow rate is increased, and the excess air ratio in the cylinder is improved, so that sufficient combustion can be obtained, and thus it is possible to improve fuel efficiency without causing performance deterioration.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 4 is a sectional view showing the lower part of a cylinder liner provided with a closing piece according to an embodiment of the present invention, FIG. 5 is an explanatory view showing the open state of the closing piece of FIG. 4,
FIG. 6 is an external view showing one embodiment of the hydraulic system according to the present invention, and FIG. 7 is a configuration diagram of the hydraulic system shown in FIG. 6.

In the figure, 1 is a piston, 2 is a piston cylinder, 3 is a cylinder liner, and 4 is a plurality of scavenging holes provided at the bottom of the cylinder liner 3.

Reference numeral 5 denotes a closing piece, which is provided in one-to-one correspondence with each scavenging hole 4 and is rotatable around a shaft 6 provided in a direction substantially perpendicular to the direction of the scavenging hole.

7 is a fork, which moves integrally with the closure piece 5 and has a two-fingered tip.

A drive ring 8 is provided in a ring shape around the outer periphery of the cylinder liner 3, and when it moves up and down, it slides between the fingers of the fork 7 to move the closure piece 5 to the shaft 6.
It is designed to swing around.

9 is a drive arm, which is integrated with the drive ring 8.

10 is a drive link that moves the drive arm 9 up and down.

20 is a hydraulic system, which is composed of the following members.

21 is a hydraulic piston connected to the drive link 10.

A return spring 22 is arranged to push back the hydraulic piston 21.

A hydraulic switching valve 23 switches the hydraulic circuit to the hydraulic piston 21.

24 is an electromagnetic solenoid that drives the hydraulic switching valve 23.

Reference numeral 25 denotes a solenoid control device, which controls the electromagnetic solenoid 24 using a crank angle detection signal sent from a crank angle detector (not shown).

A solenoid control device 25 controls the electromagnetic solenoid 24 based on a crank angle detection signal sent from a crank angle detector (not shown).

With this configuration, the closing piston 5 is swing-controlled via the hydraulic piston 21 and the drive link 10 based on the crank angle detection signal. Note that other drive devices such as a pneumatic device may be used.

The operation in the case of the above configuration will be described.

According to this embodiment, even if the opening of the exhaust valve (not shown) is delayed compared to the conventional engine and high-pressure exhaust is started from the crank angle θ ₅ as shown in FIG. 9, the piston 1 and the piston ring Even after passing through the upper edge of the scavenging hole 4, scavenging does not start because the closing piece 5 is inserted into the scavenging hole 4 as shown in FIG.

Furthermore, when the crank angle reaches θ ₈ after a high-pressure exhaust period equivalent to that of the conventional engine, the electromagnetic solenoid 24 is actuated by the crank angle detection signal as shown in FIG. Switch the hydraulic pressure to move the drive link 10 to
The closure piece 5 rotates around the shaft 6 via the
Since it is extracted from the scavenging hole 4 as shown in Fig. 5,
Scavenging is started.

In addition, by setting the height _h2 of the scavenging hole shown in _FIG . A sufficiently large scavenging time area can be secured.

At an appropriate time after the crank angle θ ₉ of closing the scavenging hole,
As shown in FIG. 8, the crank angle detection signal issues a signal to place the closing piece 5 in the closing position, and the closing piece 5 is inserted into the scavenging hole 4 again to prepare for the next cycle of scavenging air control.

The above case has the following effects.

In the above embodiment, as shown in FIG.
The scavenging hole 4 begins to open at crank angle θ ₈ , which is slower than in conventional engines, but by increasing the scavenging hole height h ₂ compared to the conventional h, the scavenging hole opening area when fully opened at bottom dead center BDC is increased. This is large, and the crank angle at the end of closing is delayed to θ ₉ , so it is possible to take the same amount of scavenging hole opening area time as with conventional engines.

In addition, since the opening area of the scavenging hole is kept approximately the same as in the conventional system, the opening of the scavenging hole can be delayed, so the crank angle at which the exhaust valve starts opening can be delayed, and the effective stroke of the piston is lengthened. As a result, fuel consumption rate is greatly improved.

[Brief explanation of the drawing]

Figure 1 is a front view showing the main parts of a conventional uniflow scavenging two-stroke engine in cross section, and Figure 2 is its P.
-V diagram; FIG. 3 is a diagram showing changes in the opening area of the scavenging holes and exhaust valves of the engine in FIG. 1; FIG. FIG. 5 is an explanatory diagram showing the open state of the closure piece in FIG. 4, FIG. 6 is an explanatory diagram showing an embodiment of the hydraulic system according to the present invention, and FIG. The configuration diagram, FIG. 8 is an explanatory diagram showing the timing of opening and closing of the closure piece, and FIG.
FIG. 6 is a diagram showing changes in the opening area of the scavenging hole and exhaust valve in the example. 3...Cylinder liner, 4...Scavenging hole, 5...
Blockage piece, 6... axis, 7... fork, 8...
Drive ring, 9... Drive arm, 10... Drive link, 20... Hydraulic device, 21... Hydraulic piston, 23... Hydraulic switching valve, 24... Electromagnetic solenoid, 25... Solenoid control device.

Claims (1)

[Claims] 1 In a two-stroke internal combustion engine having a plurality of scavenging holes in the lower part of the cylinder liner, a shaft provided corresponding to each of the scavenging holes and formed on the outer peripheral side of the scavenging holes in a direction substantially perpendicular to the direction of the scavenging holes. a plurality of closing pieces that are swingably supported by the scavenging holes to open and close the upper sections of the corresponding scavenging holes; driving a hydraulic device, etc. that is connected to each of the closing pieces via a link mechanism and swings each of the closing pieces at the same time; A device is provided in the drive device, and an engine crankshaft angle detection signal is applied to control the drive device to lower the height of the scavenging hole by closing the blocking piece during the piston's downward stroke, and to lower the height of the scavenging hole of the piston. A scavenging air control device for a two-stroke internal combustion engine, characterized in that the control unit for the drive device increases the height of the scavenging hole by opening the closing piece during an upward stroke.