JPS641488Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Field of Application] This invention relates to a pressure reducing device for an engine to facilitate starting in cold regions.

[Prior Art] In general, it becomes difficult to start an engine when it becomes supercooled, so conventionally, a pressure reducing device has been provided to release gas in the combustion chamber to the outside only at the time of starting, thereby reducing the pressure, thereby making starting easier. things are being done.

This type of pressure reducing device communicates the combustion chamber and the exhaust passage through a pressure reducing passage, and this pressure reducing passage is equipped with a pressure reducing valve that is made of a bimetal or a bellows filled with mercury and operates in response to the temperature of the cylinder. A device is known in which the pressure reducing passage is opened only when the temperature is low (see Japanese Patent Publication No. 57-060077).

[Problems to be Solved by the Invention] The conventional device described above has the advantage that the pressure is automatically reduced at low temperatures, improving startability.

However, since the pressure reduction passage communicates with the exhaust passage, there is a drawback that during pressure reduction, gas in the combustion chamber passes through the pressure reduction passage and the exhaust passage and is wasted to the outside. In addition, with pressure reducing valves that utilize the deformation of bimetals or the expansion of mercury, the valve moves continuously in proportion to the temperature, so it is not possible to open and close the pressure reducing passage suddenly at a given temperature. In this range, the valve is either slightly open or weakly closed, resulting in unstable operation.

[Means for Solving the Problems] This invention was made to solve the above problems, and includes providing a decompression passage between the combustion chamber and the intake passage, and using a spring body made of a shape memory alloy. The pressure reducing passage is opened and closed by a pressure reducing valve.

In addition to simply using a spring body made of a shape memory alloy, this spring body is also used as a compression spring to apply spring force to the valve body of the pressure reducing valve in the closing direction, while opening the valve body. An opening spring that applies a spring force in the direction is attached to and attached to the spring body, and when the spring body is heated, it stretches against the spring force of the opening spring and restores its original shape. This causes the valve body to close.

Furthermore, at least a portion of the valve case that accommodates the spring body is made to protrude to the outer periphery of the cylinder.

[Function] According to the above configuration, the pressure reduction passage communicates with the intake passage, so that when the pressure is reduced, the gas in the combustion chamber is returned from the intake passage to the combustion chamber and combusted. In addition, the above spring body has the following characteristics as a shape memory alloy:
Since it expands rapidly at a predetermined temperature and firmly maintains its expanded state, the valve body can be quickly closed and firmly maintained in its closed state.

Furthermore, since the spring body made of a shape memory alloy is used as a compression spring and an opening spring is provided opposite to this spring body, the spring body becomes more compressive as the temperature decreases due to the properties of the shape memory alloy. Since the spring force in the compressed state decreases, the lower the temperature, the more the spring force of the opening spring becomes stronger.
Open the decompression passage more widely. Moreover, by appropriately selecting the spring constant of the opening spring,
By changing the balance with the spring body, the degree of opening of the decompression passage can be changed.

In addition, since at least the portion of the valve case that accommodates the spring body protrudes from the outer periphery of the cylinder, the spring body is cooled by outside air, and as a result, when restarting, the cylinder is warmed up. However, the temperature of the spring body drops more quickly than the temperature of the cylinder, loses its tension, and contracts under the force of the opening spring, opening the decompression passage.

[Example] Hereinafter, an example of this invention will be described with reference to the drawings.

In FIG. 1, 11 is a cylinder of a two-stroke engine, a piston 12 is housed inside, and a cylinder head 13 is attached to the upper part.
The cylinder 11 is provided with an intake passage 14, and the air-fuel mixture 15 sucked into the lower part of the piston 12 from this ventilation passage 14 passes through a scavenging passage (not shown) into a combustion chamber 16 above the piston 12. It is starting to explode and burn.

A decompression passage 17 is provided in the cylinder 11 and communicates the combustion chamber 16 with the intake passage 14 . A pressure reducing valve 19 is provided midway through the pressure reducing passage 17, and the pressure reducing passage 17 is opened and closed by its valve body 20. The valve body 20 is housed in a valve case 21, and the valve case 21 is screwed into the cylinder 11. A coil spring (spring body) 23 made of a shape memory alloy is attached to one side of the outer end flange portion 22 of the valve body 20 . This coil spring 23 applies a spring force to the valve body 21 in the closing direction, and is a so-called compression spring that stores spring force through compression and exerts spring force in the direction of extension. A valve body 2 is provided on the other side of the flange portion 22 in a direction that compresses the coil spring 23, that is, in an outward direction 24.
An opening spring 25 is installed to move the pressure reducing passage 17 and open the decompression passage 17. The opening spring 25 is
Made of spring material according to JIS standards. Further, at least the portion (right side) of the valve case 21 that accommodates the spring body 23 protrudes from the outer periphery of the cylinder 11 and is air-cooled.

The shape memory alloy that constitutes the coil spring 23 is
It is made of a TiNi alloy, and when it is heated and reaches a certain temperature, it rapidly expands and returns to its original shape. Below the predetermined temperature, it does not lose its tensile strength, but is compressed by the spring force of the opening spring 25 and maintains the state shown in FIG. 1.

In the above configuration, when starting the engine, if the cylinder 11 is in a cooling state and the temperature is below a predetermined temperature, the coil spring 23 is compressed by the spring force of the opening spring 25, and the tip of the valve body 20 is compressed as described above. The portion 26 is separated from the valve seat 27 and the pressure reduction passage 17 is opened. When the engine is started in this state, a portion of the high-pressure gas in the combustion chamber 16 flows out into the intake passage 14 through the pressure reduction passage 17, so the compression ratio becomes small and the engine starts easily. The gas flowing into the intake passage 14 is mixed with the air-fuel mixture 15 and returned to the combustion chamber 16, so there is no waste.

When the engine starts and the rotational speed increases and the cylinder 11 is heated and reaches a predetermined temperature, the coil spring 23 expands rapidly, pushing the valve body 20 inward 29 as shown in FIG. Move the tip 26
is brought into pressure contact with the valve seat 27 to close the pressure reduction passage 17.
This allows the engine to operate at its normal high compression ratio. At this time, the spring body 23, as a property of the shape memory alloy, expands rapidly at the predetermined temperature and firmly maintains the expanded state.
After quickly closing the valve body 20, the closed state is firmly maintained. Therefore, the operation of the pressure reducing valve 19 is stabilized.

Next, when starting the engine again after stopping the engine, if the engine is still warmed up and the temperature of the cylinder 11 is sufficiently higher than the predetermined value,
Even if the valve case 21 is cooled by the surrounding air and becomes lower temperature than the cylinder 11, the temperature will still be higher than the predetermined temperature, so the valve body 20
Close the decompression passage 17 in the position shown in the figure. Since it is easy to start the engine in such a warmed-up state, there is no need to open the pressure reduction passage 17 to reduce the pressure. By closing the pressure reduction passage 17 as shown in Figure 2, the engine can be started. Gas in the combustion chamber 16 can be prevented from flowing out to the outside without deteriorating startability.

By the way, the predetermined temperature at which the spring body 23 expands and closes the decompression passage 17 cannot be set too high because it is necessary to quickly shift the engine to a normal operating state without depressurization. Therefore, when restarting, if the temperature of the cylinder 11 is sufficiently higher than the predetermined temperature, restarting is easy even if the decompression passage 17 is closed as described above.
When the temperature of the cylinder 11 is slightly higher than the predetermined temperature, there is no sufficient warm-up condition, and as a result, startability deteriorates.

However, at least the portion of the valve case 21 that accommodates the spring body 23 protrudes outward from the outer peripheral surface of the cylinder 11. Therefore,
This portion is cooled by the outside air, and as a result, even if the temperature of the cylinder 11 is above the predetermined temperature, the spring body 23 drops below the predetermined temperature and loses its tension, causing the opening spring 25 to It contracts under pressure from the spring force, opens the decompression passage 17, and improves restartability. Generally, as the temperature of the cylinder 11 decreases, it becomes more difficult to start the engine.
In this invention, as a property of the shape memory alloy constituting the coil spring 23, the spring force in the compressed state decreases as the temperature decreases, so the spring force of the opening spring 25 shown in FIG. More outward than 24
to open the decompression passage 17 more widely. Therefore, as the temperature of the cylinder 11 decreases, the amount of pressure reduction increases and the startability is further improved, so there is an advantage that the startability of the engine is improved even in extremely low temperature ranges. .

Furthermore, since an opening spring 25 is provided alongside the spring body 23, by appropriately selecting the spring constant of the opening spring 25, the balance with the spring body 23 can be changed, and the pressure reducing passage 17 can be Another advantage is that the amount of pressure reduction can be easily adjusted to suit the engine size and application by changing the degree of opening of the engine.

Figure 3 shows another embodiment of this invention.
Instead of a coil spring, the leaf spring 30, which also operates as a compression spring, is constructed of a shape memory alloy, but its operation is the same as in the embodiment shown in FIGS. 1 and 2. Furthermore, in the embodiment shown in FIG. 3, air cooling fins 31 are integrally formed on the outer periphery of the valve case 21 to cool the leaf spring 30 more actively. In this way, for example, if starting is particularly difficult and the starting operation is repeated many times, the cylinder 11
Even if the temperature of the leaf spring 30 rises to a much higher temperature than the predetermined temperature, the leaf spring 30 is effectively cooled and kept below the predetermined temperature, and the decompression passage 17 remains open, making it easy to start. This is advantageous because it maintains the

In each of the above embodiments, if the engine has a water-cooled structure, the entire valve case 21 may be cooled using the cooling water, and the spring bodies 23 and 30 can be cooled more effectively. be done.

[Effects of the invention] As described above, according to this invention, the gas in the combustion chamber is returned to the combustion chamber from the intake passage and burned when the pressure is reduced, and is not wasted to the outside. Additionally, when the cylinder reaches a predetermined temperature, the spring body made of shape memory alloy expands, quickly closing the valve body, and firmly maintaining the closed state, resulting in stable operation of the valve body. . Furthermore, the spring body made of a shape memory alloy opens the decompression passage more widely as the temperature decreases, so starting performance is improved even in extremely low temperature ranges. Furthermore, by appropriately selecting the spring constant of the opening spring, the degree of opening of the pressure reduction passage can be changed, so there is an advantage that the amount of pressure reduction can be easily adjusted in accordance with the size and application of the engine. In addition, since the spring body is cooled by outside air, even if the cylinder temperature is above the predetermined temperature when restarting, the temperature of the spring body quickly decreases to below the cylinder temperature.
Since the expansion force is lost and the decompression passage is opened, restartability is improved.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing an embodiment of this invention.
FIG. 2 is a longitudinal cross-sectional view of the main parts showing the operation of the same embodiment;
FIG. 3 is a longitudinal sectional view showing another embodiment of this invention. 11...Cylinder, 14...Intake passage, 16...
...combustion chamber, 17... pressure reducing passage, 19... pressure reducing valve,
20... Valve body, 21... Valve case, 23, 30...
...Spring body (shape memory alloy), 25... Spring for opening.

Claims (1)

[Scope of utility model registration request] A pressure reducing passage provided in the cylinder and communicating the combustion chamber in the cylinder with the intake passage, a valve body opening and closing this pressure reducing passage, an opening spring applying a spring force to the valve body in the opening direction, and the valve body. It consists of a compression spring made of a shape memory alloy that applies a spring force in the closing direction to the valve body, and when heated, it expands against the spring force of the opening spring and returns to its original shape, thereby closing the valve body. The valve case includes a spring body to be actuated, and a valve case attached to the cylinder to house the valve body, the opening spring, and the spring body, and at least a portion of the valve case housing the spring body protrudes from the outer periphery of the cylinder. A pressure reducing device for the engine.