JPS636432Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a piston device for an internal combustion engine.

Conventionally, in order to keep the combustion chamber airtight and prevent combustion gas from leaking, a piston ring is fitted around the outer periphery of the piston, and the piston is reciprocated up and down while the outer periphery of the piston ring is brought into pressure contact with the inner surface of the cylinder.
Incidentally, the frictional resistance caused by the piston rings accounts for a relatively large amount of engine friction, and it is necessary to reduce the frictional resistance caused by the piston rings in order to improve thermal efficiency. Under these circumstances, reducing the width of the piston ring, the tension of the piston ring, etc. can be considered as a means of reducing the frictional resistance caused by the piston ring.
However, although these measures reduce frictional resistance, they are difficult to prevent gas leakage from the combustion chamber, increase blow-by gas, cause deterioration of lubricating oil, increase heat load on the piston, and reduce engine durability and reliability. becomes.

In view of the above-mentioned circumstances, this proposal aims to reduce engine friction without reducing engine durability and reliability. is formed on the upper small-diameter inner peripheral part, and the lower inner peripheral surface is formed on the lower large-diameter inner peripheral part, and the upper part of the upward annular step formed on the outer periphery of the piston is formed on the upper small-diameter part, and the lower part is formed on the lower large-diameter part. The upper small diameter part of the piston is slidably fitted into the upper small diameter inner periphery of the cylinder liner, and the lower large diameter part is slidably fitted into the lower large diameter inner periphery of the cylinder liner, so that the cylinder liner faces downward. An annular pressure chamber having a compression ratio higher than that of the combustion chamber can be freely formed between the annular step part and the lower large-diameter inner peripheral part and the upper small-diameter part and the upward annular step part of the piston, and the bottom dead center of the piston The piston device is provided with a hole in the lower large-diameter inner peripheral portion of the cylinder liner that faces the annular pressure chamber in the vicinity and communicates with the outside air.

To explain the embodiment of the present invention with reference to the drawings, a cylinder liner 3 fitted into a cylinder bore 2 of a cylinder block 1 has an upper inner circumferential surface of a downwardly directed annular step 4 formed approximately in the middle of the axial length. The lower inner circumferential surface of the downwardly directed annular stepped portion 4 is formed as a lower large-diameter inner circumferential portion 6 .

The piston 7, which reciprocates up and down using the cylinder liner 3 as a guide, has an upper small diameter part 9 above an upward annular stepped part 8 formed on the outer periphery, and a lower large diameter part 10 below. A labyrinth seal ring 12 is fitted into the annular groove 11, and a piston combustion chamber 13 is recessed at the top.

The upper small diameter part 9 of the piston 7 is vertically slidable on the upper small diameter inner peripheral part 5 of the cylinder liner 3 via the labyrinth seal ring 12, and the lower large diameter part 1
0 is capable of vertically sliding on the lower large-diameter inner periphery 6 of the cylinder liner 3, and furthermore, even when the piston 7 reaches the top dead center, the upward annular step 8 of the piston 7 is the downward annular step of the cylinder liner 3. 4, and the downward annular stepped portion 4 and the lower large diameter inner peripheral portion 6 of the cylinder liner 3.
An annular pressure chamber 14 can be formed by the upper small diameter portion 9 of the piston 7 and the upwardly directed annular step portion 8.

Further, the lower large-diameter inner peripheral portion 6 of the cylinder liner 3
An annular groove 15 is formed near the bottom of the cylinder head 1, which faces the annular pressure chamber 14 when the piston 7 reaches near the bottom dead center.
It communicates with the air intake passage 17 communicating with the outside air of No. 6 through a passage 18. Further, when the piston 7 is located near the bottom dead center, the annular pressure chamber 14 is in the annular groove 1.
5. The annular pressure chamber can be freely communicated with the intake passage 17 via the passage 18, and the communication between the annular pressure chamber 14 and the intake passage 17 is cut off due to the upward movement of the piston 7, and the annular pressure chamber is formed when the piston 7 reaches the top dead center. The compression ratio of the combustion chamber 14 is set to be higher than the compression ratio of the combustion chamber 19 formed by the piston 7, the cylinder liner 3, and the cylinder head 16. Note that the lower large-diameter inner peripheral portion 6 of the cylinder liner 3 and the lower large-diameter portion 10 of the piston 7 have relatively small thermal expansion due to combustion gas heat. The annular gap 20 formed with the lower large diameter portion 10 is made as small as possible to maintain the annular pressure chamber 14 airtight.

In the figure, 21 is an intake valve, 22 is an exhaust valve, 23 is a piston pin, 24 is a connecting rod, 25 is a crankshaft, and 26 is a crankcase.

Since the device of the present invention is constructed as described above, when the piston 7 rises during the compression stroke, the combustion chamber 1
The compressed air in the annular pressure chamber 14 attempts to flow out into the crankcase 26 through the gap between the cylinder liner 3 and the piston 7, but because the compression ratio of the annular pressure chamber 14 is set higher than the compression ratio of the combustion chamber 19, the air from the combustion chamber 19 is pushed back, preventing it from flowing out into the crankcase 26.

Further, the air introduced from the passage 18 and compressed in the annular pressure chamber 14 is also prevented from flowing out into the crankcase 26, but the lower large diameter portion 10 of the piston 7 is hardly affected by the heat from the combustion gas. An annular gap 20 between the lower large-diameter inner peripheral part 6 of the cylinder liner 3 and the lower large-diameter part 10 of the piston 7 is formed as small as possible, and an intake passage 17 is formed at the bottom of the lower large-diameter inner peripheral part 6. Since an annular groove 15 is formed which communicates with the air, the air flows out from the annular groove 15 into the intake passage 17, and there is almost no leakage. Even if the amount of leakage increases slightly, only air will leak, so the lubricating oil in the crankcase 26 will not deteriorate.

Next, in the explosion stroke, the combustion chamber 1
Although the pressure in the annular pressure chamber 9 becomes higher than that in the annular pressure chamber 14,
This period is short and even if the annular pressure chamber 14
Even if the air does not flow from the annular groove 15 to the crankcase 26 through the annular gap 20, it will flow from the annular groove 15 to the intake passage 17 in the same manner as described above, and the crankcase 2
6 will not leak.

Furthermore, since the intake valve 21 and the exhaust valve 22 are open during the intake stroke and the exhaust stroke, the pressure within the combustion chamber 19 is approximately equal to atmospheric pressure, so there is no problem.

Therefore, there is no need for a piston ring that has a considerable tension as in the past, and that uses this tension to press against the inner circumferential surface of the cylinder liner and slide up and down in close contact to seal the leakage of combustion gas. Even if the labyrinth seal ring 12 performs sealing by a labyrinth-like groove formed on a small outer circumferential surface, sufficient sealing can be achieved.

According to this device, the annular pressure chamber formed by the piston and cylinder liner and the labyrinth seal ring fitted around the upper circumference of the piston can maintain airtightness in the combustion chamber, so the engine can be kept airtight without reducing engine durability and reliability. It has many practical effects, such as reducing friction as much as possible.

[Brief explanation of the drawing]

The drawing is a sectional view of a main part of the embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Cylinder block, 2... Cylinder bore, 3... Cylinder liner, 4... Downward annular step, 5... Upper small diameter inner peripheral part, 6... Lower large diameter inner peripheral part, 7... Piston, 8 ...Upward annular step, 9
... Upper small diameter section, 10 ... Lower large diameter section, 11 ...
Annular groove, 12...Labyrinth seal ring, 13
... Piston combustion chamber section, 14 ... Annular pressure chamber, 1
5... Annular groove, 16... Cylinder head, 17...
...Intake passage, 18...Passage, 19...Combustion chamber, 20
... annular gap, 21 ... intake valve, 22 ... exhaust valve, 23 ... piston pin, 24 ... connecting rod, 25 ... crankshaft, 26 ... crankcase.

Claims (1)

[Scope of utility model registration request] The upper inner circumferential surface of the downward annular step formed on the cylinder liner is formed on the upper small diameter inner circumference, the lower inner circumferential surface is formed on the lower large diameter inner circumference, and the upward annular step is formed on the outer periphery of the piston. The upper part of the cylinder liner is formed with an upper small diameter part and the lower part is formed with a lower large diameter part, the upper small diameter part of the piston is formed in the upper small diameter inner periphery of the cylinder liner, and the lower large diameter part is formed in the lower large diameter inner periphery of the cylinder liner. are slidably fitted into each other, and the compression ratio is larger than that of the combustion chamber between the downward annular step and the lower large-diameter inner periphery of the cylinder liner and the upper small-diameter and upward annular step of the piston. A piston device which can freely form an annular pressure chamber, and further includes a vent provided in a lower large-diameter inner peripheral portion of the cylinder liner that faces the annular pressure chamber and communicates with outside air near the bottom dead center of the piston.