# US 5,699,761 A · Two-stroke internal combustion engine

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- Number: US 5,699,761 A
- Document ID: US5699761A
- Status: Granted
- Kind: A
- Application number: 08/806,451
- Filed: 1997-02-26
- Granted: 1997-12-23
- Earliest claimed: 1996-03-01
- Assignees: Kioritz Corporation
- Inventors: Shiro Yamaguchi; Masayoshi Miyamoto
- Web page: https://patentgrep.com/patent/US5699761A

## CPC

- F02B 33/30: Control of inlet or outlet ports
- F02B 33/04: with simple crankcase pumps, i.e. with the rear face of a non-stepped working piston acting as sole pumping member in co-operation with the crankcase
- F02B 33/28: Component parts, details or accessories of crankcase pumps, not provided for in, or of interest apart from, subgroups F02B33/02 - F02B33/26
- F02B 63/02: for hand-held tools
- F02F 1/002: {Integrally formed cylinders and cylinder heads}
- F02F 1/22: characterised by having ports in cylinder wall for scavenging or charging
- F02B 2075/025: {two}
- F02B: INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL (gas-turbine plants F02C; hot-gas or combustion-product positive-displacement engine plants F02G)
- F02F: CYLINDERS, PISTONS OR CASINGS, FOR COMBUSTION ENGINES; ARRANGEMENTS OF SEALINGS IN COMBUSTION ENGINES

## Abstract

A two-stroke internal combustion engine in a working machine such as a chain saw has been prone to stalling when the stance of the machine was changed from slanting down to slanting up. Such stalling is minimized when lower longitudinal scavenging passage in the cylinder block of the engine have smaller cross section as compared with upper scavenging passage, and when the crank chamber of the engine includes a flow restricting portion for impeding the flow of liquid fuel into the lower scavenging passage when the stance is changed. The engine has a cylinder block (12), a crankcase (20), scavenging passages (27, 27), and a flow restricting portion (40) on an inner peripheral surface (22a) of the crank chamber (22).

## Claims

### Claim 1

A two-stroke internal combustion engine comprising:
a crank chamber (22) formed by a cylinder block (12) and a crankcase (20) attached to the cylinder block;
an air-fuel mixture suction opening (25) in communication with the crank chamber for admitting air-fuel mixture to the crank chamber;
an exhaust port (28) formed on the cylinder block;
upper and lower scavenging passages (27, 27) formed at an interior wall of the cylinder block in a longitudinal direction of the cylinder block and symmetrical with respect to a lateral cross section (F) through the exhaust port, with the lower scavenging passage having lesser cross section as compared with the upper scavenging passage; and
a flow restricting portion (40) disposed on an inner peripheral surface (22a) of the crank chamber for restricting liquid fuel flow from the crank chamber into the lower scavenging passage.

### Claim 2 (depends on 1)

The two-stroke internal combustion engine according to claim 1, wherein the lower scavenging passage is formed less deep than the upper scavenging passage.

### Claim 3 (depends on 1)

The two-stroke internal combustion engine according to claim 1, wherein the flow restricting portion comprises a concave dam portion (40).

### Claim 4 (depends on 3)

The two-stroke internal combustion engine according to claim 3, wherein the concave dam portion comprise:
a flat surface (40a) formed across the crank chamber so as to extend from an inner peripheral surface portion (22a) of the crank chamber toward the lower scavenging passage;
a concave surface (40b) extending from the flat surface; and
an acute contact portion (40c) formed by the concave surface and a channel bottom portion (27a) of the lower scavenging passage.

### Claim 5 (depends on 1)

The two-stroke internal combustion engine according to claim 1, wherein the air-fuel mixture suction opening has an inner surface portion (25a) which is tangential to the inner peripheral surface portion of the crank chamber.