Two-cycle combustion engine

1. A two-cycle combustion engine, which comprises:

a cylinder block having a cylinder bore defined therein and accommodating therein a reciprocating piston, said piston cooperating with the cylinder bore to define a combustion chamber;

a crankcase having a crank chamber defined therein and accommodating therein a crankshaft of the engine, said cylinder block being fixedly mounted on the crankcase with the cylinder bore communicated with the crank chamber;

said crankshaft being rotatably supported by the crankcase by means of a bearing; and

a scavenging path having a plurality of pairs of scavenging passages defined in part within the cylinder block and in part within the crankcase for supplying an air-fuel mixture from the crank chamber into the combustion chamber, each pair having two scavenging passages confronting to each other, at least one of the scavenging passages having a lower end portion extended to a position where it is held in face-to-face relation with an outer end face of the bearing, such that the air-fuel mixture within the crank chamber is introduced into such scavenging passages mainly through the bearing, thereby to mix and atomize the air-fuel mixture by rotation of the bearing.

2. The two-cycle combustion engine as claimed in claim 1 , further comprising an intake port for introducing the air-fuel mixture into the crank chamber and an exhaust port for discharging exhaust gases from the combustion chamber wherein the scavenging path comprises a pair of first scavenge passages defined adjacent the exhaust port and a pair of second scavenge passages defined adjacent the intake port, each of the first and second scavenge passages having a lower end portion extended to a position, where it is held in face-to-face relation with the outer end face of the bearing for the crankshaft, and communicated with the crank chamber through the bearing.

3. The two-cycle combustion engine as claimed in claim 2 , wherein each of the first and second scavenge passages has a scavenge port; wherein the first scavenge passage has the lower end portion extended to the portion where it is held in face-to-face relation with the outer end face of the bearing for the crankshaft, and-wherein an uppermost edge of the scavenge port of each of the first and second scavenge passages is positioned at a level lower than that of the exhaust port and the uppermost edge of the scavenge port of the first scavenge passage is positioned at a level somewhat higher than that of the scavenge port of the second scavenge passage.

4. The two-cycle combustion engine as claimed in claim 2 , further comprising an introducing window defined in a portion of the second scavenge passage above the bearing so as to open towards the crank chamber.

5. The two-cycle combustion engine as claimed in claim 4 , wherein the introducing window has an opening area smaller than a cross-sectional surface area of the second scavenge passage.

6. The two-cycle combustion engine as claimed in claim 2 , further comprising a connecting hole defined in the crankshaft for communicating the crank chamber with the lower end portion of the scavenging path.

7. The two-cycle combustion engine as claimed in claim 1 wherein the bearing is a rotary bearing that both restricts the flow path and mixes the air-fuel mixture with oil in a rotating action.

8. The two-cycle combustion engine as claimed in claim 1 , further comprising a connecting hole defined in the crankshaft for communicating the crank chamber to the lower end portion of the scavenging path.

9. The two-cycle combustion engine as claimed in claim 8 , wherein an outlet of the connecting hole opens in a direction counter to a direction towards a scavenge port of the scavenging path during a scavenging stroke in which a piston descends.

10. A two-cycle combustion engine, which comprises:

a cylinder block having a cylinder bore defined therein and accommodating therein a reciprocating piston, said piston cooperating with the cylinder bore to define a combustion chamber;

a crankcase having a crank chamber defined therein and accommodating therein a crankshaft of the engine, said cylinder block being fixedly mounted on the crankcase with the cylinder bore communicated with the crank chamber;

said crankshaft being rotatably supported by the crankcase by means of a rotary bearing unit; and

a scavenging path defined in part within the cylinder block and in part within the crankcase for supplying an air-fuel mixture from the crank chamber into the combustion chamber, said scavenging path having a lower end portion extended to a position where it is in fluid connection with an outer end face of the bearing, such that the air-fuel mixture within the crank chamber is only introduced into the scavenging path through the rotary bearing unit that mixes the air-fuel mixture with oil in a rotating action wherein a suppression of a blow-off of the air-fuel mixture is provided.

11. The two-cycle combustion engine as claimed in claim 10 further comprising an intake port for introducing the air-fuel mixture into the crank chamber and an exhaust port for discharging exhaust gases from the combustion chamber wherein the scavenging path comprises a pair of first scavenge passages defined adjacent the exhaust port and a pair of second scavenge passages defined adjacent the intake port, each of the first and second scavenge passages having a lower end portion extended to a position, where it is held in face-to-face relation with the outer end face of the boring for the crankshaft, and communicated with the crank chamber through the bearing, wherein an uppermost edge of a scavenging port of each of the first and second scavenge passages is positioned at a lower level than that of an exhaust port communicating with the combustion chamber and the uppermost edge of the scavenge port of the first scavenge passage is positioned at a level higher than that of the scavenge port of the second scavenge passage.