Air-intake device of engine for leisure vehicle and engine

1. An air-intake device of an engine for a leisure vehicle, in which at least two air-intake passages are arranged within a cylinder head of the engine, the air-intake device comprising:

an air-intake pipe having a passage through which fresh air is supplied to the at least two air-intake passages arranged within the cylinder head; and

a throttle valve openably mounted within the passage of the air-intake pipe;

wherein the passage of the air-intake pipe has an air-flow cross-section of a non-perfect circle shape in a direction perpendicular to a longitudinal direction of the air-intake pipe, and the non-perfect circle shape is substantially an elongated circle shape having long and short axes or substantially an oval shape having long and short axes;

wherein the throttle valve has a valve disc of a non-perfect circle shape conforming to the shape of the air-flow cross-section of the passage of the air-intake pipe;

wherein an area of the air-flow cross-section of a portion of the air-intake pipe that is located in the vicinity of the air-intake passage of the cylinder head, gradually decreases toward the air-intake passage, and with a first taper angle of an inner wall of the air-intake pipe which is formed when sectioned along the long axis of the air-flow cross-section and with a second a taper angle of the inner wall of the air-intake pipe which is formed when sectioned along the short axis, the first taper angle being configured to be smaller than the second taper angle.

2. The air-intake device according to claim 1 , wherein the inner wall of the air-intake pipe with the first and second taper angles is formed from a downstream end of the air-intake pipe in air flow to the valve disc and the inner wall of the air-intake pipe with a third taper angle is formed from the valve disc to an upstream end of the air-intake pipe so as to increase the area of the air-flow cross section from the valve disc toward the upstream end.

3. An air-intake device of an engine for a leisure vehicle, in which at least two air-intake passages are arranged within a cylinder head of the engine, the air-intake device comprising:

an air-intake pipe having a passage through which fresh air is supplied to the at least two air-intake passages arranged within the cylinder head; and

a throttle valve having a valve disc and a pivot shaft rotatably supported by the air-intake pipe and openably mounted within the passage of the air-intake pipe;

wherein the passage of the air-intake pipe is configured to have an air-flow cross-section of a non-perfect circle shape in a direction perpendicular to a longitudinal direction of the air-intake pipe; and

wherein the valve disc has a non-perfect circle shape conforming to the shape of the air-flow cross-section of the passage of the air-intake pipe, wherein the air-intake pipe within which the throttle valve is mounted is divided into two parts so that a divided surface of the air-intake pipe is located at an axis of the pivot shaft of the throttle valve.

4. An air-intake device according to claim 3 wherein the pivot shaft is formed to extend outward from both ends of the valve disc, the pivot shaft including a pivot portion being rotatably supported by the air-intake pipe via a bearing and a flange portion provided between the valve disc and the pivot portion to contact the bearing.

5. The air-intake device according to claim 3 , wherein the air-intake pipe is divided at a position of the axis of the pivot shaft of the throttle valve in a direction perpendicular to the longitudinal direction of the air-intake pipe to form an upstream portion and a downstream portion in air flow.

6. The air-intake device according to claim 3 , wherein the air-intake pipe is divided at a position of the axis of the pivot shaft of the throttle valve in a longitudinal direction of the air-intake pipe.

7. The air-intake device according to claim 3 , wherein the non-perfect circle shape of the passage of the air-intake pipe is substantially an elongated circle shape having long and short axes or substantially an oval shape having long and short axes; and

wherein the area of the air-flow cross-section of a portion of the air-intake pipe that is located in the vicinity of the air-intake passages of the cylinder head, gradually decreases toward the downstream end with a first taper angle of an inner wall of the air-intake pipe which is formed when sectioned along the long axis of the area of the air-flow cross-section and with a second taper angle of an inner wall of the air-intake pipe which is formed along the short axis, the first taper angle being configured to be smaller than the second taper angle.

8. The air-intake device according to claim 7 , wherein the inner wall of the air-intake pipe with the first and second taper angles is formed from a downstream end of the air-intake pipe in air flow to the valve disc and the inner wall of the air-intake pine with a third taper angle is formed from the valve disc to an upstream end of the air-intake pipe so as to increase the area of the air-flow cross section from the valve disc toward the upstream end.

9. The air-intake device according to claim 4 , wherein the bearing is a ball bearing and wherein a seal member is externally fitted to an outer end portion of the ball bearing.

10. An engine for a leisure vehicle comprising:

an air-intake device in which at least two air-intake passages are arranged within a cylinder head of the engine, including:

an air-intake pipe having a passage through which fresh air is supplied to the at least two air-intake passages arranged within the cylinder head; and

a throttle valve openably mounted within passage of the air-intake pipe;

wherein the passage of the air-intake pipe has an air-flow cross-section of a non-perfect circle shape in a direction perpendicular to a longitudinal direction of the air-intake pipe

wherein the throttle valve has a valve disc of the non-perfect circle shape conforming to the shape of the air-flow cross-section of the passage of the air-intake pipe; and

wherein an area of the air-flow cross section of a portion of the air-intake pipe that is located in the vicinity of the air-intake passage of the cylinder head, gradually decreases toward the air-intake passage with a first taper angle of an inner wall of the air-intake pipe which is formed when sectioned alone the long axis of the air-flow cross-section and with a second taper angle of the inner wall of the air-intake pipe which is formed when sectioned along the short axis, the first taper angle being configured to be smaller than the second taper angle.

11. An engine for a leisure vehicle, comprising:

an air-intake device in which at least two air-intake passages are arranged within a cylinder head of the engine, including:

an air-intake pipe having a passage through which fresh air is supplied to the at least two air-intake passages arranged within the cylinder head; and

a throttle valve having a valve disc and a pivot shaft rotatably supported by the air-intake pipe and openably mounted within the passage of the air-intake pipe;

wherein the passage of the air-intake pipe is configured to have an air-flow cross-section of a non-perfect circle shape in a direction perpendicular to a longitudinal direction of the air-intake pipe; and

wherein the valve disc has a non-perfect circle shape conforming to the shape of the cross-section of the passage of the air-intake pipe and the air-intake pipe within which the throttle valve is mounted is divided into two parts so that a divided surface of the air-intake pipe is located at an axis of the pivot shaft of the throttle valve.