JPH0721871Y2 - Exhaust system for 2-cycle engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention includes a main exhaust passage and a sub-exhaust passage, and a rotary sub-valve for opening and closing the sub-exhaust passage to the main exhaust passage. Relates to an exhaust system for a two-cycle engine provided with a main valve capable of changing the cross-sectional area of the passage.

(Prior Art) In a conventional exhaust device of this type, there is a main valve having the following structure.

In FIG. 12, a main valve 60 is swingably mounted on the upper wall of the main exhaust passage 2 via a support shaft 64, and a cam pin 61 provided on the main valve 60 is used as a cam of a sub valve for opening and closing the sub exhaust passage. The main valve 60 is engaged with the groove by the cam mechanism simultaneously with the rotation of the sub-valve to change the exhaust cross-sectional area and the exhaust timing of the main exhaust passage 2 (Japanese Patent Laid-Open No. 63-173817). 2 to 4).

In FIG. 13, the rotary type main valve 65 is horizontally installed on the upper wall of the main exhaust passage 2, and the main valve 65 is attached to the lower rack teeth 66a of the drive rod 66 for rotating the sub valve for opening and closing the auxiliary exhaust passage. Of the gear 68 of Japanese Patent Laid-Open No. 64-15
425).

In the structure shown in FIG. 14, an inclined valve hole 69 is formed in the upper wall of the main exhaust passage 2, and the main valve 70 is slidably fitted in the valve hole 69, and rack teeth 71 on the side surface of the main valve 70 are formed. Engages with the pinion 76 of the sub valve 75
63-173817 (Fig. 8).

However, the following phenomena may occur in each of the above structures.

In the swing-type main valve 60 of FIG. 12, the entire main valve 60 is constantly exposed to exhaust gas, and the main valve 60 is installed near the cylinder and its position does not change. It is greatly affected by the heat of explosion. Therefore, a certain amount of backlash is inevitably required between the main valve 60 and the recess 62 that houses the main valve when the main valve is fully opened. That is, when the main valve is fully opened, there is a relatively large clearance d between the recess 62 and the main valve 60.

Existence of such a gap d causes exhaust gas to flow into the gap d when the main valve 60 is housed at a high speed (state of FIG. 12) and to be mutually exchanged with the exhaust gas in the main exhaust passage 2. They interfere with each other and disturb the flow of exhaust gas, resulting in a drop in output.

In the rotary main valve 65 shown in FIG. 13, the main valve 65
The gear 68 is always exposed in the main exhaust passage 2, and a clearance d is formed near the meshing portion with the drive rod 66. Exhaust gas flows into the clearance d, disturbs the flow of exhaust, and outputs Cause a drop.

Further, in the rotary type main valve, since the depth of the notch is limited, the variable stroke of the exhaust timing cannot be made large.

In the case of the sliding type shown in FIG. 14, the pinion 76 of the sub valve 75 arranged on the cylinder side of the drive rod 66 is
It is extended downward to engage with the rack teeth 71 of the main valve 70. Therefore, the meshing portion of the pinion 76 and the rack tooth 71 of the main valve 70 is exposed in the main exhaust passage 2,
Exhaust gas enters the gear meshing part, disturbs the flow of exhaust gas, and causes a reduction in output.

(Object of the Invention) The object of the present invention is to reduce the turbulence of exhaust gas at low and medium speed rotations while improving the output at low and medium speed rotations while maintaining the output at high rotation speeds.

(Technical means for achieving the object) In order to achieve the above object, the present invention forms a main exhaust passage and an auxiliary exhaust passage communicating with the inside of a cylinder, and opens and closes the auxiliary exhaust passage with respect to the main exhaust passage. A rotary sub-valve is provided, a valve hole is formed in the upper wall of the main exhaust passage, which opens in a downward slope toward the cylinder side, and the main valve is slidably fitted in the valve hole to drive both valves. A drive rod for moving in the rod length direction according to the number of revolutions, and a first rack tooth is provided on the cylinder side of the drive rod.
The second rack tooth is formed on the opposite side, the pinion of the sub-valve is meshed with the first rack tooth, the idle gear is meshed with the second rack tooth, the rack tooth is meshed with the side surface of the main valve and meshed with the idle gear. By moving the drive rod when the number of revolutions increases, the main valve opens to increase the cross-sectional area of the main exhaust passage, and at the same time the sub valve opens, and when the main valve opens, the rack teeth of the main valve enter the main exhaust passage. I try not to expose it.

(Embodiment) FIGS. 1 to 10 show a two-cycle engine to which the present invention is applied, and a cylinder 1 is shown in FIG. 4 showing a horizontal sectional view.
A main exhaust passage 2 communicating with the inside of the cylinder 1 and sub-exhaust passages 3 on both sides of the main exhaust passage 2 are formed in the wall 1a of the cylinder 1. One end of the sub-exhaust passage 3 opens into the cylinder 1 and the other end Is connected to the middle portion of the main exhaust passage 2 via a sub valve 6 so as to be openable and closable. Each sub-valve 6 is rotatably supported in the valve support hole 6a of the cylinder wall 1a in a posture parallel to the cylinder center line O1. The sub-valve 6 is installed at a position apart from the cylinder 1 in order to keep the wall thickness of the cylinder wall 1a sufficient.

In the main exhaust passage 2, a pair of main valves 7 for changing the exhaust cross-sectional area of the main exhaust passage 2 are arranged.

In FIG. 5, a drive rod insertion hole 13 is formed in a wall 1a on the exhaust side of the cylinder 1, and a drive rod 12 extending in a direction substantially orthogonal to the cylinder center line O1 is formed in the insertion hole 13 and has a rod length. It is arranged so that it can move in any direction. A base end portion (right end portion in FIG. 5) of the drive rod 12 extends outside the wall via a bearing device 16 and has a connecting portion 17 at the outer end portion. Although not shown, the connecting portion 17 is interlockingly connected to a driving device such as a governor which drives in accordance with the number of rotations. As a result, as the number of rotations increases, the connecting portion 17 moves from the state of FIG. 9 in the direction of arrow A1. ,
The state shown in FIG.

A pair of left and right first rack teeth 14 are formed on the surface of the drive rod 12 on the cylinder side, and second rack teeth 15 are formed on the tip end side (the left side in FIG. 5) of the surface opposite to the cylinder side. ing.
Each sub-valve 6 is arranged on the cylinder side of the drive rod 12 and integrally has a drive pinion 10 on the upper side thereof, and the drive pinion 10 on one side (the left side in FIG. 5) is the first rack of the direct drive rod 12. The drive pinion 10 on the other side (connecting portion 17 side) meshes with the tooth 14, and meshes with the first rack tooth 14 via a reversing gear 18.

One idle gear 20 for driving the main valve is arranged at a position opposite to the cylinder side with respect to the drive rack 12 and only on one side of the main exhaust passage 2, and the gear is supported in a posture parallel to the sub valve 6. It is rotatably housed in the hole 20a and meshes with the second rack teeth 15 of the drive rod 12.

In FIG. 1, the upper shaft portion of the idle gear 20 is a collar 36.
It is supported by the gear support hole 20a via.

On the upper wall in the middle of the main exhaust passage 2, a pair of downwardly inclined valve holes 21 opening toward the cylinder 1 side is formed, and each main valve 5 is slidable in each valve hole 21. It is fitted.

In FIG. 2, a pair of left and right valve holes 21 each have a horizontally long oval cross section, and each main valve 5 has an oval cross section corresponding to the valve hole 21. The dimensional accuracy of fitting between 21 and the outer peripheral surface of the main valve is so precise that exhaust gas does not pass through.

As shown in FIG. 3, each valve hole 21 communicates with one guide recess 25 at the end portion (right side in FIG. 3) opposite to the cylinder side. Are connected by a connecting pin 28 so that they can move integrally. The tip end of the main valve 5 on the cylinder side is formed in an arc shape corresponding to the shape of the inner peripheral surface of the cylinder.
Rack teeth 30 are formed on the side surface of one of the main valves 5 in the lengthwise direction of the main valve.

The rack teeth 30 of the main valve 5 are carved in parallel with the cylinder center line as shown in FIG. 1, and mesh with the idle gear 20. The rack teeth 30 are formed at a position where they are not exposed to the main exhaust passage 2 at least near the time when the main valve is fully opened. When the main valve is fully opened, the elliptical tip portion fits around the entire opening of the valve hole 21. In addition, the exhaust gas is prevented from entering (see FIG. 2).

In FIG. 6, the upper shaft portion of the sub-valve 6 is supported in the support hole 6a via the collar 35.

The operation will be described. At low speed rotation, the drive rod 12 is pushed into the hole 13 as shown in FIG. 9, and the main valve 5 projects forward and downward into the exhaust passage 2 as shown in FIG. It is in a state of being substantially along the inner peripheral surface. As a result, the upper portion of the main exhaust passage 2 is closed, the exhaust passage cross-sectional area is reduced, and the exhaust timing is delayed. On the other hand, the sub valve 6 closes the sub exhaust passage 3 as shown in FIGS. 8 and 10. Therefore, when viewed as the entire exhaust passage, the exhaust cross-sectional area becomes small corresponding to the low speed, and the exhaust timing becomes slow corresponding to the low speed.

When the rotational speed of the engine increases, the drive rod 12 shown in FIG. 9 moves in the A1 direction by the operation of the governor. As a result, the main valve 5 in FIG. 7 moves in the opening direction via the idle gear 20, and begins to retract from the main exhaust passage 2 into the valve hole 21. Also, the sub valve 6 in FIG. 8 also rotates in the opening direction,
Start opening the auxiliary exhaust passage 3. In this way, the exhaust gas is exhausted from the auxiliary exhaust passage 3 opened by an appropriate amount and the main exhaust passage 2 also opened by an appropriate amount, so that the total exhaust cross-sectional area becomes a size commensurate at the time of medium speed rotation, and the exhaust timing is also medium. It becomes faster in proportion to the speed.

When the rotation speed is further increased, the drive rod 12 moves in the direction of arrow A up to the maximum stroke as shown in FIG. As a result, as shown in FIG. 1, the main valve 5 is retracted to the substantially same plane as the upper wall surface of the exhaust passage 2 to be fully opened, and the sub valve 6 is also fully opened as shown in FIG. Since the exhaust gas is discharged through the main valve 5 and the sub valve 6 which are fully opened in this manner, the total exhaust passage cross-sectional area becomes a size commensurate with the high speed, and the exhaust timing is further advanced corresponding to the high speed.

When the main valve is fully opened, the inner peripheral surface of the opening of the valve hole 21 is sealed by the tip of the main valve 5 having an oval cross-section, so almost no exhaust gas enters the meshing portion with the idle gear 20. Without this, the output reduction due to the interference between the exhaust gases is prevented.

Further, since the main valve 5 meshes with the idle gear 20 on the side opposite to the cylinder side of the drive rod 12 and is far away from the cylinder when fully opened, the influence of heat inside the cylinder is small, and therefore the valve hole 21 and Even if the fitting dimension of the main valve 5 is precisely finished, it does not affect the operation of the main valve 5 due to thermal expansion or the like.

(Another embodiment) (1) A pair of (or one) resonators 37 as shown in FIG.
It is also possible to apply the present invention to a two-cycle engine in which the sub-valve 6 is used to close the auxiliary exhaust passage 3 at low speed and the resonator chamber 37 is opened to the main exhaust passage 2.

(2) Further, the main valve 5 may be a single structure without being divided into right and left.

(3) One pair of idle gears 20 may be provided on the left and right sides in FIG. 5, the rack teeth 30 of the main valve 5 may be formed on both sides, and the main valve may be driven by the left and right idle gears.

(Effects of the Invention) As described above, the present invention is: (1) The main valve 5 is a slide type that fits in the valve hole 21, and the second side of the surface of the drive rod 12 opposite to the cylinder side.
Since the idle gear 20 is meshed with the rack tooth 15 and the rack gear 30 on the side surface of the main valve 5 is meshed with the idle gear 20, the main valve 5 is driven. Since it is located far away from, the influence of the heat of the cylinder is reduced, the fitting dimensional accuracy of the main valve 5 and the valve hole 21 is improved, and it is possible to finish without rattling.

Moreover, the main valve 5 is not directly engaged with the sub valve 6,
By driving the main valve 5 from the drive rod 12 via the idle gear 20, the gear meshing portion is not exposed to the main exhaust passage unlike the conventional example of FIG.

Therefore, a gap around the main valve does not occur when fully opened, and the output during high-speed rotation can be further improved.

(2) Since the main valve 5 is of a slide type, the degree of freedom in changing stroke of the cross-sectional area of the main exhaust passage 2 is increased, and the degree of freedom in setting exhaust timing is increased.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of the main valve of a two-cycle engine to which the present invention is applied when the main valve is fully opened (I-I cross-sectional view of FIG. 4), FIG. 2 is a view taken along the arrow II of FIG. 1, and FIG. Fig. 1 is a III-III sectional view, Fig. 4 is a IV-IV sectional view of Fig. 1, Fig. 5 is a VV sectional partial view of Fig. 4, and Fig. 6 is VI-VI of Fig. 4. Sectional sectional view, FIG. 7 is a vertical sectional view when the main valve is closed, FIG. 8 is a sectional view taken along line VIII-VIII of FIG. 7 when the sub valve is closed, and FIG. 9 is the same part as FIG. 5 when the sub valve is closed. A sectional view, FIG. 10 is a sectional view taken along line XX of FIG. 8, FIG. 11 is a horizontal sectional view of another embodiment, and FIGS. 12 to 14 are longitudinal sectional views of a conventional example. 1 ... Cylinder, 2 ... Main exhaust passage, 3 ... Sub exhaust passage,
5 ... Main valve, 6 ... Sub valve, 10 ... Pinion, 12
... Drive rods, 14, 15 ... First and second rack teeth, 20 ... Idle gears, 21 ... Valve holes, 30 ... Rack teeth

Claims (1)

[Scope of utility model registration request] 1. A rotary sub-valve that forms a main exhaust passage and a sub-exhaust passage communicating with the inside of a cylinder, and opens and closes the sub-exhaust passage with respect to the main exhaust passage. A valve hole is formed facing downward and opening in a downward slope, a main valve is slidably fitted in the valve hole, and a drive rod for driving both valves is moved in the rod length direction according to the rotational speed. A first rack tooth is formed on the cylinder side of the drive rod and a second rack tooth is formed on the opposite side, the pinion of the sub valve is meshed with the first rack tooth, and the idle gear is meshed with the second rack tooth. ,
By forming rack teeth on the side surface of the main valve and meshing with the idle gear, and by moving the drive rod when the number of rotations increases, the main valve opens to increase the cross-sectional area of the main exhaust passage and simultaneously opens the sub valve. An exhaust system for a two-cycle engine, characterized in that the rack teeth of the main valve are not exposed in the main exhaust passage when the main valve is opened.