JPH06212977A - Exhaust timing control device of two-cycle engine - Google Patents

Abstract

PURPOSE:To maintain a clearance between the edge of a valve element and a piston constant by moving the valve element in the axial direction of a cylinder bore, interlocking with a slider of an exhaust timing control valve and to avoid damage caused by heat by disposing a valve driving means on the lower dead point side from an exhaust port. CONSTITUTION:An exhaust timing control device 24 contains an exhaust timing control valve 25 for changing the height of the upper dead point side edge part in an opening part of an exhaust port 19. A planar slider 26 is disposed parallel to the axial direction of a cylinder bore 6 in such a manner as to freely slide in the axial direction in the valve 25. An exhaust through hole 28 where the exhaust port 19 passes through is bored in the slider 26, and a pent-roof like valve element 29 extended to the opening port side of the exhaust port 19 is disposed o the upper dead point side edge part thereof. The edge form 29a of the valve element 29 is made meet the curved form of the cylinder bore 6. A driving means 32 for sliding the valve 25 is disposed on the lower dead point side from the exhaust port 19. Accordingly, the exhaust timing can be changed steplessly according to the engine speed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust timing control device for a two-cycle engine in which the exhaust timing is changed according to the engine speed.

[0002]

2. Description of the Related Art Generally, in a two-cycle engine, if the exhaust timing is delayed at low speed and the exhaust timing is advanced as the engine speed increases, high output can be obtained over the entire engine speed range. It has been known.

7A and 7B are sectional views showing an example of a conventional exhaust timing control device for changing the exhaust timing. The exhaust timing control device 100 includes a cylinder bore 10
1, an exhaust timing control valve 103 for changing the height of the top dead center side edge portion of the exhaust port 102 opening to the inner wall surface of No. 1 is provided. The exhaust timing control valve 103 is slidably held in a sliding passage 104 that obliquely communicates with the exhaust port 102.

At the rear end of the exhaust timing control valve 103,
Control lever 106 that is rotated by rotation of the rotary shaft 105
The exhaust timing control valve 103 is slid by the rotation of the control lever 106. The rotating shaft 105 is driven by an actuator (not shown).

In FIG. 7A, the exhaust timing control valve 10 is shown.
Since the tip of 3 does not protrude from the sliding passage 104,
When the upper surface of the piston 107 descending from the top dead center side is lowered to the top dead center side edge portion (position A) of the opening of the exhaust port 102, the exhaust port 102 starts to open, and exhaust is started.

On the other hand, in FIG. 7B, the tip of the exhaust timing control valve 103 projects from the sliding passage 104, and its edge extends until it coincides with the inner wall surface of the cylinder bore 101. Therefore, the position of the top dead center side edge portion of the opening of the exhaust port 102 is substantially equal to the position of the exhaust timing control valve 103.
As a result, the exhaust timing is delayed by an amount corresponding to the difference from the A position.

The exhaust timing control device 100 is
When the engine speed of the two-cycle engine is high, the state shown in FIG. 7A is obtained. When the engine speed is low,
Since the control is performed so as to be in the state of FIG. 7 (b), the exhaust timing is set according to the engine speed, and the output and torque characteristics in each speed range are improved.

[0008]

However, in the case of the exhaust timing control device 100 having the above-described structure, when the exhaust timing control valve 103 is retracted from the position shown in FIG. Since the exhaust gas leaks from between the piston 107 and the circumferential surface of the piston 107, the actual exhaust timing becomes close to the state shown in FIG. 7A.

Therefore, the setting of the exhaust timing tends to be limited to only two types, one for high speed rotation and the other for low speed rotation, and it is difficult to set an intermediate exhaust timing, and at the same time, the exhaust timing is stepwise. Because of the switching, the output and torque characteristics are likely to fluctuate, and there is a risk that the operation of the two-cycle engine may not be smooth.

By the way, as shown in FIG. 7B, when the edge of the exhaust timing valve 103 reaches the inner wall surface of the cylinder bore 101, in order to prevent the exhaust leakage from between the edge and the piston 107, the edge is to be prevented. Should be as close to the piston 107 as possible without interfering with the piston 107. Therefore, it is necessary to process the edge with high accuracy.

However, since the shaft center of the exhaust timing control valve 103 is inclined with respect to the axial direction of the cylinder bore 101, the machining reference plane at the time of the above-mentioned edge machining is an inclined plane, and such a slanted machining is performed. Since it is necessary to perform the bending processing on the edge in accordance with the curved surface of the cylinder bore with reference to the reference surface, it is very difficult to improve the processing accuracy of the edge, and the processing cost increases.

Further, since the cooling water passage 108 provided around the cylinder bore 101 cannot be extended to the top dead center side of the exhaust port 102 where the heat load is maximum, the cooling effect at this portion is not good. There is a risk that the cylinder bore 101 may be distorted due to heat, and the exhaust timing control valve 103 may be galled.

The present invention has been made in order to solve the above-mentioned problems, and the exhaust timing can be changed steplessly according to the fluctuation of the engine speed, and the exhaust timing control valve can be easily processed and the exhaust timing can be improved. Accurate exhaust timing control can be performed by eliminating exhaust leakage between the timing control valve and piston.
Another object of the present invention is to provide an exhaust timing control device for a two-cycle engine that does not suffer from damage due to heat load.

Another object of the present invention is to form a flat inner wall surface in the exhaust port regardless of the movement of the exhaust timing control valve to smooth the flow of exhaust gas and improve engine output. An object is to provide an exhaust timing control device for a two-cycle engine.

[0015]

In order to achieve the above object, an exhaust timing control device for a two-cycle engine according to the present invention has a height of an edge portion on the top dead center side of an exhaust port opening which opens to an inner wall surface of a cylinder bore. In an exhaust timing control device for a two-cycle engine equipped with a variable exhaust timing control valve,
The exhaust timing control valve is configured such that an exhaust through hole through which the exhaust port passes is formed in a flat plate-shaped sliding body which is parallel to the axial direction of the cylinder bore and is slidable along the axial direction. An eave-shaped valve body extending toward the opening side of the exhaust port is provided at the top dead center side edge portion, and the edge shape of the valve body is configured to follow the curved surface shape of the cylinder bore. The valve driving means for sliding the valve is installed on the bottom dead center side of the exhaust port.

Further, at a position where the exhaust port passes through the exhaust through-hole, a wall surface constituting member forming an inner wall surface of the exhaust port on the bottom dead center side is passed through the exhaust through-hole. .

[0017]

When the exhaust timing control device for a two-cycle engine is constructed in this manner, as the sliding body of the exhaust timing control valve slides, the valve body moves along the axial direction of the cylinder bore. , The clearance between the edge of the valve body and the piston is kept constant. Therefore, the exhaust timing can be changed steplessly according to the change in the engine speed.

Further, since the sliding body is parallel to the axial direction of the cylinder bore, if one sliding surface of the sliding body is used as a machining reference surface, the edge of the valve body can be easily aligned with the curved surface of the cylinder bore for high precision. It can be curved. Therefore,
The clearance between the edge and the piston can be set to a minimum, exhaust leakage between the edge and the piston is prevented, and accurate exhaust timing control is performed.

Further, since the valve driving means is provided at the bottom dead center side of the exhaust port, the cooling water passage can be extended to the top dead center side of the exhaust port where the heat load is maximum, and the cooling around the exhaust port is possible. The effect is improved and heat damage is avoided.

Since the inner wall surface on the bottom dead center side of the exhaust port is kept flat regardless of the movement of the exhaust timing control valve, the flow of exhaust gas is not disturbed and the output and torque characteristics of the two-cycle engine are eliminated. Is improved.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a vertical sectional view of a two-cycle engine to which the present invention is applied. This 2 cycle engine 1
Is a water-cooled single-cylinder type mounted on a motorcycle, for example, and has a structure in which a cylinder block 3 and a cylinder head 4 are sequentially assembled on an upper part of a crankcase 2.

A cylinder liner 5 is provided in the cylinder block 3, and a cylinder bore 6 is formed in the cylinder liner 5. In addition, the cylinder head 4
Is formed with a combustion chamber 7 aligned with the cylinder bore 6, and a spark plug 8 is screwed into the central portion of the combustion chamber 7. In addition,
A cooling water passage 9 through which cooling water circulates is formed around the cylinder bore 6 and around the combustion chamber 7.

A piston 11 is slidably inserted into the cylinder bore 6, and a piston pin 12 provided on the piston 11 and a crank pin 14 of a crank shaft 13 rotatably supported in the crank case 2 are provided. Are connected by a connecting rod 15.

An intake port 16 is provided in the crankcase 2, and a reed valve 17 is installed inside the intake port 16. A carburetor (not shown) is connected to the intake port 16.

From the inside of the crankcase 2, a plurality of scavenging ports 18 rise along the cylinder liner 5, and these scavenging ports 18 are respectively in the cylinder bores 6.
There is an opening on the inner wall surface of the.

An exhaust port 19 is opened on the inner wall surface of the cylinder bore 6 at a position slightly higher than the scavenging port 18. The exhaust port 19 penetrates the cylinder block 3 and the valve holder 21 to the outside, and an exhaust muffler 22 is connected to the outlet thereof.

The exhaust port 19 is provided with an exhaust timing control device 24 according to the present invention. 2 (a), (b)
FIG. 4 is an enlarged view of the exhaust timing control device 24, showing an embodiment of the present invention. Further, FIG. 3 shows III-II of FIG.
2 is a sectional view taken along line IV-IV in FIG. 2A, FIG. 5 is a sectional view taken along arrows VL and VR in FIGS. 2A and 2B, and FIG. 6 is a VI-VI arrow view of FIG.

The exhaust timing control device 24 includes an exhaust port 1
An exhaust timing control valve 25 that changes the height of the top dead center side edge of the nine openings is provided. The exhaust timing control valve 25 is a flat plate-shaped sliding body 26 that is parallel to the axial direction of the cylinder bore 6 and is slidable along the axial direction.
have. The sliding body 26 has a sliding passage 27 (see FIG. 2) defined between the cylinder block 3 and the valve holder 21.
(Refer to (b)) It is held slidably without rattling.

An exhaust through hole 28 through which the exhaust port 19 passes is bored in the sliding body 26, and an eave extending toward the opening side of the exhaust port 19 is formed at the edge of the exhaust through port 28 at the top dead center side. The valve body 29 is provided. As shown in FIGS. 3 and 5, the exhaust port 19 is connected to the center bridge 3
Since it is divided into two parts on the left and right by 1, the pair of left and right valve elements 29 are also provided in accordance with this, and the cross-sectional shape thereof follows the upper surface shape of the passage of the exhaust port 19,
As shown in the left half of FIG. 2A and FIG.
The valve element 29 is in close contact with the upper surface of the passage of the exhaust port 19 when the valve is located at the uppermost position. Further, the shape of the edge (tip) 29a of the valve element 29 is such that the cylinder bore 6
R shape that matches the curved surface shape.

As shown in FIGS. 2 and 4, the exhaust timing control device 24 is provided with a drive means 32 for sliding the exhaust timing control valve 25. This drive means 32
Is installed on the bottom dead center side of the exhaust port 19,
For example, it is configured as follows.

At the bottom dead center side of the exhaust port 19, a laterally extending drive shaft 33 is rotatably supported. A pinion gear 34 is provided at one end of the drive shaft 33 and a pulley 35 is provided at the other end thereof. Each is provided integrally with rotation.
The pinion gear 34 meshes with a rack gear 36 formed on the sliding body 26. Further, the pulley 35 is
As shown in FIG. 6, it is placed in a pulley housing 37 formed in the valve holder 21 and a cable 39 of a cable mechanism 38 is wound. The cable mechanism 38 is
It is connected to an actuator (not shown), and the drive shaft 33 is rotationally driven by the actuator.

When the drive shaft 33 rotates, the pinion gear 34 moves the rack gear 36, and the exhaust timing control valve 25 slides. As a result, the valve element 29 changes the height of the top dead center side edge portion of the opening of the exhaust port 19 and the exhaust timing is changed. In the present embodiment, FIG. 2A shows a high speed rotation state in which the exhaust timing is the earliest, and FIG.
Indicates a low speed rotation state in which the exhaust timing is most delayed.

The exhaust timing control device 24 is
When the engine speed of the cycle engine 1 is low, the low speed rotation state is maintained, and as the engine speed increases, the high speed rotation state is controlled. At that time, the exhaust timing control valve 25 slides steplessly between the position shown in FIG. 2 (a) and the position shown in FIG. 2 (b).

By the way, the exhaust port 19 has the sliding member 2
6, the wall surface constituent member 41 forming the inner wall surface of the exhaust port 19 on the side of the bottom dead center passes through the exhaust through hole 28 together with the exhaust port 19, as shown in FIG. Has become. The wall surface component 41 is kept in a fixed position regardless of the movement of the exhaust timing control valve 25. In addition, in the present embodiment, the wall surface constituting material 41
Is integrally provided on the cylinder block 3 side, but may be integrally provided on the valve holder 21 side, for example.

In the exhaust timing control device 24 configured as described above, the valve body 29 moves along the axial direction of the cylinder bore 6 as the sliding body 26 of the exhaust timing control valve 25 slides. Regardless of the position of the moving body 26, the clearance between the edge 29a of the valve body 29 and the piston 11 is kept constant. Therefore, the exhaust timing can be changed steplessly according to the fluctuation of the engine speed, and the optimum output and torque characteristics can be obtained over the entire engine speed.
Moreover, since the exhaust timing does not change stepwise as in the conventional case, the operation of the two-cycle engine 1 becomes smooth.

Further, since the sliding body 26 is parallel to the axial direction of the cylinder bore 6, if one sliding surface of the sliding body 26, for example, the sliding surface 26a shown in FIG.
The edge 29a of 9 can be easily fitted to the curved surface of the cylinder bore 6 and curved with high precision. Therefore, the clearance between the edge 29a and the piston 11 can be set to a minimum, exhaust leakage between the edge 29a and the piston 11 can be prevented, and accurate exhaust timing control can be performed.

Further, since the valve driving means 32 is provided at the bottom dead center side of the exhaust port 19, the cooling water passage 9 can be extended to the top dead center side of the exhaust port 19 where the heat load becomes maximum. Become. Therefore, the cooling effect around the exhaust port 19 is improved, and damage due to heat load such as thermal distortion of the cylinder bore 6 and galling of the exhaust timing control valve 25 is avoided.

Further, regardless of the movement of the exhaust timing control valve 25, the wall surface constituting member 41 forming the inner wall surface of the exhaust port 19 on the side of the bottom dead center is kept in a fixed position, so that a step is formed on the bottom surface of the exhaust port 19. Is not generated, the flow of exhaust gas is not disturbed, and the output and torque characteristics of the two-cycle engine 1 are greatly improved.

In the state of FIG. 2B, the space 42 formed between the top dead center side edge portion of the exhaust port 19 and the valve element 29 communicates with the sliding passage 27, and the exhaust pressure is slid. Since it is released to the moving passage 27, the sliding body 26 is not strongly pressed against the valve holder 21 by the exhaust pressure. Therefore, the surface pressure applied to the sliding surface 26a of the sliding body 26 becomes extremely small, the risk of galling of the sliding body 26 disappears, and the operation of the exhaust timing control valve 25 becomes smooth.

[0041]

As described above, the exhaust timing control system for a two-cycle engine according to the present invention controls the exhaust timing by changing the height of the top dead center edge of the exhaust port opening that opens to the inner wall of the cylinder bore. In a two-cycle engine exhaust timing control device equipped with a valve, the exhaust timing control valve is configured such that the exhaust port is provided on a flat plate-like sliding body that is slidable along the axial direction of the cylinder bore. An exhaust through-hole is formed to allow passage of the exhaust through-hole, and an eave-shaped valve element extending toward the opening side of the exhaust port is provided at the top dead center side edge of the exhaust through-hole, and the edge shape of the valve element is the curved surface of the cylinder bore. And a valve drive means for sliding the exhaust timing control valve is installed closer to the bottom dead center side than the exhaust port.

Therefore, as the sliding body of the exhaust timing control valve slides, the valve body moves along the axial direction of the cylinder bore, so that the clearance between the edge of the valve body and the piston is irrespective of the position of the sliding body. Is kept constant. Therefore, the exhaust timing can be changed steplessly according to the change in the engine speed.

Further, since the sliding body is parallel to the axial direction of the cylinder bore, if one sliding surface of the sliding body is used as a machining reference surface, the edge of the valve body can be easily aligned with the curved surface of the cylinder bore for high precision. It can be curved. Therefore,
The clearance between the edge and the piston can be set to a minimum, exhaust leakage between the edge and the piston is prevented, and accurate exhaust timing control is performed.

Further, since the valve driving means is provided at the bottom dead center side of the exhaust port, the cooling water passage can be extended to the top dead center side of the exhaust port where the heat load is maximum, and the cooling around the exhaust port is possible. The effect is improved and heat damage is avoided.

Since the inner wall surface of the exhaust port on the bottom dead center side is kept flat regardless of the movement of the exhaust timing control valve, the flow of exhaust gas is not disturbed and the output and torque characteristics of the two-cycle engine are eliminated. Is improved.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a two-cycle engine to which the present invention is applied.

2A and 2B show an embodiment of the present invention, FIG. 2A is a diagram showing a high speed state of an exhaust timing control device, and FIG. 2B is a diagram showing a low speed state of an exhaust timing control device.

FIG. 3 is a sectional view taken along line III-III in FIG.

FIG. 4 is a sectional view taken along line IV-IV in FIG.

FIG. 5 is a view taken along arrows VL and VR in FIGS. 2 (a) and 2 (b).

6 is a view on arrow VI-VI in FIG. 4.

7A and 7B show a conventional technique, in which FIG. 7A is a diagram showing a high speed state of an exhaust timing control device, and FIG. 7B is a diagram showing a low speed state of an exhaust timing control device.

[Explanation of symbols]

 1 2 Cycle Engine 6 Cylinder Bore 19 Exhaust Port 24 Exhaust Timing Control Device 25 Exhaust Timing Control Valve 26 Sliding Body 27 Sliding Passage 28 Exhaust Through Port 29 Valve Disc 29a Edge of Valve Disc 32 Drive Means 41 Wall Surface Material

Claims (2)

[Claims] 1. An exhaust timing control device for a two-cycle engine, comprising an exhaust timing control valve for changing a height of a top dead center side edge portion of an exhaust port opening which opens to an inner wall surface of a cylinder bore. A flat plate-shaped sliding body that is parallel to the axial direction of the cylinder bore and is slidable along the axial direction is provided with an exhaust through hole through which the exhaust port passes. A valve element that has an eaves shape that extends toward the opening of the exhaust port, and the edge shape of the valve element conforms to the curved surface of the cylinder bore, and a valve drive that slides this exhaust timing control valve. An exhaust timing control device for a two-cycle engine, wherein the means is installed on the bottom dead center side of the exhaust port. 2. The wall component constituting the inner wall surface on the bottom dead center side of the exhaust port is passed through the exhaust through hole at a position where the exhaust port passes through the exhaust through hole. An exhaust timing control device for the two-cycle engine described.