JP2709952B2 - Exhaust control method for two-stroke engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Object of the Invention (1) Industrial Field of the Invention The present invention relates to an exhaust control method for a two-cycle engine.

(2) Prior Art Conventionally, in order to improve the output of a two-stroke engine, a pressure wave is generated in the middle of an exhaust system connected to an exhaust port, and the pressure wave acts on the exhaust port. It is known from, for example, JP-A-48-16223.

(3) Problems to be Solved by the Invention By the way, in order to obtain an output peak in an engine high-speed rotation range, a position where a positive pressure wave and a negative pressure wave are generated in a high-speed engine rotation range where an exhaust port closes quickly is increased. It is desirable to set the position near the exhaust port to promote the introduction of fresh air into the combustion chamber by the negative pressure wave and to improve the charging efficiency by the positive pressure wave. However, in a state where the action timing of the positive pressure wave and the negative pressure wave to the exhaust port is set so that the maximum output is obtained in a certain set high speed rotation region, the set high speed rotation region when the throttle opening is small, and the setting thereof In the middle speed range, which is almost half the speed of the high speed range,
If the positive pressure wave acts on the exhaust port at the timing when the exhaust port is completely closed, the introduction of fresh air into the combustion chamber is hindered because the throttle opening is small, the proportion of fresh air in the combustion chamber decreases, and Ignition may be hindered and irregular combustion may occur.

The present invention has been made in view of such circumstances,
The pressure wave of the combustion gas is applied to the exhaust port to improve the output and to prevent irregular combustion.
It is an object of the present invention to provide a method for controlling exhaust of a cycle engine.

B. Configuration of the Invention (1) Means for Solving the Problems The method of the present invention comprises, in an exhaust system connected to an exhaust port of an engine body, a diffusion section for diffusing an exhaust gas flow, and a diffusion section downstream of the diffusion section. A convergence section for converging the exhaust gas flow is set by variably setting a position along the exhaust gas flow direction, and a positive pressure wave generated in the convergence section and the diffusion section and a negative pressure wave generated in the diffusion section are caused to act on the exhaust port. In order to maximize the engine output in the high-speed rotation region, a reference control position in which the positions along the exhaust gas flow direction of the diffusion section and the converging section are closer to the exhaust port as the engine rotates at a high speed is set in advance. Controls the positions of the diffusion unit and the convergence unit based on the reference control position. At least in the engine setting high-speed rotation range where the throttle opening is equal to or less than a predetermined value, at least the convergence unit is controlled by the reference control position. Control position is set downstream in the exhaust gas flow direction, and in the engine setting middle speed range where the throttle opening is equal to or less than the predetermined value, the diffusion unit and the converging unit are set upstream in the exhaust gas flow direction from the reference control position. It is characterized by doing.

(2) Operation According to the above method, the positive pressure wave generated in the converging section and the diffusing section and the negative pressure wave generated in the diffusing section are applied to the exhaust port to improve the engine output, and the throttle opening is set to a predetermined value. In the following engine-set high-speed rotation range and engine-set medium-speed rotation range, the timing at which the positive pressure wave acts on the exhaust port is shifted from the reference state, thereby preventing the introduction of fresh air into the combustion chamber.

(3) Embodiment Hereinafter, an embodiment of the present invention will be described with reference to the drawings. First, in FIG. 1, an inner surface of a cylinder block 1 constituting an engine body of a two-cycle engine E mounted on a motorcycle is provided with An exhaust port 3 is opened and closed by a piston 2 slidably fitted in the cylinder block 1. An exhaust timing control valve is provided above the exhaust port 3 to control the opening and closing timing of the exhaust port 3. 4 are provided. The exhaust system connected to the exhaust port 3 includes a first exhaust pipe 5 whose upstream end is connected to the exhaust port 3, and an expansion chamber 6.
Is formed inside and connected to the downstream end of the first exhaust pipe 5, and the second exhaust pipe 8 connected to the downstream end of the pipe member 7
And a muffler (not shown) further connected to the second exhaust pipe 8.

An exhaust timing control valve 4 provided in the exhaust port 3 is fixed to a drive shaft 10 rotatably disposed on the cylinder lock 1, and the drive shaft 10 controls a transmission means 11 composed of a pulley, a transmission wire and the like. Connected to the servo motor 12 via the
Further, the servo motor 12 is provided with a potentiometer 13 for detecting the operation amount of the servo motor 12, that is, the opening of the exhaust timing control valve 4.

2, the pipe member 7 is formed so that its cross-sectional area is larger than the cross-sectional area of the first exhaust pipe 5, and its upstream end is reduced toward the upstream side. A tapered tube portion 7a having a diameter is provided. At the upstream end in the expansion chamber 6 formed by the pipe member 7, the diameter increases toward the downstream side in the expansion chamber 6, and is formed basically in a conical shape. A guide tube 14 as a diffusion unit configured to be movable along 15 is provided, and an upstream end of the guide tube 14 is connected to a downstream end of the first exhaust pipe 5.

The guide tube 14 includes a fixed tube portion 16 connected to the first exhaust pipe 5.
And a movable cylindrical portion 17 movable along the exhaust gas flow direction 15. The fixed cylindrical portion 16 is formed in a conical shape having a smaller diameter toward the upstream side, and is fixed to the upstream end of the pipe member 7 so as to protrude from the upstream end. Is connected to the downstream end of the first exhaust pipe 5. The movable cylindrical portion 17 is provided so as to be movable along the exhaust gas flow direction 15 in the expansion chamber 6, and has a straight pipe portion 17 on the upstream side.
a and the downstream tapered tube portion 17b are integrally connected. The inner diameter of the straight pipe portion 17a is set slightly larger than the large-diameter end of the fixed cylindrical portion 16, that is, the outer diameter of the downstream end, and the straight pipe portion 17a slides on the large-diameter end outer surface of the fixed cylindrical portion 16. The stationary cylindrical portion 16 is disposed so as to surround the portion facing the expansion chamber 6 so as to move in the exhaust flow direction 15. Also taper tube section 17
b is formed in a conical shape whose diameter increases toward the downstream side along the exhaust gas flow direction 15, and its small-diameter end, that is, the upstream end, is coaxially coupled to the straight pipe portion 17a.

A drive shaft 18 having an axis perpendicular to the exhaust flow direction 15 is rotatably supported on the pipe member 7. A drive member 19 fixed to the drive shaft 18 is connected to a movable cylinder portion 17 of the guide cylinder 14. Is done. That is, the driving member 19 is formed so as to straddle the tapered tube portion 17b of the movable cylindrical portion 17, and the tapered tube portion 17b is connected to the driving member 19 via a pair of connecting pins 20 parallel to the driving shaft 18. Is done. Thus, the movable cylinder 17 moves in the exhaust flow direction 15 in response to the swinging motion of the drive member 19 due to the rotation of the drive shaft 18, and thereby the downstream end of the movable cylinder 17, that is, the downstream end of the guide cylinder 14. Move along the exhaust gas flow direction 15.

A pulley 21 is attached to the projecting end of the drive shaft 18 projecting from the pipe member 7.
The pulley 21 is connected to a servomotor 23 as a driving means via a transmission cable 22 such as a transmission wire. In addition, the servomotor 23 is provided with a potentiometer 24 for detecting the operation amount of the servomotor 23, that is, the position of the downstream end of the guide cylinder 14 in the expansion chamber 6.

3, the downstream end of the pipe member 7 is integrally provided with a tapered pipe portion 7b having a smaller diameter toward the downstream side along the exhaust gas flow direction 15. The second exhaust pipe 8 ,
The intermediate portion is fixed to the small-diameter end of the tapered tube portion 7b and protrudes into the expansion chamber 6. In addition, at the downstream end in the expansion chamber 6, the diameter increases toward the upstream side along the exhaust gas flow direction 15, and is basically formed in a conical shape, and serves as a converging portion connected to the second exhaust pipe 8. The reflection cylinder 25 is disposed so that its upstream end can move along the exhaust gas flow direction 15. That is, a cylindrical collar 26 is fitted to the downstream end of the reflection tube 25,
The collar 26 is slidably fitted on the outer periphery of the second exhaust pipe 8.

The drive shaft is attached to the taper tube portion 7b of the tube member 7.
A drive shaft 28 parallel to 18 is rotatably supported, and the drive shaft 28 is connected to a driven shaft 29 provided at a large-diameter end, that is, an upstream end of the reflecting cylinder 25 by a connecting rod 30. In addition, a notch 31 extending in the exhaust flow direction 15 is provided at the large-diameter end of the reflecting cylinder 25 to allow the connecting rod 30 to swing. Therefore, the connecting rod 30 swings in response to the rotation of the drive shaft 28, whereby the reflecting cylinder 25 moves along the exhaust gas flow direction 15.

A pulley 32 is fixed to an end of the drive shaft 28 protruding from the pipe member 7, and the pulley 32 is connected to a transmission cable such as a transmission wire.
It is connected to a servomotor 34 as a driving means via 33. In addition, the servomotor 34 is provided with a potentiometer 35 for detecting the operation amount of the servomotor 34, that is, the position of the upstream end of the reflecting tube 25 in the expansion chamber 6.

The operation of each of the servomotors 12, 23, 34 is controlled by the control means 37. The control means 37 includes an engine speed detector
The engine speed N _E detected at 38, the throttle opening θ _TH detected at the throttle opening detector 39, the exhaust temperature T _E detected at an exhaust temperature detector 40 detecting the exhaust temperature in the expansion chamber 6. , The engine cooling water temperature T _C detected by the cooling water temperature detector 41, the atmospheric temperature detected by the ambient temperature detector 42
T _A, operation quantity detection value of the servo motor 12,23,34 by potentiometer 13,24,35 with atmospheric pressure P _A that is detected by the atmospheric pressure detector 43 are input is input. Further, the operation of the solenoid valve 44 for controlling the amount of bleed air in the carburetor (not shown) and the operation of the oil pump 45 are controlled by the control means 37.

In this control means 37, the opening degree of the exhaust timing control valve 4, that is, the operation amount of the servo motor 12 is controlled in accordance with the engine operation state, and the downstream end position of the guide cylinder 14 is controlled so as to be moved in accordance with the engine load. The operation of the motor 23 is controlled, and the operation of the servomotor 34 is controlled to move the upstream end position of the reflection tube 25 according to the engine load.

Here, in the control means 37, a map for controlling the operation of the servo motors 23 and 34 is set in advance as shown in FIG. That operation of the servo motor 23, 34 is one in which is determined according to the engine speed N _E and the throttle opening theta _TH, more than _THO for example, 10% constant value theta throttle opening theta _TH is preset Sometimes, as shown in FIG. 4 (a), and as shown in FIG. 4 (b), when the throttle opening θ _TH is equal to or less than the predetermined value θ _THO ,
Amount operation are respectively set according to the engine speed N _E. In FIG. 4, the broken line indicates the amount of operation of the servomotor 23, and the solid line indicates the amount of operation of the servomotor 34. The servomotors 23 and 34 have the downstream end of the guide cylinder 14 and This is to move the upstream end of the reflecting cylinder 25 to the upstream side along the exhaust gas flow direction 15.

That is, the upstream end position of the downstream end position and the reflecting cylinder 25 of the guide cylinder 14, basically the engine speed N _E by the operation amount map of the servomotors 12 and 23 shown in FIG. 4 (a) is large It is controlled based on a reference control position that is located on the upstream side (close to the exhaust port 3) along the exhaust gas flow direction 15 when the throttle opening θ _TH is equal to or less than a predetermined value θ _THO . As shown in FIG. 4 (b), the engine setting high speed rotation range N _{EH1 to} N _EH2 (for example, 9000
110000 rpm) from the reference control position to the downstream side in the exhaust gas flow direction, and the engine setting high speed rotation range N _{EH1 to} N _{EH2 .}
Medium speed range N _{EM1 to} N which is almost half of the engine setting
_{At EM2} (for example, 4000 to 5000 rpm), control is performed so as to shift from the reference control position to the upstream side along the exhaust gas flow direction 15.

Incidentally, in the fourth figure, the operation amount of the two servo motors 12 and 23 in the range the engine speed N _E is lower (idle speed range smaller than) is set to be large, which, This is set so as to keep the compression ratio low and keep the startability of the two-cycle engine E good.

Next, the operation of this embodiment will be described. The combustion gas discharged from the exhaust port 3 is introduced while diffusing from the guide cylinder 14 into the expansion chamber 6, and a negative pressure wave is generated to act on the exhaust port 3. The positive pressure wave is generated by being converged from the expansion chamber 6 while being converged by the reflection tube 25, and propagated to the exhaust port 3 side. Thus, a positive pressure wave is also generated when the positive pressure wave is converged by the guide tube 12. Therefore, a composite wave of the positive pressure wave generated in the reflection tube 25 and the positive pressure wave generated in the guide tube 12 is generated by the exhaust port 3. Will work. By combining the timing at which the negative pressure wave and the positive pressure wave act on the exhaust port 3, that is, the distance control of the position where the negative pressure wave and the positive pressure wave are generated from the exhaust port 3 and the opening control of the exhaust timing control valve 4, are combined. Output can be improved.

First, by controlling the opening of the exhaust timing control valve 4 in accordance with the engine operating state, the output of the two-cycle engine E increases as indicated by a portion A shown by a diagonally left slanted line in FIG. Further, by controlling the downstream end position of the guide cylinder 14 in accordance with the engine load, the output of the two-cycle engine E becomes
In FIG. 5, it increases as indicated by a portion B indicated by oblique lines falling to the right. That is, in the low-load operation range of the two-cycle engine E, the downstream end of the guide cylinder 14 is on the downstream side along the exhaust gas flow direction 15, so that the exhaust gas is introduced into the expansion chamber 6 by the guide cylinder 14. The location of the generated negative pressure is located relatively downstream at the upstream end in the expansion chamber 6, and the negative pressure generating section is compared with the exhaust port 3 in response to the relatively long time interval between the exhaust and scavenging strokes. In the high-load operation range of the two-stroke engine E, the exhaust end is discharged by the guide cylinder 14 because the downstream end of the guide cylinder 14 is on the upstream side along the exhaust gas flow direction 15. The location where the negative pressure is generated as a result of being introduced into the chamber is located at a relatively upstream position at the upstream end in the expansion chamber 6, and corresponds to a relatively short time interval between the exhaust and scavenging strokes. The pressure generating part is relatively close to the exhaust port 3 Can be located, thus subjected to the fresh air introduction and combustion gas discharge corresponding to the engine operating state by controlling the position of the negative pressure generating portion, it is possible to improve the output of a two-stroke engine E. In addition, by controlling the upstream end position of the reflection tube 25 and the downstream end position of the guide tube 14 according to the engine load, 2
The output of the cycle engine E increases as shown by a portion C shown by oblique lines falling to the right in FIG. That is, in the low-load operation range of the two-cycle engine E, since the upstream end of the reflection tube 25 and the downstream end of the guide tube 14 are on the downstream side along the exhaust gas flow direction 15, the exhaust gas is generated by convergence in the reflection tube 25. The position where the positive pressure wave and the positive pressure wave generated by the convergence of the positive pressure wave in the guide cylinder 14 are relatively downstream at the downstream end in the expansion chamber 6, and the time interval between the exhaust and scavenging strokes is relatively long. Accordingly, the positive pressure generating portion can be located at a position relatively distant from the exhaust boat 3, and in the high-load operation range of the two-stroke engine E, the upstream end of the reflection tube 25 and the downstream end of the guide tube 14 Is located upstream along the exhaust gas flow direction 15, the positive pressure generating section can be located relatively close to the exhaust port 3 in response to the relatively short time interval between the exhaust and scavenging strokes. Of the negative pressure generator In addition to the position control, the fresh air introduction and the combustion gas discharge corresponding to the engine operation state are efficiently performed, and the output of the two-cycle engine E can be improved.

By the way, the state of the pressure wave near the exhaust port 3 is as shown in FIG. In FIG. 6, reference symbol EO indicates the opening timing of the exhaust port 3, SO indicates the opening timing of the scavenging port, and BDC
The bottom dead center of the piston 2, EC is interrupted timing of the exhaust port 3, SC is shows the cutoff timing of the scavenging port respectively, reference numerals A ^- curve indicated by the negative pressure wave generated in the guide cylinder 14, by the symbol B ⁺ The curve shown is a positive pressure wave generated in the guide tube 14, the curve denoted by C ⁺ is the positive pressure wave generated in the reflection tube 25, and the code D ⁺ is the aforementioned code.
It shows a composite wave of the positive pressure waves indicated by B ⁺ and C ⁺ .

Thus, when the throttle opening θ _TH exceeds the predetermined value θ _THO , as shown in FIG. 6A, the positive pressure wave D ⁺ acts on the exhaust port 3 at a time substantially corresponding to the cutoff time EC. ,
As a result, it is possible to improve the compression efficiency and improve the output. In addition the throttle opening theta _TH is a predetermined value theta _THO following in the engine setting side rotation range N _EM1 to N _EM2, as shown in FIG. 6 (b), fast exhaust port than the positive pressure wave D ⁺ is interrupted timing EC will be acting on the 3, the further the engine set high speed range N _EH1 to N _EH2, as shown in FIG. 6 (c), positive pressure wave D ⁺ is interrupted timing slow exhaust port than EC 3
Will work. Therefore, the throttle opening θ _TH
It is possible to prevent a positive pressure wave acting in a direction that prevents fresh air from being introduced into the combustion chamber in a state where the air pressure is small, from acting on the exhaust port 3, and to prevent irregular combustion from occurring.

In the above embodiment, the throttle opening θ _TH is set to the predetermined value θ.
Guide cylinder 1 at high engine speed range N _EH1 to N _EH2 with engine setting below _THO
Although the downstream end of 4 and the upstream end of the reflecting tube 25 are both shifted from the reference control position to the downstream side along the exhaust gas flow direction 15, only the reflecting tube 25 may be shifted.

C. Effects of the Invention As described above, according to the present invention, the positive pressure wave generated in the converging portion and the diffusing portion, and the negative pressure wave generated in the diffusing portion are caused to act on the exhaust port, thereby promoting the introduction of fresh air and the compression efficiency. By improving the engine output by improving the engine speed, the timing at which the positive pressure wave acts on the exhaust port in the engine setting high speed rotation range and the engine setting medium speed rotation range where the throttle opening is less than the predetermined value is shifted from the reference state. Irregular combustion can be prevented by preventing obstruction of introduction of fresh air into the combustion chamber.

[Brief description of the drawings]

1 shows an embodiment of the present invention. FIG. 1 is an overall schematic view showing an exhaust system of a two-stroke engine, and FIG.
3 is a sectional view taken along the line III-III in FIG. 1, FIG. 4 is a view showing a control map set in advance, FIG. 5 is an output characteristic chart, and FIG. It is a figure showing a state of a pressure wave near a port. DESCRIPTION OF SYMBOLS 1 ... Cylinder block as an engine main body, 3 ... Exhaust port, 14 ... Guide cylinder as a diffusion part, 15 ... Exhaust gas flow direction, 25 ... Reflection cylinder as a converging part, E ... 2-cycle engine

Continuation of the front page (72) Inventor Takumi Tottori 1-4-1 Chuo, Wako-shi, Saitama Pref. Honda Technical Research Institute Co., Ltd. (56) References JP-A-2-163411 (JP, A) JP-A-2-201020 (JP, A) JP-A-1-240726 (JP, A) JP-A-2-91414 (JP, A) JP-A-2-163410 (JP, A)

Claims (1)

(57) [Claims] An exhaust system connected to an exhaust port of an engine main body includes a diffusion portion for diffusing an exhaust gas flow and a converging portion for converging the exhaust gas flow downstream of the diffusion portion along an exhaust gas flow direction. The position is set to be variable, and the positive pressure wave generated in the converging section and the diffusing section, and the negative pressure wave generated in the diffusing section are caused to act on the exhaust port. A reference control position closer to the exhaust port is set in advance as the position of the converging portion along the exhaust gas flow direction becomes higher in engine speed, and basically the positions of the diffusing portion and the converging portion are set to the reference control position. In the engine setting high-speed rotation range where the throttle opening is equal to or less than a predetermined value, at least the convergence portion is set to the downstream side in the exhaust gas flow direction by the reference control position, and Liter opening the exhaust control method of a two-stroke engine, characterized by setting a spreading section and converging section to the exhaust gas flow direction upstream of the reference control position in the engine set speed rotation range is less than a predetermined value.