JPH05180084A - Carburetor - Google Patents

Abstract

PURPOSE:To provide a desired pulsation effect and sufficient acceleration by detecting an accelerating condition of a car body in a high speed region, and changing a preset value transferred to the lower speed side in accordance with larger increasing this acceleration. CONSTITUTION:A power system fuel passage 39, which supplies fuel 26 in a float chamber 25 to an intake passage 24 in accordance with its intake negative pressure, is provided. An opening/closing valve 41, by which a halfwary part of the power system fuel passage 39 can be opened and closed, is provided, and when a speed of an engine 12 reaches a preset value in a high speed region, the opening/closing valve 41 is closed. An accelerating condition of a car body is detected particularly in the high speed region, and the preset value is transferred to a side of the lower speed in accordance with larger increasing this acceleration. In this way, in the high speed region, the larger is a speed increasing rate of the engine 12, the opening/closing valve 41 is closed in the earlier stage of a process of increasing the engine speed, and a supply amount of fuel is decreased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carburetor for a two-cycle engine mounted on, for example, a motorcycle, and more particularly to a carburetor having a power system fuel passage.

[0002]

2. Description of the Related Art Many carburetors are provided with a power system fuel passage for supplying the fuel in the float chamber to the intake passage according to the magnitude of the intake negative pressure in the intake passage. By the way, when the engine speed is in the high speed range, the intake negative pressure in the intake passage becomes extremely high, so that the amount of fuel supplied to the intake passage through the power system fuel passage tends to be excessive. Therefore, if the above configuration is maintained, the output may be reduced due to excessive fuel in the high speed range. Therefore, in the above-mentioned conventional configuration, an opening / closing valve is provided that can open and close a midway portion of the power system fuel passage, and when the engine speed reaches a set value in the high speed range, the opening / closing valve is closed to set the power There is a system in which the fuel supply through the system fuel passage is stopped to prevent the fuel supply amount from becoming excessive.

[0003]

However, the above-mentioned conventional structure has the following problems. That is, in the above high speed range, the engine speed increase rate (rotation speed per unit time = rpm / s, the same applies hereinafter), which is an example of vehicle body acceleration, is small, that is, the engine speed gradually increases. If so, the exhaust gas temperature also rises in accordance with this rise. Therefore, this exhaust provides a desired pulsating effect. However, in the high speed range, the rate of increase in the number of revolutions is large, that is, when the number of revolutions rises sharply, the exhaust gas temperature does not rise in response to this rise. Is not obtained enough,
Therefore, there is a problem that the output in the high speed range is reduced and the acceleration performance becomes insufficient.

[0004]

SUMMARY OF THE INVENTION The present invention has been made by paying attention to the above circumstances. When the acceleration of the vehicle body is large in the high speed range of the engine speed, the temperature of the exhaust gas is rapidly changed according to this magnitude. The purpose is to raise it to obtain a desired pulsating effect, and thus to obtain sufficient acceleration.

[0005]

To achieve the above object, the present invention is characterized in that the power for supplying the fuel in the float chamber to the intake passage in accordance with the magnitude of the intake negative pressure in the intake passage. A system fuel passage is provided, and an on-off valve is provided to open and close the middle part of the power system fuel passage.When the engine speed reaches a set value in the high speed range, the on-off valve is closed. In the container, the acceleration state of the vehicle body in the high speed range is detected, and the greater the acceleration, the more the set value is shifted to the lower speed side.

[0006]

[Operation] The operation of the above configuration is as follows. Depending on the magnitude of the intake negative pressure in the intake passage 24, the float chamber 25
A power system fuel passage 39 for supplying the fuel 26 of the same to the intake passage 24 is provided, and an opening / closing valve 41 for opening and closing a midway portion of the power system fuel passage 39 is provided, and a rotation speed of the engine 12 is a set value in a high speed range. In the carburetor 17 configured to close the opening / closing valve 41, the acceleration state of the vehicle body in the high speed range is detected, and the larger the acceleration, the more the set value is shifted to the lower speed side. I am doing it. For this reason, in the high speed range, as the rotation speed increase rate of the engine 12 is larger, the opening / closing valve 41 is closed earlier in the process of increasing the rotation speed, and the fuel supply amount is reduced (H in FIG. 1). Part). That is, the air-fuel ratio is set to the lean side (part I in FIG. 1), and the exhaust temperature rises accordingly. Therefore, when the rotation speed of the engine 12 suddenly increases, the temperature of the exhaust gas 47 rises without being delayed, and the pulsating effect of the exhaust gas 47 can be sufficiently obtained.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 2, reference numeral 1 is a motorcycle, a front fork 3 is rotatably supported at a front end of a body frame 2 of the motorcycle 1, and a front wheel 4 is supported at a lower end of the front fork 3. A handle 5 is attached to the upper end of the front fork 3. At the rear lower end of the vehicle body frame 2, a rear arm 8 is pivotally supported by a pivot shaft 7 so as to be vertically swingable, and a rear wheel 9 is supported at a swing end of the rear arm 8. 10 is a shock absorber. A seat 11 is supported on the rear portion of the body frame 2.

A two-cycle engine 12 is supported on the vehicle body frame 2, and the power of the engine 12 is transmitted to the rear wheel 9 via a transmission 13 and a chain winding device. The engine 12 includes a crankcase 14 and a cylinder 15 protruding from the crankcase 14 toward the front upper side. A reed valve (not shown), an intake pipe 16, and a carburetor 17 are sequentially connected to the intake port of the crankcase 14, while an exhaust pipe 18 extends from the exhaust port of the cylinder 15. 20 is a fuel tank and 21 is a radiator.

In FIG. 3, the carburetor 17 has a carburetor body 23, and an intake passage 24 is provided in the carburetor body 23. A float chamber 25 is formed in the lower portion of the carburetor body 23, and fuel 26 is supplied from the fuel tank 20 to the float chamber 25.

A sliding throttle valve 27 is provided on the upper wall of the intake passage 24.
Is slidably inserted in the vertical direction, and a venturi portion 28 is formed below the sliding throttle valve 27 in the intake passage 24.
Further, a main nozzle 29 connected to the float chamber 25 is formed on the lower wall of the intake passage 24 in the venturi portion 28. A needle valve 30 is projected from the lower end of the sliding throttle valve 27, and the needle valve 30 is fitted in the main nozzle 29.

The sliding throttle valve 27 is the throttle wire 3
1 is connected to an accelerator grip provided on the handle 5. By operating this accelerator grip, the sliding throttle valve 27 can be moved up and down.
If 7 is raised, the needle valve that rises with this rise is pulled out from the main nozzle 29, and the opening degree of the main nozzle 29 increases.

On the upper surface of the carburetor main body 23 on the upstream end side, a cylindrical support body 33 having a longitudinal axis is removably screwed by bolts 34. A nozzle pipe 35 extends downward from the lower portion of the inner hole of the support body 33. The lower end side of the nozzle pipe 35 penetrates the carburetor main body 23, and the nozzle 36 formed at the lower end of the nozzle pipe 35 is located substantially on the axial center of the intake passage 24 and opens toward the downstream side. There is. The float chamber 25 is connected to the upper portion of the support 33 by a tube 37. Further, a power jet 38 is attached inside the support 33.

The inner holes of the support member 33, the nozzle pipe 35, the tube 37, and the power jet 38 constitute a power system fuel passage 39, and the float depending on the magnitude of the intake negative pressure of the intake passage 24. Fuel 26 in the chamber 25 is supplied to the intake passage 24.

A solenoid valve type opening / closing valve 41 is attached to the upper portion of the support body 33, and a valve body 41a of the opening / closing valve 41 can open and close a middle portion of the power system fuel passage 39. The on-off valve 41 is electrically connected to the electronic control unit 42. Further, there is provided a sensor 43 that detects the rotation speed of the engine 12 and the rotation speed increase rate of the engine 12, which is an example of the acceleration state of the vehicle body, and outputs it to the control device 42. In addition, 44 is an O-ring,
The O-ring 44 prevents the fuel flowing toward the intake passage 24 from leaking to the outside.

When the engine 12 is operating, the outside air 45 is drawn into the intake passage 24. At this time, the sliding throttle valve 27
The fuel 26 in the float chamber 25 is supplied to the intake passage 24 through the main nozzle 29 and the power system fuel passage 39 in accordance with the magnitude of the intake negative pressure in the intake passage 24 based on the operation.

Then, the mixture 46 of the outside air 45 and the fuel 26 is sucked into the crankcase 14 through the intake pipe 16 and the reed valve and is pre-compressed therein. next,
This pre-compressed air-fuel mixture 46 is drawn into the cylinder 15 through the scavenging port, where it burns and the engine 12
Is used for output. Further, as shown in FIG. 2, the exhaust 47 after the combustion is exhausted through the exhaust pipe 18.

In FIGS. 1 and 3, when the rotational speed of the engine 12 is in the high speed range (A range in FIG. 1), the intake negative pressure in the intake passage 24 becomes extremely high, and the power system fuel passage 3
The amount of fuel 26 supplied to the intake passage 24 through 9 tends to be excessive. That is, if the power system fuel passage 39 is left open in the high speed region, the air-fuel ratio becomes richer in the range where the air-fuel ratio is smaller than the theoretical air-fuel ratio (B part in FIG. 1).
Same as above, the output decreases in the high speed range (C portion in FIG. 1).

Therefore, when the number of revolutions of the engine 12 reaches a preset value in the high speed range (D portion in FIG. 1) preset by the control device 42, the output of the sensor 43 which detects the number of revolutions of the engine 12 is output. By the signal, the on-off valve 41 is automatically closed via the control device 42, and the supply of the fuel 26 through the power system fuel passage 39 is stopped. Thus, the lean side, that is, the rich side is prevented in the range where the air-fuel ratio is smaller than the stoichiometric air-fuel ratio (part E in FIG. 1), and the output is improved (F in FIG. 1). Part).

In the high speed range, the engine 12
The higher the rotation speed increase rate, the more the set value of the rotation speed of the engine 12 for closing the opening / closing valve 41 is shifted to the low speed side.

This will be described more specifically with reference to FIGS. 1 and 4. In the control device 42, it is assumed that the set values of the rotation speed increase rate of the engine 12 are ΔN ₁ , ΔN ₂ , and ΔN ₃ , and that the relationship of ΔN ₁ <ΔN ₂ <ΔN ₃ is satisfied. In addition, the rate of increase in the rotation speed of the engine 12 at a certain point is
Let N. In this way, (1) If ΔN <ΔN ₁ , when the number of revolutions of the engine 12 reaches the set value (D in FIG. 1 and FIG. 4), the on-off valve 41 is operated as described above. Is closed and the supply of the fuel 26 through the power system fuel passage 39 is stopped.

(2) If ΔN ₁ <ΔN <ΔN ₂ , the set value of the engine speed (D portion in FIGS. 1 and 4) is on the low speed side (arrow G in FIGS. 1 and 4). Direction), and when the set value of the smaller value (H in FIGS. 1 and 4) is set,
1 is closed and the supply of fuel 26 is stopped. Then, the air-fuel ratio becomes lean (see I in Fig. 1).
Part), the temperature of the exhaust gas 47 will rise accordingly.
Therefore, even when the rotation speed of the engine 12 suddenly increases, such as when the throttle is fully opened, the exhaust gas 47 is not delayed.
Therefore, the pulsating effect of the exhaust gas 47 is sufficiently obtained. Therefore, as compared with the acceleration performance (J portion in FIG. 5) when the rotation speed increase rate in the high speed range is large and the temperature of the exhaust gas 47 cannot follow this and the pulsation effect is insufficient. According to the configuration, the output in the high speed range is sufficiently secured, and the sufficient acceleration performance is obtained (K portion in FIG. 5).

(3) If ΔN ₂ <ΔN <ΔN ₃ , the same as the above, the set value of the engine speed of the engine 12 is further shifted to the lower speed side, and the set value of the smaller value (in FIG. 4). L part), and sufficient acceleration can be obtained in the same manner as described above.

(4) If ΔN ₃ <ΔN, the rotational speed of the engine 12 is shifted to a lower speed side and set to a smaller set value (M part in FIG. 4). Also in this case, sufficient acceleration can be obtained as described above. After the on-off valve 41 is closed, the hysteresis is set to return to the open state when the number of revolutions of the engine 12 becomes smaller than the set value of the number of revolutions of the engine 12 when the valve is closed. ing.

In FIG. 3, an adjusting plate 48 and a sealing material 49 are provided between the carburetor main body 23 and the support body 33. If these are replaced with those having different thicknesses, the upper and lower sides of the nozzle 36 can be changed. The position is adjustable.

Although the above is based on the illustrated example, the acceleration state of the vehicle body may be detected by a combination of the speed change state of the power transmission device 13 and the open state of the sliding throttle valve 27. For example, when the reduction ratio of the power transmission device 13 is large and the sliding throttle valve 27 is fully open, it is determined that the acceleration is large. Also, the same as above, the acceleration state is due to changes in vehicle speed,
It may be detected based on the rotation speed increase rate of the front wheels 4 or the rear wheels 9.

[0026]

According to the present invention, the power system fuel passage for supplying the fuel in the float chamber to the intake passage is provided in accordance with the magnitude of the intake negative pressure in the intake passage. The carburetor is provided with an on-off valve that enables opening and closing, and when the engine speed reaches a set value in the high-speed range, the carburetor that closes the on-off valve detects the acceleration state of the vehicle body in the high-speed range. , The larger the acceleration, the more the above set value is changed to the lower speed side.Therefore, in the high speed range, the larger the engine speed increase rate, the faster the opening / closing valve in the process of increasing the engine speed. When closed, the fuel supply is reduced. That is, the air-fuel ratio is set to the lean side, and the exhaust gas temperature rises accordingly. Therefore, when the engine speed rapidly increases, the temperature of the exhaust gas rises without being delayed, and the pulsating effect of the exhaust gas can be sufficiently obtained.
Sufficient output is secured in the high speed range, and sufficient acceleration is obtained.

[Brief description of drawings]

FIG. 1 is a graph showing a relationship between an air-fuel ratio and an output with respect to an engine speed.

FIG. 2 is an overall side view of the motorcycle.

FIG. 3 is a sectional view of a vaporizer.

FIG. 4 is a graph showing a relationship between an opening / closing operation of an opening / closing valve and an engine speed.

FIG. 5 is a graph showing a relationship (acceleration) between engine speed and time.

[Explanation of symbols]

 12 engine 17 carburetor 24 intake passage 25 float chamber 26 fuel 39 power system fuel passage 41 on-off valve 42 control device 43 sensor 47 exhaust

Claims (1)

[Claims] 1. According to the magnitude of the intake negative pressure in the intake passage,
When a power system fuel passage for supplying the fuel in the float chamber to the intake passage is provided and an opening / closing valve that can open and close the middle part of the power system fuel passage is provided, when the engine speed reaches a set value in the high speed range. A carburetor in which the on-off valve is closed, wherein the acceleration state of the vehicle body in the high speed range is detected, and the larger the acceleration, the more the set value is shifted to the lower speed side.