JPH073176B2 - Intake device for 4-cycle internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a single combustion chamber in which a plurality of intake passages are connected to each other.
The present invention relates to a cycle internal combustion engine, and more particularly to an intake system for the same.

[Low technical background of the invention and its problems]

In this type of intake device, a single combustion chamber is connected to a low speed intake passage and a high speed intake passage, and a forced opening / closing type first carburetor is provided in the low speed intake passage. It is known that a negative pressure actuated second carburetor is provided in the intake passage for high speed. Then, in this intake device, at the time of low load operation with a small slot opening, only the first carburetor is opened, and when the engine shifts to high load operation,
The second carburetor is also opened in response to the increase in the suction negative pressure.

By the way, in the second carburetor, the piston valve for varying the venturi is operated by the pressure difference between the suction negative pressure and the return spring, so that the rise of the piston valve opening is gentle with respect to the increase of the rotational speed. It becomes a characteristic. Therefore, unless the rotational speed of the second carburetor is set lower by that amount, the torque may temporarily drop at the time of shifting to the high rotation and high load operation. As a result, the torque of the first carburetor and the second carburetor may be reduced. Since the rotation range in which the mechanical device overlaps and opens becomes longer, the torque at low and medium speeds when only the first carburetor is operating cannot be used effectively, and there is room for improvement in terms of output. Is left.

Further, since the suction negative pressure has a large variation factor, it is difficult to set the opening / closing timing of the second carburetor with respect to the engine speed, and there is also a large amount of variation, which makes setting difficult.

[Object of the Invention]

The present invention has been made based on such a circumstance. A high torque can be maintained at low and medium speeds, and this torque can be effectively used. Moreover, the setting of the second carburetor can be easily performed, and the entire rev range can be obtained. An object of the present invention is to provide an intake system for a four-cycle internal combustion engine that can obtain stable torque characteristics throughout.

[Outline of Invention]

In order to achieve the above object, an intake system for a four-cycle internal combustion engine according to the present invention is arranged in a low speed intake passage and a high speed intake passage connected to a single combustion chamber, and in the low speed intake passage, A first carburetor having a throttle valve that is forcibly opened and closed in communication with a slot operation; and a throttle valve that is disposed in the high-speed intake passage and that is forcibly opened and closed in conjunction with throttle operation A second carburetor having a normally closed on-off valve located downstream of the throttle valve and the engine speed, and the detected engine speed reaches a preset value. And a control mechanism for actuating the opening / closing valve of the second carburetor in the opening direction.

Example of Invention

 The present invention will be described below based on an embodiment shown in the drawings.

In FIG. 1, 1 is a cylinder block, 2 is a cylinder head,
Reference numeral 3 denotes a piston, and a combustion chamber 5 is formed in the cylinder head 2 so as to correspond to the cylinder 4 in the cylinder block 1. The combustion chamber 5 has two intake ports 6,6 and two exhaust ports
7, 7 and 7 are explained, and these intake ports 6, 6 and exhaust ports 7, 7
Are opened and closed by intake valves 8 and 8 and exhaust valves 9 and 9 at a predetermined timing.

A low speed intake passage 10a and a high speed intake passage 10b communicate with the intake ports 6,6. Each of these intake passages 10a, 10b
The first carburetor 11 for low and medium rotations and the second carburetor 12 for high rotations are connected to the upstream ends of the above. As shown in FIG. 3, the carburetor 11 for low to medium speed rotation has a piston valve 14 as a throttle valve for changing the venturi diameter in a mixing passage 13 connected to the intake passage 10a. The protruding needle valve 15 is inserted into the main nozzle 17 that opens below the oil level in the float wheel 16. The piston valve 14 is connected to the throttle lever 19 via the rotating arm 18, and is forcibly opened / closed in conjunction with the operation of the throttle 20.

Further, the carburetor 12 for high rotation has a piston valve 22 as a throttle valve for changing the Venturi diameter in the mixing passage 21 connected to the intake passage 10b as shown in FIG. The protruding needle valve 23 is the main nozzle 24
Has been inserted inside. The main nozzle 24 communicates with the float chamber 16 of the first vaporizer 11 via a communication passage 25,
The carburetor 12 for high rotation and the carburetor 11 for low and medium rotation share the float chamber 16. The piston valve 22 is connected to the stottle lever 19 via a rotating arm 26 and an interlocking shaft 27, and the piston valve 22 of the carburetor 12 for high rotation is also forcibly opened and closed in conjunction with the throttle 20. Operated. Therefore, the opening degree of the piston valves 14 and 22 of both vaporizers 11 and 12 corresponds to the opening degree of the sroll 20 as shown in FIG. Further, in the mixing passage 21 of the carburetor 12 that swings at a high speed, a butterfly-type on-off valve 28 is provided downstream of the piston valve 22. This opening and closing base
As shown in FIG. 6, when the engine speed (rpm) 28 reaches a preset constant number N ₁ , 28 is operated in the opening direction by a command signal from a control mechanism 29 that detects this engine speed. In the case of the present embodiment, the engine speed is detected from the ignition pulse of the ignition unit 30, and when this detector signal reaches a predetermined level, the control unit 31 causes the valve shaft of the opening / closing valve 28. given operation command signal to the servo motor 33 connected to 32, has become a Yo is rotated successively in an opening direction in accordance with the valve shaft 32 to the rotational speed of the increase, when the opening and closing valve 28 is the rotational speed reaches N ₂ Fully open.

The intake pipes 34 and 35 are connected to the upstream ends of the mixing passages 13 and 21 of the carburetors 11 and 12, respectively, and the length of the intake pipe 34 corresponding to the carburetor 11 for low and medium rotations is , A carburetor for high revolutions that is set according to the intake inertia at low and medium revolutions
The length of the intake pipe 35 corresponding to 12 is set according to the intake inertia at the time of high rotation.

Next, the operation of the above configuration will be described.

Rotational speed of the engine does not reach the N ₁ at the time of low or medium rotational-off valve 28
Since the mixing passage 21 is closed, the air-fuel mixture is not supplied from the high-speed carburetor 12 and the mixer generated by the low-medium-speed carburetor 11 that works in conjunction with the throttle 20 is operated at a low speed. It is supplied into the combustion chamber 5 through the intake passage 10a and the intake port 6. At this time, since the intake port 6 is eccentric with respect to the center of the cylinder 4, the air-fuel mixture flows in the circumferential direction of the cylinder 4, and a strong vortex flow is generated. Therefore, the combustion efficiency is improved, and high torque is obtained at low and medium speeds as shown by the solid line in FIG.

On the other hand, when the carburetor 11 is fully opened and the engine speed shifts to high rotation operation exceeding N ₁ , this is controlled by the control mechanism 29.
Is detected, and the opening / closing valve 28 is forcibly opened in conjunction with the rotation speed. At this time, the piston valve 22 of the carburetor 12 for high rotation is
Since it is already fully open in conjunction with the throttle 20, when the open / close valve 28 is opened, the air-fuel mixture generated by the high speed carburetor 12 burns through the high speed intake passage 10b and the intake port 6. The gas is supplied to the chamber 5, and the filling efficiency of the air-fuel mixture is improved accordingly.

Therefore, as shown by the broken line in FIG. 7, after the number of revolutions reaches N1, a high torque is obtained compared to the case where the air-fuel mixture is supplied only by the low speed intake passage 10a. However, according to such an intake device, the opening / closing valve 28 of the carburetor 12 for high rotation is adapted to be opened / closed in association with the rotation speed of the engine, so the opening timing of the opening / closing valve 28 starts to open. It can be freely set according to the output characteristic at low and medium rotations, and the rising characteristic at valve opening can be made faster than in the case of using suction negative pressure. Therefore, it is possible to maintain high torque without lowering the torque during the transition period when the carburetor 12 is operated, and it is possible to utilize the torque at the time of low and medium rotation.

Moreover, since the opening / closing valve 28 is forcibly opened / closed in conjunction with the number of revolutions, the opening / closing timing does not fluctuate. Therefore, the carburetor 12 can be easily set and stable torque characteristics can always be obtained. To be

Further, even in the carburetor 12 for high speed rotation, since the forced opening / closing type piston valve 22 interlocking with the throttle 20 is provided upstream of the opening / closing valve 28, the control mechanism 29 should fail and the opening / closing valve 28 should be opened. Even if it remains open, if you return the throttle 20, the mixing passage 21
Can be forcibly closed by the piston valve 22.
Therefore, the carburetor 12 will not be left open, and the waste of fuel can be prevented.

〔The invention's effect〕

According to the present invention described in detail above, the timing at which the opening / closing valve of the second carburetor starts to open can be freely set in accordance with the output characteristics at the time of low / medium rotation. During the transition period when the on-off valve starts to open, the throttle valve upstream of the on-off valve has already been opened by the throttle operation. Therefore, when this on-off valve is opened, the generated air-fuel mixture is suddenly discharged at high speed. It is supplied to the combustion chamber through the intake passage, and the efficiency of filling the air-fuel mixture is improved accordingly. Therefore, as compared with the case of using the conventional negative pressure responsive carburetor that uses the negative suction pressure, the rising characteristic when the second carburetor is opened can be made faster.
The torque is not temporarily reduced during the transitional period in which the carburetor is operated, high torque can be maintained, and the torque when the first carburetor is operating can be effectively used.

Moreover, since the opening / closing valve of the second carburetor is forcibly opened / closed based on the engine speed, the opening / closing timing of this opening / closing valve fluctuates with respect to the engine speed or becomes unstable. Nothing. Therefore, the setting of the second carburetor can be easily performed, and stable torque characteristics can be constantly obtained over the entire rotation range.

Further, according to the above configuration, even if the control mechanism should fail and the on-off valve remains open, the throttle valve is forcibly closed when the throttle is returned, so the second carburetor is left open. There is also an advantage that waste of fuel can be prevented.

[Brief description of drawings]

The drawings show one embodiment of the present invention, in which FIG. 1 is a sectional view and FIG.
FIG. 4 is a sectional view of the intake system, FIG. 3 is a sectional view taken along the line III-III in FIG. 2, and FIG. 4 is a partially sectional front view of the carburetor.
FIG. 7 to FIG. 7 are characteristic charts of husband and wife. 5 ... Combustion chamber, 10a ... Intake passage for low speed, 10b ... Intake passage for high speed, 11 ... Vaporizer of FIG. 1, 12 ... Second vaporizer, 14, 22 ... Throttle valve (Piston valve), 20 ... Throttle, 29 ... Control mechanism.

Claims (1)

[Claims] 1. A low-speed intake passage and a high-speed intake passage connected to a single combustion chamber, and a throttle valve disposed in the low-speed intake passage and forcibly opened / closed in association with throttle operation. A first carburetor, a throttle valve disposed in the high-speed intake passage and forcibly opened / closed in conjunction with throttle operation, and a normally-closed type downstream of the throttle valve. Second with on-off valve
And a control mechanism for detecting the engine speed and activating the on-off valve of the second carburetor in the opening direction when the detected engine speed reaches a preset value. An intake device for a four-cycle internal combustion engine, comprising: