JPH0550577B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an intake system for an engine, and particularly to an intake system that increases the amount of intake air.

(Prior art) In general, in order to increase the intake air filling amount and improve output in engines, the opening timing of the intake valve at the transition from the intake stroke to the compression stroke is set to 40 to 60 degrees past the bottom dead center. The intake air is introduced into the combustion chamber by its own flow inertia even after the piston moves to the upward stroke. Attempts have been made to further increase the filling amount by increasing the length of the intake passage sufficiently to increase the inertia of intake air. However, this intake inertia effectively increases the charging amount only at high engine speeds when the flow of intake air in the intake passage is fast; cannot be improved.

Additionally, at low engine speeds, the flow of intake air is slow and the pressure in the intake passage near the combustion chamber is also low, so the intake valve closing timing is set well past bottom dead center as described above. If this happens, there is a problem that when the piston moves to the upward stroke, the intake air that has been introduced into the combustion chamber tends to flow back into the intake passage, making it difficult to secure a sufficient amount of charging at low rotation speeds. There is.

(Object of the Invention) The present invention deals with the above-mentioned actual situation regarding the intake system of an engine, and is intended to deal with the above-mentioned actual situation regarding the intake system of an engine. By increasing the flow velocity of intake air in the latter half of the transitional intake stroke, the amount of intake air filling is increased, and the backflow of intake air is prevented, especially at low engine speeds, thereby effectively increasing the amount of filling over the entire engine speed range. The purpose is to increase output and improve output.

(Structure of the Invention) That is, in order to achieve the above object, the engine intake system according to the present invention is provided with a passage control means that operates to narrow the cross-sectional area of the passage only in the latter half of the intake stroke in the downstream part of the intake passage. It is characterized by: This passage control means is constituted by, for example, a swingable plate member that forms part of the inner surface of the intake passage, and is configured to control the bottom dead center from the latter half of the intake stroke, that is, when the downward speed of the piston begins to slow down. It operates to narrow the cross-sectional area of the passage until the intake valve closes. Therefore, the flow rate of the intake air during the latter half of the intake stroke is increased while avoiding an increase in the flow resistance of the intake air during the first half of the intake stroke. As a result, the filling amount of intake air increases, and backflow of intake air is prevented at low engine speeds.

(Example) Hereinafter, an example of the present invention will be described based on the drawings.

As shown in FIG. 1, a combustion chamber 2 of an engine 1
are cylinder block 3 and cylinder head 4.
and a piston 5, and the combustion chamber 2 is communicated with intake and exhaust ports 6 and 7 provided in the cylinder head 4 through intake and exhaust valves 8 and 9, respectively. These intake and exhaust valves 8,
9 is connected by a camshaft 10 rotating in synchronization with a crankshaft (not shown) via rocker arms 11 and 12 and springs 13 and 1, respectively.
4 and is opened at a predetermined timing. In addition, an intake pipe 1 is provided in the intake port 6.
5 is connected, and an intake passage 18 is formed which extends from the air cleaner 16 to the combustion chamber 2 via the throttle valve 17, the inside of the intake pipe 15, and the inside of the intake port 6. Although not shown, an exhaust pipe is connected to the exhaust port 7.

A downstream portion of the intake passage 18 is provided with a passage control plate 19 that operates to narrow the cross-sectional area of the passage downstream. This passage control board 1
9 has an upstream end pivotally attached to the upper part of the pipe wall of the intake pipe 15 via a pin 20, and a downstream end located in the vicinity of the combustion chamber 2 in the intake port 6. It is arranged to reach
As shown by the solid line, when it swings most upwardly, it is positioned along the upper inner surface of the intake pipe 15 or the intake port 6, so that the cross-sectional area of the intake passage 18 is not narrowed, but as shown by the chain line, When swinging downward, the cross-sectional area of the downstream portion of the intake passage 18 is gradually narrowed in the flow direction. here,
As shown in FIG. 2, a notch 19a is provided at the downstream end of the passage control plate 19 to avoid interference with the stem portion of the intake valve 8.

As shown in FIGS. 1 and 2, a drive device 20 for swinging this passage control plate 19 includes a drive shaft 21 disposed above the intake pipe 15 in the direction of the crankshaft, and a drive shaft 21 disposed above the intake pipe 15 in the direction of the crankshaft. An eccentric pin 22 provided at a position corresponding to the intake passage 18 of each cylinder above, a connecting link 23 connected at one end to the pin 22, and an upper end connected to the other end of the link 23 and connected to the intake pipe 15. The crank mechanism includes a slide link 24 that slidably passes through the upper wall, and the lower end of the slide link 24 is connected to the upper surface of the passage control plate 19 via a bracket 19b. A belt (or chain) 27 is wound between pulleys 25 and 26 attached to one end of the drive shaft 21 and one end of the camshaft 10, respectively, and the drive shaft 21 is rotated in conjunction with the camshaft 10. As a result, the passage control plate 19 is reciprocated up and down via the crank mechanism. Here, the pulley 25,
26 are made equal in diameter so that the camshaft 10 and the drive shaft 21 rotate at the same rotational speed, and when the intake valve 8 starts to open, as shown by the symbol A in FIGS. The phases of the two shafts 10 and 21 are set so that the timing at which the passage control plate 19 starts lifting downward substantially coincides.

Next, the operation of the above embodiment will be explained.

Now, when engine 1 is running, piston 5
It is assumed that the engine is near top dead center and the intake stroke is about to start. At this time, as shown by the solid line in FIG. 1 and as shown by the symbol A in FIGS. 1 and 2, a passage control plate 19 provided in the intake passage 18
is at the uppermost position, that is, at the position where the passage 18 has the widest passage cross-sectional area. Therefore, when the intake air flows into the combustion chamber 2 through the intake passage 18 by opening the intake valve 8 and lowering the piston 5, the control plate 19 does not act as a flow resistance to the intake air, and the required amount of intake air is maintained. will flow into the combustion chamber 2. From this state, as the piston 5 descends, the passage control plate 19 is lifted downward from the crankshaft (not shown) via the camshaft 10 and the drive device 20, and as a result, the passage cross-sectional area of the intake passage 18 gradually increases. During the period from the time when the piston 5 passes through the bottom dead center, indicated by the symbol B in FIG. 3, until the time when the intake valve 8, indicated by the symbol C, is closed.
That is, in the latter half of the intake stroke, the downward list amount of the passage control plate 19 becomes approximately maximum, and the passage cross-sectional area of the intake passage 18 is narrowed to approximately the maximum extent. Therefore, even though the intake flow rate decreases during this period, the flow velocity is maintained at a relatively high state, and along with this, the position immediately upstream of the intake valve 8 at the downstream end of the intake passage 18 pressure will increase. As a result, an inertial supercharging effect is obtained in the latter half of the intake stroke, increasing the intake air filling amount, and at the same time, backflow of intake air in the latter half of the intake stroke is prevented, particularly at low engine speeds.

Here, to explain the experimental results conducted for this example, first, as shown in FIGS. 3 and 4, when the engine 1 is at high speed, the intake air flow velocity from the middle to the latter half of the intake stroke is The pressure in this embodiment shown by the curve is higher than that in the curve, and accordingly, the peak value of the pulsation in the passage pressure at the position immediately upstream of the intake valve during the latter half of the intake stroke is also higher. In addition, as shown in Figures 5 and 6, even at low rotation speeds, the flow velocity and pressure in the second half of the intake stroke of this embodiment, shown by the curve, are lower than that of the conventional model, which is shown by the curve. And both are getting higher. In this way, the intake air filling efficiency is increased over the entire engine speed range.

In the above embodiment, the passage control plate 19 is configured to be operated mechanically in conjunction with the camshaft 10, but the control plate 19 may be operated electrically, for example, or the passage cross-sectional area may be changed. The means for narrowing in the flow direction is not limited to the configuration in which the control plate is oscillated as shown in the embodiment.

(Effects of the Invention) As described above, according to the present invention, there is provided a passage control means in the downstream part of the intake passage that narrows the passage cross-sectional area of the passage only in the latter half of the intake stroke to increase the flow velocity of intake air. Therefore, the amount of intake air filling is increased in the entire rotation range of the engine, and backflow of intake air in the latter half of the intake stroke, especially at low engine speeds, is prevented. As a result, the intake air filling amount is increased not only at high engine speeds, but also at low engine speeds, where it has been difficult to increase the intake air filling amount in the past, and the output is improved over a wide range of engine operation.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention; FIG. 1 is a vertical sectional view of the main parts of the engine, FIG. 2 is a plan view of the passage control means, and FIG. 3 is a graph showing the effects. 18... Intake passage, 19... Passage control means (passage control board).

Claims (1)

[Claims] 1. An intake system for an engine, characterized in that a passage control means for narrowing the passage cross-sectional area only in the latter half of the intake stroke is provided in the downstream part of the intake passage.