JPH0550574B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an intake system for an engine, and more particularly to a system that utilizes the intake inertia effect to improve output.

(Prior art) Conventionally, as seen in Japanese Patent Application Laid-open No. 48-58214, the length and cross-sectional area of the intake passage are changed according to the engine speed, thereby making use of pressure fluctuations in the intake passage. 2. Description of the Related Art Devices are known that increase suction efficiency in various engine speed ranges and improve output. In other words, pressure oscillations occur in the intake passage due to intermittent intake as the engine operates, so if positive pressure waves are introduced into the cylinder at the appropriate timing, the intake efficiency will be improved. can be increased. The timing at which positive pressure waves are introduced into the cylinder can be adjusted by the length of the intake passage, so by changing the length of the intake passage according to changes in engine operating conditions, various operating ranges can be adjusted. In,
The so-called dynamic effect of intake air, that is, the inertial effect and pulsation effect due to the above-mentioned development can be effectively utilized to increase the intake efficiency. Note that such a dynamic effect of intake air can also be adjusted by changing the cross-sectional area of the intake passage.

By the way, in conventional devices of this type, the opening and closing timing of the intake valve is fixed, and the BDC (piston bottom dead center)
The intake valve is closed after a predetermined crank angle delay. Under such conditions,
Even if tuning is performed to enhance the dynamic effect of positive pressure waves as much as possible by adjusting the length or cross-sectional area of the intake passage, the characteristics of the cylinder pressure may change due to engine operating conditions, for example, as the engine speed changes. As a result, at low speeds, the pressure inside the cylinder increases before the intake valve closes, causing blowback, and at high speeds, the intake valve closes even though the cylinder pressure is low and intake air can still be introduced. This will result in being damaged. Furthermore, because the adjustment range of the length of the intake passage is limited to some extent due to mechanical and spatial considerations, it is difficult to enhance the dynamic effect of intake air over a wide rotational speed range.

On the other hand, as a means for improving intake efficiency when the length and cross-sectional area of the intake passage are fixed, there is a method of adjusting the opening/closing timing of the intake valve, particularly the valve closing timing, depending on the operating state of the engine. When using this method, it is sufficient to control at least the closing timing of the intake valve according to the operating state of the engine so that the intake valve is closed when the pressure inside the cylinder and the pressure inside the intake passage immediately before the intake valve become equal. . However, in this case, due to the length and cross-sectional area of the intake passage, the synchronized state in which the positive pressure waves generated in the intake passage are utilized most effectively is limited to a specific operating range; In this region, the dynamic effect of the positive pressure wave is reduced. Therefore, there is a limit to the improvement in intake efficiency even by adjusting the opening/closing timing of the intake valve. Furthermore, it is mechanically difficult to adjust the opening/closing timing of the intake valve over a wide range.

(Objective of the Invention) In view of these circumstances, the present invention effectively utilizes the intake inertia effect over a wide range of engine operating ranges to improve intake efficiency, and improves output performance in various engine operating ranges compared to conventional methods. The present invention provides an engine intake system that can be significantly improved.

(Structure of the Invention) The present invention provides an intake passage length variable means that makes it possible to change the length of the intake passage, an intake passage cross-sectional area variable means that makes it possible to change the cross-sectional area of the intake passage, and an intake passage that at least closes the intake valve. The engine is equipped with a timing variable means that allows the timing to be changed, and a control device that controls the variable means in relation to each other depending on the operating state of the engine. In other words, by adjusting both the length and cross-sectional area of the intake passage according to the engine operating conditions, the intake inertia can be adjusted to a tuned state or a state close to this over a wide range of engine operating conditions, and the intake inertia can be adjusted accordingly. In addition, the intake timing is corrected to effectively utilize the intake inertia effect, thereby increasing intake efficiency.

Note that the cross-sectional area and length of the intake passage in this configuration refer to the cross-sectional area and length of the flow passage that substantially contributes to the intake inertia effect.

(Embodiment) FIGS. 1 and 2 show a first embodiment of the present invention. In these figures, 1 represents a plurality of cylinders 2
The engine body is composed of a cylinder block 3, a cylinder head 4, a cylinder head cover 5, etc. A piston 6 is inserted into each cylinder 2, and a combustion chamber 7 is formed above the piston 6. ing. Each combustion chamber 7 is equipped with a spark plug 8, and two intake ports 9, 10 and two exhaust ports 11, 12 formed in the cylinder head 4 are open. 9 to 12 are first and second intake valves 13 and 14 and first and second exhaust valves 1
5 and 16 to be opened and closed. Both intake ports 9 and 10 communicate with each other near the side end portion of the cylinder head 4, and a fuel injection valve 18 is installed in this communication portion 17.

The intake system for the engine body 1 includes an intake passage length variable means 20 and an intake passage cross-sectional area variable means 2.
1 are provided, and these are configured as follows. That is, both the intake ports 9, 1
Branch pipes 22 formed separately for each cylinder are connected to the communication portion 17 of 0, and these branch pipes 22 are integrally connected to a casing 23, and a cylindrical surge tank 24 is installed inside the casing 23. The surge tank 24
A spiral intake passage extension 25 is formed in the casing 23 around the periphery of the casing 23 . The intake passage extension 25 has a downstream end located on the upper outer side of the casing 23 that communicates with the branch pipe 22, and from this position wraps around the surge tank 24 to reach the upper inner side of the casing 23. A seal wall 26 whose upstream end touches the surge tank 24
is blocked off. A partition frame 27 provided in the casing 23 allows the intake passage extension 2 to
5 is divided into cylinders corresponding to the branch pipes 22. Further, air is introduced into the surge tank 24 from an air cleaner (not shown) via a throttle valve 28, and an opening 29 that opens into the intake passage extension 25 is provided in the peripheral wall of the surge tank 24. A rotating shaft 30 is connected to one end of this surge tank 24, and this rotating shaft 30 penetrates through the casing 23 and protrudes to the outside of the casing 23.
Motor 3 for driving the surge tank via 1 and 32
It is linked to 3. In this way, the motor 33
By rotating the surge tank 24, the substantial length of the intake passage from the opening 29 of the surge tank 24 to the combustion chamber side openings of the intake ports 9 and 10 can be changed steplessly. In addition, an intake passage length variable means 20 is configured.

Furthermore, the branch pipe 22 and the intake passage extension 2
5 is divided into a first intake passage 36 and a second intake passage 37 by a partition wall 35 provided therein, and the second intake passage 37 has an on-off valve 38.
is provided. This on-off valve 38 has a shaft 39,
It is opened and closed by an actuator 42 via a lever 40 and a rod 41.
In this way, the intake passage cross-sectional area variable means 21 is constructed, and according to this means, when the on-off valve 38 is closed, intake air is supplied to both the intake ports 9 and 10 only from the first intake passage 36, The cross-sectional area of one intake passage 36 becomes the substantial intake passage cross-sectional area, and when the on-off valve 38 is opened, both intake passages 3
Intake air is supplied from the intake passages 6 and 37, and the sum of the cross-sectional areas of both the intake passages 36 and 37 becomes the substantial cross-sectional area of the intake passage. Therefore, the cross-sectional area of the intake passage can be changed in two stages.

Further, as a valve operating mechanism for the intake and exhaust valves 13 to 16, camshafts 44 and 46 for intake valves and exhaust valves, which are rotationally driven by a crankshaft (not shown), are mounted on the cylinder head 4. are arranged, and cams 45, 47 are arranged on each cam shaft 44, 46. The exhaust valves 15 and 16 are opened and closed at a constant timing by a cam 47 via a tappet 48, and the first intake valve 13 is similarly opened and closed at a constant timing, but the second intake valve 14 is opened and closed at a constant timing. The timing of operation can be changed by a timing variable means 50. That is, the second intake valve 14 is equipped with a rotating member 51 that is rotatable about the camshaft 44, and a tapepet member 52 is held at the lower part of the rotating member 51. This tappet member 52 has a flat upper surface 52a that contacts the cam 45 provided on the camshaft 44, and a lower surface 52a that contacts the cam 45 provided on the camshaft 44.
2b is formed in an arcuate or spherical shape centered on the camshaft, and the upper end of the valve stem 14a of the second intake valve 14 is in contact with the lower surface 52b. Further, the upper end protrusion 5 of the rotating member 51
3 is penetrated by a control rod 54 parallel to the camshaft 44, with which a control lever 55 engages. This control lever 55 is connected to the control rod 5
The cylinder head cover 5 is slidable in a direction perpendicular to the axial direction of the cylinder head cover 5, and is actuated by an actuator 56 attached to a side wall of the cylinder head cover 5.

According to such means, the control lever 55 and the control rod 54 are controlled by the actuator 56.
When the rotating member 51 is rotated via the cam 45, the relative phase between the tappet member 52 and the cam 45 is changed, and the opening/closing timing of the second intake valve 14 is changed. That is, when the rotating member 51 is rotated in the same direction as the rotational direction X of the camshaft 44, the opening/closing timing is delayed, and when the rotating member 51 is rotated in the opposite direction, the opening/closing timing is advanced.

In the case of this timing variable means 50, the third
As shown in the figure, while the exhaust valves 15 and 16 and the first intake valve 13 are opened and closed at predetermined timings, the second intake valve 14 is opened and closed at the same timing as the first intake valve 13 and later than the first intake valve 13. By making the opening/closing timing changeable, the intake valve closing timing determined by the second intake valve 14 can be adjusted while the intake valve opening timing by the first intake valve 13 is kept constant. .

Reference numeral 60 denotes a control circuit (control device) for controlling each variable means 20, 21, 50, which inputs a detection signal from an engine rotation speed sensor 61 and sends a control signal to the motor 33 and each actuator 42, 56. is outputting. And this control circuit 6
0, the intake passage length variable means 20 and the intake passage cross-sectional area variable means 21 are controlled so as to obtain an intake inertia tuning state described later or a state similar thereto according to the engine speed, and in association with these. The timing variable means 50 is controlled so as to correct at least the closing timing of the intake valve to an optimal value. Specifically, as shown in FIG. 4, the intake passage length (line L), intake passage cross-sectional area (line S), and valve closing timing (line T) are controlled according to the engine speed. In other words, the intake passage length is the maximum length when the rotation speed is less than the set rotation speed Ra,
When the engine speed is higher than the set rotation speed Ra, it is gradually shortened as the engine speed increases, and the cross-sectional area of the intake passage is made smaller when the rotation speed is lower than the set rotation speed Ra, and increases when the rotation speed is higher than the set rotation speed Ra. There is. In addition, the valve closing timing is gradually delayed as the engine speed increases from the low speed side to around the set speed Ra above.
It is moved to the advance side by a predetermined value in the vicinity, and then is delayed as the engine speed increases further.

Next, the action of this intake device will be explained in Figures 5 and 6.
This will be explained using the characteristic diagram shown in the figure.

Figure 5 shows the fluctuation characteristics of the cylinder pressure at a specific engine speed, the negative pressure waves generated by the intake action in the intake inertia tuning state as defined later, and the reflections accompanying the negative pressure waves, with the horizontal axis as the crank angle. 2 shows the wave fluctuation characteristics and the combined pressure of the negative pressure wave and the reflected wave, that is, the fluctuation characteristics of the pressure immediately before the intake valve in the intake passage. As shown by curve A in this figure, the above cylinder internal pressure is IO at the time of intake valve opening.
The pressure gradually decreases from the later TDC point, reaches a peak during the downward movement of the piston, and then gradually increases, and becomes positive pressure after the BDC point. on the other hand,
The downward movement of the piston during the intake stroke generates a negative pressure wave shown by curve B in this figure just before the intake valve. The first reflected wave becomes a positive pressure wave as shown by curve C and returns to the cylinder side. Further, the second reflected wave returns as a negative pressure wave as shown by curve D. The pressure waves shown by these curves B, C, and D are combined to form the pressure immediately before the intake valve (curve E). As shown in this figure, the intake inertia tuning state due to the intake passage itself means that the waveform of the first reflected wave just before the intake valve is TDC
This is a state in which the first reflected wave begins to appear near the midpoint between and BDC and peaks at a specific point past BDC, and the intake inertia effect of the intake passage itself is maximized by this first reflected wave. In other words, it is a state in which the pressure just before the intake valve is maximized at the appropriate time after BDC, resulting in the optimum characteristics for the intake inertia effect. The pressure immediately before the intake valve shown by curve E becomes sufficiently larger than the cylinder internal pressure, so that a large amount of intake air can flow into the cylinder, and the intake inertia effect can be enhanced. If the timing at which the first reflected wave returns is delayed from the synchronized state, the pressure rise just before the intake valve will be delayed, and the pressure difference with the cylinder pressure near BDC will become smaller, resulting in a tendency for the suction efficiency to decrease. Furthermore, if the timing is earlier than the synchronized state, the peak value of the pressure immediately before the intake valve decreases due to the influence of the second reflected wave, so that the suction efficiency tends to decrease as well. In addition,
IC indicates the optimal closing timing of the intake valve, and this timing is after BDC, and is the time when the pressure just before the intake valve and the cylinder pressure almost match.

FIG. 6 shows the fluctuation characteristics of the cylinder internal pressure and the fluctuation characteristics of the pressure immediately before the intake valve at various engine speeds. In this figure, the curves A ₁ , A ₂ , and A ₃ indicated by broken lines indicate the fluctuation characteristics of the cylinder pressure at low speed, medium speed, and high speed, respectively, and thus the engine speed changes. As the number increases, the crankshaft rotation period is shortened, and the increase in cylinder pressure tends to be relatively delayed. Additionally, in this figure, the fluctuation characteristics of the pressure immediately before the intake valve when the intake inertia is in the synchronized state as described above is shown by a solid line curve E, and the intake passage is The fluctuation characteristics of the pressure just before the intake valve during low-speed rotation and high-speed rotation are shown by curves El and Eh, respectively, represented by two-dot chain lines, assuming that the cross-sectional area and length of are fixed. If the cross-sectional area and length of the intake passage are fixed in this way, the timing at which the first reflected wave returns to the cylinder side changes mainly depending on changes in engine speed, so the pressure immediately before the intake valve increases at high speeds. The rise in the intake valve is delayed, and the pressure immediately before the intake valve is attenuated early at low speed rotation.

Therefore, in the control circuit 60, the length and cross-sectional area of the intake passage are adjusted as indicated by the polygonal lines L and S in FIG. 4 in accordance with the engine speed. In other words, the timing at which the first reflected wave returns to the cylinder side is advanced by increasing the cross-sectional area of the intake passage, and also by shortening the length of the intake passage, so that in the rotation speed range above the set rotation speed Ra, The on-off valve 38 is opened to increase the cross-sectional area of the intake passage, and as the engine speed increases, the surge tank 24 is rotated in a direction to shorten the length of the intake passage. As a result, in the above rotation speed range, the intake inertia tuning state is maintained even if the engine speed changes. Furthermore, since adjustment in the direction of lengthening the intake passage length is mechanically restricted, the intake passage length is maintained at the maximum length in the low rotation speed range, but when the rotation speed is less than the set rotation speed Ra, the on-off valve 38 closes. By reducing the cross-sectional area of the intake passage, the fourth
The intake inertia tuning state is reached even at a low rotational speed indicated by the symbol Rb in the figure. In addition, even if the rotation speed is lower than the set rotation speed Ra, in the area above the low rotation speed Ra,
The length of the intake passage may be adjusted as shown by the two-dot chain line La in FIG.

In this way, the intake inertia effect is enhanced in various engine speed ranges. In particular, the variable range of the intake passage length and intake passage cross-sectional area is mechanically and spatially constrained, so adjusting only one of them will limit to some extent the rotational speed at which intake inertia can be synchronized. By adjusting both the passage length and the cross-sectional area of the intake passage, it is possible to tune the intake inertia over a wider rotational speed range, or to bring it closer to a tuned state.

In addition, in Fig. 6, IC ₂ indicates the optimal intake valve closing timing at medium speed rotation, and this timing is the timing when the cylinder pressure at medium speed rotation and the pressure immediately before the intake valve coincide (curve E and curve This corresponds to the time when A 2 intersects with A ₂ ), and if this is done, the suction efficiency at medium speed rotation will be maximized. However, if the timing is fixed at IC ₂ , even if the intake inertia is synchronized, the characteristics of the cylinder pressure will change depending on the engine speed as described above, so at high speeds, curve E and curve A will change. The intake valve is closed at a time when it is still possible to inhale due to pressure, before the time when ₃ intersects,
During low-speed rotation, the intake valve is closed after the cylinder pressure is high after the time when curve E and curve _A1 intersect, and therefore, when blowback in the intake system occurs.

Therefore, in the control circuit 60, each of the intake passage length and intake passage cross-sectional area variable means 20, 21
In addition to these controls, the timing variable means 50 is controlled in conjunction with these controls, thereby correcting the intake timing so as to obtain the maximum intake efficiency. In other words, by rotating the rotating member 51 by the actuator 56 that receives a signal from the control circuit 60, the pressure immediately before the intake valve and the cylinder internal pressure always match when the intake inertia is adjusted. The second intake valve 14 is closed at the point when the second intake valve 14 is closed, and therefore, during high speed rotation, the valve closing timing is delayed until the time point IC3 when the curve E and the curve _A3 intersect, and when the rotation speed is low, the closing timing is delayed until the time point _IC3 when the curve E and the curve _A1 almost intersect. The valve closing timing is advanced until the time point IC ₁ when . In this way, the intake efficiency can be maximized through the synergistic effect of adjusting the intake inertia by the intake passage and adjusting the valve closing timing.

In addition, with the cross-sectional area and length of the intake passage fixed, only the intake valve closing timing is determined at the point IC ₃ ' where curve Eh intersects with curve A ₃ during high-speed rotation, and at the intersection between curve El and curve A ₁ during low-speed rotation. Compared to the case where control is performed so that the timing IC ₁ ' is reached, by adjusting the intake inertia and adjusting the valve closing timing in relation to this, the pressure difference between the pressure just before the intake valve and the cylinder pressure before and after BDC can be reduced. Since this increases, the suction efficiency is greatly increased. Furthermore, when adjusting only the intake valve closing timing, it is necessary to adjust the valve closing timing over a relatively wide range according to fluctuations in engine speed, but it is possible to change the valve closing timing over a wide range. is mechanically very difficult. On the other hand, if the valve closing timing is adjusted after the intake inertia is synchronized, the valve closing timing adjustment amount can be reduced, which is mechanically advantageous.

Note that this improvement in intake efficiency is required mainly in high-load operating ranges, so the intake inertia is tuned according to the engine speed only when the engine load is above a predetermined value. In addition, the intake valve closing timing may be adjusted so that the intake inertia is not synchronized to reduce pumping loss during low load. In this case, in addition to the detection signal from the engine rotation speed sensor 61, the control circuit 60 may be provided with a detection signal from the load sensor 62, which is indicated by a two-dot chain line in FIGS. 1 and 2. .

7 and 8 show a second embodiment of the invention. In this embodiment, branch pipe 2 for each cylinder
A surge tank 24 is installed in a casing 23 in which 2 are connected.
is rotatably held, and the casing 2
This embodiment is similar to the first embodiment in that an intake passage extension portion 25 is formed in the third embodiment, and the intake passage length variable means 20 is configured so that the intake passage length can be changed by rotating the surge tank 24. However, the intake passage cross-sectional area variable means 71 is capable of continuously and steplessly changing the intake passage cross-sectional area by means of a movable wall 72. That is, from near the downstream end of the intake passage extension 25, the branch pipe 22 and the intake ports 9, 10 are connected.
A movable wall 72 is provided inside a portion extending to the vicinity of the combustion chamber side opening, and one end of this movable wall 72 is attached to the inner wall of the casing 23 via a rotatable small wall 73. An intermediate portion of the actuator 75 is connected to an actuator 75 via a rod 74. In this way, the movable wall 72 allows most of the intake passage for each cylinder 2 to be connected to the surge tank 2.
4 and a non-passage portion 77 that does not communicate with the surge tank 24,
By swinging the movable wall 72 by the actuator 75, the substantial cross-sectional area of the intake passage 76 is changed. A control signal is output from the control circuit 60 to the actuator 75. Valve closing timing variable means 5
The structure of 0, etc. is the same as in the first embodiment.

In this embodiment as well, the length and cross-sectional area of the intake passage are controlled in accordance with the engine speed so as to maintain the intake inertia in a synchronized state or a state approximating it. In this case, the range of variable intake passage length is limited due to engine mounting constraints, so
As shown by line _L1 in Figure 9, the intake passage length is controlled to be kept at the maximum length in the low rotation speed range below a predetermined rotation speed, and to be shortened as the engine speed increases above the predetermined rotation speed. , On the other hand, by controlling the intake passage cross-sectional area to increase as the engine speed increases in the low speed range, as shown by line _S1 , it is possible to appropriately adjust the intake inertia over a wide range. can. However, the method of adjustment is not limited to this example, and depending on the dimensions of the engine and intake system and output requirements, for example, the length of the intake passage may be adjusted in a relatively low rotation speed range as shown by line _L2 . At the same time, the cross-sectional area of the intake passage is adjusted in a relatively high rotation speed range as shown by line _S2 , or the cross-sectional area of the intake passage is adjusted over the entire rotation speed range as shown by line _S3 . It's okay. Intake efficiency is also affected by the intake flow rate, and this intake flow rate is related to the intake passage cross-sectional area, so the intake passage cross-sectional area and intake passage length should be adjusted so that the intake flow rate is adjusted to an optimal value and the intake inertia is synchronized. It will be more effective if these are controlled in relation to each other.

Also in this embodiment, in addition to adjusting the intake inertia, the closing timing of the intake valve is controlled in conjunction with this adjustment, thereby further increasing the intake efficiency.

10 and 11 show a third embodiment of the invention. In this embodiment, as the intake passage cross-sectional area variable means 81, a movable plate 82 is provided in the intake passage at a position close to the combustion chamber side opening of the intake port 9a to partially change the intake passage cross-sectional area. There is. One end of the movable plate 82 is rotatably attached to the inner surface of the side wall near the downstream end of the branch pipe 22, and the movable plate 82 is moved via a rod 84 by an actuator 83 that receives a control signal from the control rotation 60. The cross-sectional area of the intake passage near the downstream end of the intake passage is thereby adjusted. The structures of the intake passage length variable means 20, timing variable means 50, etc. are substantially the same as those in the first and second embodiments. In addition, in FIG. 11, the combustion chamber 7 of the cylinder 2 has an intake port 9a and an exhaust port 11a.
The figure shows a structure in which each intake valve 13a is opened one by one.In this case, a three-dimensional cam, etc., which will be described later, is used as the valve closing timing variable means instead of the structure shown in the figure, so that the opening timing can be adjusted for each intake valve 13a. It is also possible to delay the valve closing timing without delaying it.

In this embodiment, when the movable plate 82 is operated to adjust the cross-sectional area of the intake passage at a position close to the cylinder 2, the amplitude of the first reflected wave at the position immediately before the intake valve changes. Also the intake inertia effect can be adjusted. Therefore, by using this together with the intake passage length variable means 20, the intake inertia effect can be enhanced, and by controlling the valve closing timing, the intake efficiency can be further enhanced.

Note that the specific structure of the device of the present invention can be modified in various ways other than the above-mentioned embodiments. For example, as the timing variable means, a three-dimensional cam may be used to adjust the axial position, or a push rod type valve train may be used. It is also possible to employ a structure in which a valve operating adjustment member operated by hydraulic pressure or the like is interposed in the mechanism, or a phase difference adjustment means is incorporated into a belt transmission mechanism between the crankshaft and the camshaft. Further, in the above embodiment, 2
In a structure having two intake ports 9 and 10, the intake valve closing timing is shifted.
By using a three-dimensional cam or the like, the opening/closing timing of the intake valve and the amount of valve lift may be adjustable as shown in FIG.

(Effects of the Invention) As described above, the present invention adjusts the length and cross-sectional area of the intake passage so that the intake inertia is in a synchronized state or approaches it in accordance with the operating state of the engine, and in relation to this. Since at least the closing timing of the intake valve is adjusted to make maximum use of the intake inertia effect, it is possible to significantly increase intake efficiency in various engine operating ranges and improve output. Therefore, even if the variable ranges of the intake passage length, intake passage cross-sectional area, and at least the closing timing of the intake valve are mechanically and spatially limited, synergistic effects can be achieved by adjusting these three. , it is possible to improve output over an extremely wide range of engine operation.

[Brief explanation of the drawing]

FIG. 1 is a vertical sectional view showing a first embodiment of the device of the present invention, FIG. 2 is a sectional view taken along the - line in FIG. Fig. 4 is an explanatory diagram showing examples of adjusting the intake passage length, intake passage cross-sectional area, and valve closing timing according to the engine speed, and Fig. 5 is a characteristic diagram of the cylinder pressure and various pressure waves immediately before the intake valve. FIG. 6 is a characteristic diagram of the cylinder pressure and the pressure immediately before the intake valve in various engine speed ranges, FIG. 7 is a vertical sectional view showing the second embodiment of the device of the present invention, and FIG. 9 is an explanatory diagram showing an example of adjusting the intake passage length and cross-sectional area of the intake passage according to the second embodiment, and FIG. 10 is a third embodiment of the device of the present invention. 11 is a partial sectional view taken along the line XI-XI in FIG. 10, and FIG.
The figure is an explanatory diagram showing another example of the opening/closing timing of the intake and exhaust valves. 1... Engine body, 9, 10, 9a... Intake port, 13, 14, 13a... Intake valve, 20...
...Intake passage length variable means, 21, 71, 81... Intake passage cross-sectional area variable means, 50... Timing variable means, 60... Control circuit.

Claims (1)

[Claims] 1. Intake passage length variable means that allows the length of the intake passage to be changed; intake passage cross-sectional area variable means that allows the cross-sectional area of the intake passage to be changed; and timing variable means that allows at least the closing timing of the intake valve to be changed. What is claimed is: 1. An intake system for an engine, characterized in that it is provided with: and a control device that controls the variable means in relation to each other according to the operating state of the engine.