JPH0639898B2 - Engine intake system - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an intake device for an engine, and more particularly to a device for improving output by utilizing an intake inertia effect.

(Prior Art) Conventionally, in the intake system of an engine, in order to improve the output by the so-called intake inertia effect using the positive pressure wave reflected at the open end of the intake passage and returned to the cylinder during the intake stroke, As shown in Japanese Patent Laid-Open No. 58-20331, it is known that the intake passage for each cylinder of the engine is formed to have a predetermined length and cross-sectional area suitable for having an intake inertia effect. In this case, the intake inertia effect is maximized in a specific operating region determined by the length and cross-sectional area of the intake passage, for example, a specific engine speed, and therefore the output is increased near this speed, but the output torque is increased in other speed regions. Is reduced, and especially on the rotation speed side higher than the inertia tuning speed, both the effect of the intake inertia effect decreases and the intake time becomes shorter due to the increase in the rotation speed.
The output torque tends to drop significantly as the rotation speed increases, and measures against this have been desired.

(Object of the Invention) In view of such a situation, the present invention enhances the intake efficiency by adjusting at least the closing timing of the intake valve in addition to the intake inertia effect by the intake passage itself, and particularly the timing variable means with a limited variable range. It is intended to provide an intake device for an engine, which can effectively improve the output and sufficiently improve the output in an operating region on the high engine speed side where there is a strong demand for output improvement.

(Structure of the Invention) The present invention relates to an intake device for an engine, which is provided with an intake passage whose length and cross-sectional area are set so that the engine torque peaks due to the intake inertia effect at a predetermined engine speed. At least the timing varying means for changing the valve closing timing, the valve closing timing is made constant in the region on the low rotation side up to the predetermined rotation speed, and as the engine rotation speed increases in the region above the predetermined engine rotation speed. And a control device for controlling the timing varying means so as to delay the valve closing timing. In other words, the length and cross-sectional area of the intake passage with respect to the cylinder of the engine are determined so that the intake inertia is synchronized at an appropriate engine speed, and at least the closing timing of the intake valve in the operating region higher than this is determined. The adjustment is configured to suppress the decrease in output torque.

(Embodiment) FIGS. 1 and 2 show a first embodiment of the present invention. In these figures, reference numeral 1 denotes an engine body having a plurality of cylinders 2, which is composed of a cylinder block 3, a cylinder head 4, a cylinder head cover 5, and the like.
A piston 6 is inserted into each cylinder 2 and a combustion chamber 7 is formed above the piston 6. Each combustion chamber 7 is equipped with a spark plug 8 and two intake ports 9 and 10 formed in the cylinder head 4 are provided.
And exhaust ports 11 and 12 are opened so that these ports 9 to 12 are opened and closed by the first and second intake valves 13 and 14 and the first and second exhaust valves 15 and 16. Has become. The intake ports 9 and 10 communicate with each other in the vicinity of the side end of the cylinder head 4, and the communication part 17 is equipped with a fuel injection valve 18. In addition, from the surge tank 21 to each cylinder 2
A branch pipe 22 which is branched separately is connected to the surge tank 21 from an air cleaner (not shown) to the throttle valve 2
The air is introduced through 3. In this way, the cylinder-by-cylinder intake passage is constituted by the portion extending from the branch pipe 22 to the intake ports 9 and 10, and the length and cross-sectional area of this intake passage have an intake inertia effect in a specific engine speed region according to demand. It is set to be raised.

Further, as a valve mechanism for the intake and exhaust valves 13 to 16, each of the intake valve and exhaust valve camshafts 2 which are rotationally driven by a crankshaft (not shown) is mounted on the cylinder head 4.
4 and 26 are arranged, and the cam 2 is attached to each cam shaft 24 and 26.
5, 27 are provided. Then, the exhaust valves 15 and 16
Is opened and closed at a constant timing by the cam 27 via the tappet 28, and similarly the first intake valve 13 is also opened and closed at a constant timing, but the second intake valve 14 is operated by the timing varying means 30 as described below. The timing of can be changed. That is, for the second intake valve 14,
A rotating member 31 rotatable about the cam shaft 24 is provided, and a tappet member 32 is held below the rotating member 31. The tappet member 32 has a flat upper surface 32a that comes into contact with the cam 25 provided on the cam shaft 24.
The lower surface 32b is formed in an arc surface or a spherical surface centered on the cam shaft, and the upper surface of the valve stem 14a of the second intake valve 14 is in contact with the lower surface 32b. Further, a control rod 34 parallel to the cam shaft 24 penetrates through the upper end protruding portion 33 of the rotating member 31, and a control lever 35 is engaged with the control rod 34. This control lever 35
Is slidable in a direction orthogonal to the axial direction of the control rod 34 and is operated by an actuator 36 attached to the side wall of the cylinder head cover 5.

According to such means, when the rotating member 31 is rotated by the actuator 36 via the control lever 35 and the control rod 34, the relative phase between the tappet member 32 and the cam 25 is changed accordingly. Thus, the opening / closing timing of the second intake valve 14 is changed. That is, when the rotating member 31 is rotated in the same direction as the rotation direction X of the cam shaft 24, the opening / closing timing is delayed, and when the rotating member 31 is rotated in the opposite direction, the opening / closing timing is advanced.

When the timing varying means 30 is used, as shown in FIG. 3, the exhaust valves 15 and 16 and the first intake valve 13 are opened and closed at predetermined timings, while the second intake valve 14 is the first intake valve. Since the opening / closing timing can be changed from the same timing as 13 to the later timing, the intake valve closing timing determined by the second intake valve 14 is maintained while the intake valve opening timing by the first intake valve 13 is kept constant. The timing will be adjusted. Then, the timing varying means 30 is designed in advance so that when the valve closing timing is most advanced within such a variable range, the valve closing timing becomes the optimum valve closing timing at the intake inertia tuning rotational speed R ₀ described later.

Reference numeral 40 denotes a control circuit (control device) for controlling the timing varying means 30, which inputs a detection signal from the engine speed sensor 41 and outputs a control signal to the actuator 36. By this control circuit 40, as shown in FIG. 5, it is lower than the intake inertia tuning speed R ₀ based on the relationship between the engine speed and the indicated mean effective pressure Pi shown in FIG. In the engine speed region, the intake valve closing timing is kept constant in the most advanced state, and at the intake inertia tuning speed R ₀ or higher, the timing varying means 30 is controlled so as to delay the valve closing timing as the engine speed increases. There is.

Since it is mainly required to improve the output in a high load operation range, the above-described control of the intake valve closing timing may be performed only when the engine load is a predetermined value or more. In this case, in addition to the detection signal from the engine speed sensor 41, the control circuit 40 may be supplied with the detection signal from the load sensor 42 shown by the two-dot chain line in FIG.

The operation of this intake device will be described below.

First, the intake inertia effect will be explained. When the piston starts descending during the intake stroke, negative pressure is generated in the cylinder and a negative pressure wave is generated immediately before the intake valve. This negative pressure wave propagates in the intake passage, Upstream open end (surge tank 2
At the open end to 1), the positive and negative are inverted and reflected, so that the first reflected wave becomes a positive pressure wave and returns to the cylinder side during the intake stroke period. If this first reflected wave is returned at an appropriate time in the latter half of the intake stroke, the pressure immediately before the intake valve becomes sufficiently higher than the cylinder internal pressure until the time after BDC (piston bottom dead center). Efficiency is improved. Such an effect is called an intake inertia effect. Further, the intake inertia tuning speed is an engine speed at which the intake inertia effect of the intake passage itself is maximized by returning the first reflected wave at the optimum time. Depends on length and cross section,
In the rotation speed region other than this, the timing at which the first reflected wave is returned is deviated, so that the intake inertia effect is reduced. The intake inertia effect affects the output torque.

The output torque is also affected by the closing timing of the intake valve. That is, while the pressure immediately before the intake valve is higher than the pressure in the cylinder, it is possible to inhale into the cylinder, and if the intake valve is open until the time when the pressure in the cylinder becomes higher than the pressure immediately before the intake valve, blowback occurs, It is optimal for intake efficiency to close the intake valve at the time when the pressure immediately before the intake valve and the pressure in the cylinder substantially match, and the output torque is increased. Then, for example, when the valve closing timing has to have been fixed so that the optimum intake inertia tuning rotational speed R _0, as shown by the broken line A in FIG. 4, the output torque in the intake inertia tuning rotational speed R ₀ (Indicated by the indicated mean effective pressure Pi of the cylinder in this figure) is maximum, but for example, on the lower rotation side or the higher rotation side, the intake inertia tuning rotational speed R ₀
As the distance from the engine decreases, the output torque decreases due to a decrease in the intake inertia effect, and the decrease in the output torque tends to increase due to the effect that the intake time becomes shorter especially on the high rotation side.

Therefore, in order to satisfy the demand for output improvement especially in the high rotation region of the intake inertia tuning rotation speed R ₀ or more, the control circuit 4 is provided.
With 0, the timing changing means 30 is controlled so as to change the valve closing timing in accordance with the fluctuation of the engine speed in this high engine speed range. That is, as the engine speed increases, the optimum valve closing timing shifts to the lag side, and accordingly, the valve closing timing is changed in the high engine speed region as shown in FIG. As a result, as shown by the solid line B in FIG. 4, the output torque can be improved in the high rotation speed range.

In this case, the reason why the valve closing timing is kept constant in the rotational speed range lower than the intake inertia tuning rotational speed R ₀ is that the valve timing is closed over a wide range corresponding to the entire operating region of the engine due to the mechanism of the timing varying means 30. This is because it is difficult to change the timing. That is, under the constraint that the variable range of the timing varying means 30 is mechanically limited, when the valve closing timing is to be changed in a partial rotation region, the valve closing timing is advanced on the low rotation side. Rather than doing so, delaying the valve closing timing on the high rotation side is advantageous in improving output because the suction time can be secured. Even under such conditions, the length and cross-sectional area of the intake passage and at least the variable range of the valve closing timing of the intake valve are set in accordance with the rotational speed region in which the output is required, so that the output is properly output. Will be improved.

When a high output is required in a relatively low engine speed range, the above-described embodiment is performed with the cross-sectional area and length of the intake passage set so that the intake inertia tuning speed is lowered accordingly. Similarly, the valve closing timing may be controlled.

In addition to the structure shown in the figure, as the timing varying means, for example, a three-dimensional cam can be used to adjust its axial position, and a push rod type valve actuating mechanism is provided with a valve actuating member operated by hydraulic pressure or the like. Alternatively, a structure in which the phase difference adjusting means is incorporated in the belt transmission mechanism between the crank shaft and the cam shaft can be adopted. When a three-dimensional cam or the like is used, the opening / closing timing of the intake valve and the valve lift amount may be adjustable as shown in FIG.

(Effects of the Invention) As described above, according to the present invention, the length and cross-sectional area of the intake passage are set so as to enhance the intake inertia effect in the specific engine operating region, and the engine torque peaks due to the intake inertia effect. In the operating range higher than the predetermined speed, the valve closing timing is delayed as the engine speed increases, so the intake inertia effect is reduced and the intake time is shortened. In an operating region where the engine output tends to greatly decrease as the temperature rises, the output reduction tendency can be suppressed. Therefore, the output can be improved over a wide operating range by maximally utilizing the valve closing timing variable range which is mechanically limited.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing an embodiment of the device of the present invention, FIG. 2 is a sectional view taken along line II-II of FIG. 1, and FIG. 3 is an explanatory view showing opening and closing timings of intake and exhaust valves, FIG. 4 is an explanatory view showing the relationship between the engine speed and the indicated mean effective pressure of the cylinder, FIG. 5 is an explanatory view showing an example of control of the intake valve closing timing according to the engine speed, and FIG. FIG. 6 is an explanatory diagram showing another example of opening / closing timings of exhaust valves. 1 ... Engine body, 9, 10 ... Intake port, 13,
14 ... Intake valve, 22 ... Branch pipe, 30 ... Timing changing means, 40 ... Control circuit.

Claims (1)

[Claims] 1. An engine intake system having an intake passage whose length and cross-sectional area are set so that the engine torque reaches a peak due to an intake inertia effect at a predetermined engine speed. And a variable timing means that makes it possible to change the valve closing timing in a low rotation speed region up to the predetermined rotation speed, and the valve closing timing is set as the engine rotation speed increases in a region of the predetermined engine rotation speed or more. An intake system for an engine, comprising: a control device for controlling the timing varying means so as to delay the operation.