JPS61250338A - Suction device for engine - Google Patents

Abstract

PURPOSE:To prevent combustion gas inside a combustion chamber from flowing back to the inside of a suction passage, by opening this suction passage at that point that pressure at the upstream side of a timing valve, namely, suction pressure in the suction passage and pressure at the downstream side of the timing valve, namely, pressure in the combustion chamber are equalized. CONSTITUTION:A timing valve 18 is rotatably installed in a branch passage branched off from a surge tank 14 via a bearing 19. And, the timing valve 18 is connected to a timing pulley 22 via a timing advance regulating mechanism 21, and this regulating mechanism 21 is made so as to move its arm 38 in an axial direction 37 by a controlling device on the basis of each signal out of each of sensors 17, 46 and 47 detecting an engine running state. At this time, the suction passage 14 is opened by the timing valve 18 at that point that pressure P2 at the upstream side of the timing valve 18, namely suction pressure in the suction passage 14 becomes equal to pressure P1 at the downstream side of the timing valve 18, namely, pressure in a combistion chamber 11.

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention relates to an intake system for a four-stroke engine that prevents backflow of combustion gas into the intake passage at low loads and improves combustibility, etc. It is.

(Prior Art) Conventionally, in a 4-cycle engine, as shown in Fig. 3,
The opening periods of the intake valve 12 and the exhaust valve 13 overlap. This overlap OL inevitably occurs as a result of lengthening the opening time of the intake valve 12 in order to improve filling efficiency under high loads.

However, because of the overlap OL, that is, the intake valve 12 opens at the end of the exhaust stroke, when the pressure in the intake passage is low (the negative pressure is large) and the load is low, the combustion gas in the combustion chamber flows into the intake passage. flow back to. When such a backflow occurs, two things occur: the backflowing combustion gas is sucked into the combustion chamber together with intake air again, and the pressure inside the combustion chamber decreases due to the backflow, making it impossible to exhaust gas sufficiently. As a result, combustion gas remains in the combustion chamber, reducing combustibility.

In order to deal with this problem, a main intake valve with no overlap is provided in the main intake passage, while a auxiliary intake valve with overlap and a rotary valve are provided in the auxiliary intake passage.
There is a known technique that attempts to prevent the backflow of combustion gas by closing the rotary valve and allowing air to be taken in only from the main intake valve during low load conditions where backflow of combustion gas is likely to occur (Utility Model Application No. 56-142226). However, in this conventional technology, since the timing at which the auxiliary intake valve opens is constant, the timing at which intake starts from the auxiliary intake passage is constant and cannot be changed depending on the load, so it is difficult to prevent the above-mentioned backflow. cannot be achieved effectively.

(Object of the Invention) This invention was made to eliminate the above-mentioned conventional drawbacks, and by opening the intake passage when the pressure in the combustion chamber and the negative pressure in the intake passage become equal, The main purpose is to prevent combustion gas from flowing back into the intake passage and improve combustibility.

(Structure of the Invention) In order to achieve the above object, the present invention provides a timing valve in the intake passage, and at least when the load is low, the timing is set at a crank angle such that the pressures on the upstream side and the downstream side of the timing valve in the intake passage match. The structure includes a control means for opening the valve.

As a result, the intake passage is opened when the pressure on the upstream side of the timing valve, that is, the negative pressure in the intake passage, and the pressure on the downstream side of the timing valve, that is, the pressure in the combustion chamber, become equal. Combustion gas is prevented from flowing back into the intake passage. Furthermore, since the opening of the intake passage is delayed, the work required to overcome the negative pressure in the intake passage and draw intake air into the combustion chamber, that is, pumping loss, is reduced.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 1, 10 is a four-stroke engine with multiple cylinders, and an intake valve 12 and an exhaust valve 13 are provided above a combustion chamber 11 of each cylinder. The ports of the exhaust passage 15 are opened and closed by the exhaust valve 13, respectively. The intake passage 14 is a main passage 14a.

Consisting of a surge tank 14b and a branch passage 14c branching from the surge tank 14b, a throttle valve 17 is provided in the main passage 14a, and a timing valve 18 consisting of a rotary valve is provided in the first branch passage 14c via a bearing 19. It is rotatably provided.

The timing valve 18 opens and closes the branch passage 14c, and is connected to a timing pulley 22 via an advance adjustment mechanism 21, which will be described later.
This timing pulley 22 is connected to an output pulley 25 of a crankshaft 24 by a toothed belt 23, and rotates at the same rotational speed of the crankshaft 24.

The advance angle adjustment mechanism 21 shown in FIG. A helical spline 34 having a twist in the opposite direction to the helical spline 32 is provided at 33, and a connecting pipe 35 is engaged with both the helical splines 32 and 34 to connect the valve shaft 31 and the rotating shaft 33, thereby forming an arm. 38 connects the connecting pipe 35
is moved in the axial direction 37. By this movement, the valve shaft 31 is rotated relative to the rotating shaft 33 in a certain direction, and the opening timing of the timing valve 18 is adjusted relative to the crank angle, that is, relative to the opening timing of the intake valve 12. advance and retreat.

As shown in FIG. 3, the opening timing of the intake valve 12 is 4.
2 is set before the top dead center TDC, and the closing timing 43 of the exhaust valve 13 is set after the top dead center TDC. Therefore, the opening timing of the intake valve 12 is 4.
2 is before the closing timing 43 of the exhaust valve 13,
Overlap O in the opening period of the intake valve 12 and exhaust valve 13
L occurs.

In FIG. 1, 45 is a control means, and the throttle valve 17
The throttle opening signal a from the engine, the rotational speed signal from the engine rotational speed sensor 47, and the pressure signal C from the pressure sensor 46 provided in the surge tank 12b are input, and the advance angle signal d is output. The arm 38 of the advance angle adjustment mechanism 21
is moved in the axial direction 37, and the opening timing 41 of the timing valve 18 shown in FIG. 3 is moved forward or backward relative to the opening timing 42 of the intake valve 12.

Next, advance control of the timing valve 18 by the control means 45 will be explained.

First, the timing valve 18 in the intake passage 14 in FIG.
The pressure P1 on the downstream side of the engine is approximately determined by the engine speed, engine load, and crank angle. Therefore, the pressure P1 is mapped and stored in the control means 45. The pressure P1 is equal to the pressure in the combustion chamber 11, and as shown in FIG. Therefore it decreases. The crank angle CD at which this pressure Pi is equal to the pressure indicated by the pressure signal C from the pressure sensor 46, that is, the pressure P2 on the upstream side of the timing valve 18, is determined.
1, the arm 38 of the advance adjustment mechanism 21 is moved in the axial direction 37, and the timing valve 18 is rotated relative to the rotating shaft 33. At this time, the lower the engine load, the lower the pressure P2 on the upstream side of the timing valve 18.
The opening timing 41 of No. 8 moves backward (moves to the right in FIG. 3).

In this way, the pressure P2 on the upstream side of the timing valve 18. In other words, when the negative pressure in the intake passage 14 becomes equal to the pressure Pl on the downstream side of the timing valve 18, that is, the pressure in the combustion chamber 11, the intake passage 14 is opened by the timing valve 18. Even though there is an overlap OL during the opening period of the exhaust valve 13, combustion gas is prevented from flowing back from the combustion chamber 11 to the intake passage 14. Therefore, exhaust is performed smoothly, no combustion gas remains in the combustion chamber, and combustibility is improved.

The timing valve 18 is controlled by the control means 45 only when the load of the engine 10 is low. In other words, when the advance signal d is not output, the opening timing 41 of the timing valve 18 is the same as that of the intake valve 12. coincides with the opening timing 42 of
The opening timing 41 of the timing valve 18 is advanced in the manner described above.

When the level of the advance angle signal d is equal to or higher than a predetermined value.

That is, under conditions other than low load, the opening timing 41 of the timing valve 18 is the opening timing 4 of the intake valve 12 as described above.
2, the intake passage 14 is opened at the opening timing 42 of the intake valve 12. This lengthens the open period of the intake passage 14 and improves the filling efficiency.

It goes without saying that the advance angle signal d may be output in all load ranges to change the opening timing 41 of the timing valve 18.

Next, the reason why the pumping loss of the engine 10 is reduced by the present invention will be explained.

First, the four-stroke engine 10 has suction, compression, explosion, expansion, and exhaust strokes, as shown in the PV diagram in FIG. This corresponds to the work required to overcome the negative pressure P2 in the intake passage and draw intake air into the combustion chamber, that is, pumping loss.

In a normal four-stroke engine that does not have the timing valve 18, as clearly shown in FIG. 5, the engine moves from the exhaust stroke to the intake stroke by following a vertical path (V=constant) shown by a broken line. On the other hand, in the engine 10 of the present invention, the timing valve 18 shown in FIG. 14 is opened, the engine moves from the exhaust stroke in FIG. 5 to the intake stroke by following the diagonal path shown by the solid line. Therefore, the pumping loss is reduced by the area indicated by the mesh hatching. As a result, the thermal efficiency of the engine is improved.

(Effects of the Invention) As explained above, according to the present invention, the pressure on the upstream side of the timing valve, that is, the negative pressure in the intake passage, and the pressure on the downstream side of the timing valve, that is, the pressure in the combustion chamber, are equal. Since the intake passage is opened at the time when the combustion chamber reaches the maximum temperature, combustion gas in the combustion chamber is prevented from flowing back into the intake passage, and as a result, no combustion gas remains in the combustion chamber, improving combustibility.

Furthermore, since the opening of the intake passage is delayed, the work required to overcome the negative pressure in the intake passage and draw intake air into the combustion chamber, that is, the pumping loss, is reduced, and the thermal efficiency of the engine is improved accordingly.

[Brief explanation of the drawing]

Fig. 1 is a schematic plan view showing one embodiment of the present invention, Fig. 2 is a schematic side view showing the main parts of Fig. 1, and Fig. 3 is the opening/closing timing of the intake valve and exhaust valve and the pressure in the intake passage FIG. 4 is a PV diagram of the engine, and FIG. 5 is a PV diagram showing the fourth main part. DESCRIPTION OF SYMBOLS 10... Engine, 11... Combustion chamber, 12... Intake valve, 13... Exhaust valve, 14... Intake passage, 18...
...Timing valve, 45...Control means. Figure 1. 13: Exhaust valve Figure 2 Figure 3 Crank angle Combustion chamber volume @V

Claims (1)

[Claims] (1) In an engine intake system in which the opening timing of the intake valve is set before the closing timing of the exhaust valve, the timing valve provided in the intake passage and the upstream side of the timing valve in the intake passage at least under low load and control means for opening a timing valve at a crank angle at which downstream pressures match.