JPH0543202Y2 - - Google Patents

Description

[Detailed explanation of the idea] (Industrial application field) The present invention relates to a valve device for an internal combustion engine.

(Prior art) In the case of internal combustion engines for automobiles, multiple exhaust valves and intake valves provided in one cylinder are operated independently of each other for the purpose of improving combustibility in high-speed, high-load ranges. is proposed.

As this type of valve device, for example,
What was disclosed in Publication No. 17967 is the valve timing of two exhaust valves in the same cylinder in a 4-stroke, 4-valve internal combustion engine, as shown in Figure 5.
Valve timing of E ₁ , E ₂ and two intake valves
I ₁ and I ₂ each have a predetermined phase difference, and near top dead center from the exhaust stroke to the intake stroke, one set of exhaust valves and intake valves closes and the other set of exhaust valves and intake valves opens. This increases the flow rate of fresh air in the cylinder to improve scavenging efficiency. In addition, only one intake valve opens near the bottom dead center from the intake stroke to the compression stroke, creating an intake swirl in the cylinder.
It is designed to improve combustibility mainly in high-speed, high-load ranges.

(Problem to be solved by the invention) By the way, in such a valve device, since the two exhaust valves have a phase difference in the timing of full closing, valve overlap occurs when the intake and exhaust valves open at the same time. When the actual valve opening area of the exhaust valve becomes smaller,
In order to obtain sufficient intake inertia supercharging effect in the high-speed, high-load range, it was necessary to lengthen the valve overlap period.However, if the valve overlap period is made long, in the low-speed, low-load range, Even with a small valve opening area, the exhaust gas flows back into the cylinder from downstream of the exhaust valve due to the large suction negative pressure, so the proportion of residual gas increases in the low speed and low load range, where not much fuel is supplied to begin with, resulting in combustion. There was a problem in that it greatly damaged the sex.

The purpose of the present invention is to solve these conventional problems and improve performance in the entire engine speed range.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a valve device for an internal combustion engine that includes a plurality of exhaust valves in one cylinder, in which the valve diameters of the plurality of exhaust valves are made to be different, In addition, the opening operation of the exhaust valve with a smaller diameter is delayed than that of the exhaust valve with a larger diameter, and the closing timing of each exhaust valve is configured to be synchronized with each other.

(Function) Pressure waves are generated in the exhaust passage as the exhaust valve opens, and scavenging is promoted in the rotation speed range where the immediate downstream side of the exhaust valve becomes negative pressure when the exhaust valve is fully closed. In the rotation speed range where the engine pressure is high, the pumping loss used to discharge exhaust gas increases, and the torque generated by the engine decreases, resulting in a so-called torque valley in this rotation speed range.

This invention is designed to reduce the blowdown pressure that is applied when a small-diameter exhaust valve opens because the diameters of the exhaust valves in the same cylinder are different, and the opening area of each cylinder is different even with the same lift when the valve is opened. is smaller than a large diameter exhaust valve.

Furthermore, because the small-diameter exhaust valve is configured to open later than the large-diameter exhaust valve, the blowdown pressure that is input when the small-diameter exhaust valve opens is equal to the blowdown pressure that is input when the large-diameter exhaust valve opens. They have a phase difference with each other that lags behind.

In this way, the blowdown pressures that enter the exhaust passage as the large and small exhaust valves open are combined with a phase difference, and in addition, the exhaust valve opening area increases sequentially at the beginning of the exhaust stroke. Therefore, the pressure pulsations in the exhaust passage become smaller accordingly. As a result, pumping loss in the rotation speed range where the pressure immediately downstream of the exhaust valve is positive when the exhaust valve is fully closed is reduced.
The exhaust inertia effect promotes scavenging, reduces residual gas, and increases volumetric efficiency, which reduces torque drop in this rotational speed range.

In addition, by synchronizing the closing timings of multiple exhaust valves in the same cylinder, the effective opening area of the exhaust passage that each exhaust valve opens when valves overlap becomes larger. It is no longer necessary to set the overlap timing so large, and as a result, it is possible to reduce backflow of exhaust gas in the low load range, improve combustibility, and ensure idle stability.

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

As shown in FIGS. 1A and B, in a 4-cycle, 4-valve internal combustion engine, the valve diameters d ₁ and d 2 of the two exhaust valves 1 and ₂ provided in the same cylinder are made to differ by a predetermined ratio, and , correspondingly each exhaust board 3,
4 are also formed with different diameters. In addition, 5 in the figure
is a cylinder head, and 6 and 7 are intake valves.

Curve E ₁ shown in FIG. 2 shows the valve timing of exhaust valve 1, E ₂ shows the valve timing of exhaust valve 2, and I shows the valve timing of intake valves 6 and 7, respectively. The small-diameter exhaust valve 2 begins to open with a delay of phase difference θ from the large-diameter exhaust valve 1 just before the bottom dead center, which begins the exhaust stroke, reaches its maximum lift point in the middle of the exhaust stroke, and reaches the top dead center, which begins the intake stroke. After passing the point, they fully close in synchronization with each other. The exhaust valves 1, 2 and the intake valves 6, 7 are provided with a predetermined valve overlap with the top dead center in between.

It is constructed as described above, and its operation will be explained next.

Due to the different valve diameters of exhaust valves 1 and 2 in the same cylinder, the opening area of each is different even with the same lift when the valve is opened, so the blowdown pressure that is input when the small diameter exhaust valve 2 is opened is It is smaller than the large diameter exhaust valve 1.

Furthermore, since the small-diameter exhaust valve 2 is configured to open later than the large-diameter exhaust valve 1, the blowdown pressure that is incident when the small-diameter exhaust valve 2 opens is not incident when the large-diameter exhaust valve 1 opens. It lags behind the blowdown pressure and has a phase difference with each other.

In Fig. 3, the pressure waves generated in the exhaust passages downstream of the exhaust valves 1 and 2 are shown by broken lines, and the blowdown pressure (dotted chain line) that is incident when the exhaust valve 1 opens
On the other hand, the blowdown pressure (double-dashed line) that is incident when the exhaust valve 2 opens is delayed by a certain phase difference, so the amplitude of the pressure wave (dashed line) created by combining these is equal to that of the two exhaust gases. This can be kept smaller than in the case of a conventional device in which the valves open in the same phase (solid line).

Figure 4 shows the results of actually measuring pressure fluctuations under operating conditions at a rotational speed of 3600 rpm, where the pressure wave generated 120 mm downstream of exhaust valves 1 and 2 becomes positive pressure when exhaust valves 1 and 2 are fully closed. The characteristic shown by the broken line and the solid line in the figure shows the case of a conventional device in which two exhaust valves open in the same phase. As can be seen from this experimental result, in this example, blowdown (A in the figure)
The amplitude of the reflected wave (section B in the figure) is also suppressed to a small extent as the amplitude of the reflected wave (section B in the figure) decreases.

As mentioned above, around 3600rpm, exhaust valves 1 and 2
When the exhaust valves 1 and 2 are fully closed, the pressure immediately downstream of the exhaust valves 1 and 2 becomes positive, resulting in a torque valley, but in this embodiment, the blowdown pressure that is input when the exhaust valves 1 and 2 are opened is mutually Due to the phase difference, the amplitude of the pressure wave generated in the exhaust passage becomes smaller, which reduces the pumping loss used to discharge exhaust gas, reduces residual gas, and increases the volumetric efficiency of intake air. It is possible to reduce the drop in torque in several ranges.

In addition, by completely closing the exhaust valves 1 and 2 in synchronization with each other, the actual opening area of the exhaust passage that each exhaust valve 1 and 2 opens when there is valve overlap with the intake valves 3 and 4 increases. There is no need to set the valve overlap period so large. As a result, while volumetric efficiency is ensured by utilizing the inertia of the intake air in the high-speed, high-load range, exhaust gas flows into the cylinder from downstream of the exhaust valves 1 and 2 due to the large suction negative pressure in the low-speed and low-load range. This suppresses backflow and prevents deterioration of combustibility due to residual gas, improving idle stability, etc.

(Effects of the invention) As described above, according to the invention, a plurality of exhaust valves provided in the same cylinder have different valve diameters, and the small-diameter exhaust valve opens later than the large-diameter exhaust valve. , the relatively low blowdown pressure from the small-diameter exhaust valve is made to enter the exhaust passage with a phase difference with respect to the blowdown pressure from the large-diameter exhaust valve, and the exhaust valve at the beginning of the exhaust stroke is We tried to suppress the rapid increase in opening area, so
By sufficiently weakening the pressure waves generated in the exhaust passage, it is possible to reduce pumping loss in the rotation speed range where torque troughs occur, thereby improving the output of the engine.

In addition, in this invention, the closing timings of the large and small exhaust valves are synchronized with each other, so it is no longer necessary to set the valve overlap period so large in response to high speed and high load ranges. This also has the effect of suppressing the backflow of exhaust gas into the cylinder, thereby improving combustibility and idling stability.

[Brief explanation of the drawing]

Fig. 1A is a sectional view of an engine showing an embodiment of the present invention, Fig. 1B is a plan view of the cylinder head, Fig. 2 is an explanatory diagram of the operation of the intake and exhaust valves, and Fig. 3 shows the operation. Diagram, FIG. 4 is a diagram showing the experimental results. FIG. 5 is an explanatory diagram of the operation of an intake and exhaust valve showing a conventional example. 1, 2... Exhaust valve, 3, 4... Exhaust port, 5
...Cylinder head, 6,7...Intake valve.

Claims (1)

[Scope of utility model registration request] An exhaust system for an internal combustion engine, comprising a plurality of exhaust valves in one cylinder, the plurality of exhaust valves having different valve diameters, the opening operation of the exhaust valves having a smaller valve diameter being delayed compared to the exhaust valves having a larger valve diameter, and the closing times of the exhaust valves being synchronized with each other.