JPH041418A - Two-stroke internal combustion engine - Google Patents

Abstract

PURPOSE:To improve engine performance in a wide operating region by lessening the operating angles of an air supply valve and an exhaust valve, and timing-advancing an operating center angle with the transfer of an engine speed from a high revolution region to a low revolution region. CONSTITUTION:Fuel is injected from a fuel injection valve 7 at the vicinity of the compression top dead center of a piston 3. An exhaust valve 6 is opened in the latter half of a combustion stroke to exhaust a burnt gas from a combustion chamber 4, and also an air supply valve 5 is opened at this side of the bottom dead center to pressedly feed fresh air. In this case, in a variable valve mechanism 10 opening and closing the air supply valve 5 and the exhaust valve 6, a valve operating angle is made small and an operating center angle is timing-advanced in an engine low revolution region, while an operating angle is made large and an operating center angle is timing-delayed in a high revolution region. Consequently the overlapped quantity of the air supply and exhaust valves is lessened in the low revolution region and is expanded in the high revolution region. As a result, the blow-by of the fresh air can be reduced so as to lessen the work loss of a supercharger in the low revolution region. Also air supply efficiency can be improved by utilizing inertia force in the high revolution region.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a two-stroke internal combustion engine with variable valve timing.

(Prior Art) Two-stroke internal combustion engines have a large overlap period between the intake valve and exhaust valve, and compared to four-stroke internal combustion engines,
Valve timing settings have a large impact on engine performance, including the flow of fresh air into the exhaust system.

The required characteristics of valve timing vary greatly depending on the operating conditions of the engine.
In Publication No. 631, when the engine is started, the closing timing of the intake valve is advanced, thereby reducing the amount of fresh air that returns to the intake system during compression, increasing the compression ratio, and improving the ignition performance at the time of engine startup.

(Problem to be solved by the invention) However, in the past, there was no concept of variably controlling the valve timing of the intake valve and exhaust valve in a wide operating range of the engine, and the current fuel consumption and The overall characteristics of the output are not always satisfactory.

The present invention aims to solve such problems.

(Means for Solving the Problems) Therefore, the present invention provides a two-stroke internal combustion engine equipped with an intake valve that opens during the intake stroke of an engine, and an exhaust valve that opens during the exhaust stroke, and a supercharger in the intake air system. The engine is provided with a variable valve mechanism that advances the operating center angle of the supply and exhaust valves in a lower rotation range, and also decreases the operating angle in a lower rotation range.

(Function) In the high rotation range, the operating angle and overlap period of the supply and exhaust valves become large, and the inertia effect can be used to increase the supply and exhaust efficiency. In contrast, in the low rotation range, the intake valve closes earlier, increasing the effective compression ratio, and shortens the overlap period of the intake and exhaust valves to reduce fresh air blow-through, improving fuel efficiency and output. be able to.

(Example) Embodiments of the present invention will be described below based on the drawings.

In Fig. 1, 1 is a cylinder head, 2 is a cylinder,
A piston 3 defines a combustion chamber 4. The cylinder head 1 is provided with an intake valve 5, an exhaust valve 6, and a fuel injection valve 7.

Although not shown, a supercharger is provided in the air supply passage upstream of the air supply valve, and pressurizes fresh air into the cylinder when the air supply valve 5 is opened.

A variable valve mechanism 10 for opening and closing the intake valve 5 and the exhaust valve 6 and changing the opening/closing timing according to engine rotation,
It is shown in FIG. 2 (A>(B)) and FIG.

The cam 11 for driving the intake valve 5 (the same applies to the exhaust valve 6) has a cam profile, that is, a cam lift and an operating angle that gradually change in the axial direction of the camshaft 12, and the operating center angle also changes. .

An actuator (not shown) is provided to drive the camshaft 12 in the axial direction according to engine rotation, and the cam profile changes as the camshaft 12 moves.

The movement of the cam 11 is then transmitted to the intake valve 5 via the rocker arm 14, and lifts the intake valve 5 against the valve spring 15.

Figure 4 shows the characteristic that the operating center angle (maximum lift) of the intake valve 5 and the exhaust valve 6 changes with the rotation speed. let

Further, as shown in FIG. 5, the operating angles (valve opening periods) of the intake valve 5 and the exhaust valve 6 are also set to become smaller as the rotation range shifts from the high rotation range to the low rotation range.

Next, the effect will be explained.

Fuel is injected from the fuel injection valve 7 near the compression top dead center of the piston 3, and compression ignition occurs. Exhaust valve 6 in the latter half of the combustion stroke
opens, and combustion gas is discharged from the combustion chamber 4, and at the same time, the air supply valve 5 opens just before bottom dead center, and fresh air is fed under pressure. The intake valve 5 and the exhaust valve 6 are used to introduce fresh air and discharge combustion gas.
This is done while overlapping the two.

As the piston 3 rises, the exhaust valve 6 first closes, and then the air supply valve 5 closes, thereby starting the compression action. The compressed air becomes hot near top dead center and ignites the injected fuel as described above.

By the way, the variable valve 81 that opens and closes the intake valve 5 and the exhaust valve 6
Lateral 10 reduces the valve operating angle and advances the operating center angle in the low engine speed range, while increasing the valve operating angle and retards the operating center angle in the high engine speed range.

As a result, the amount of overlap between the supply and exhaust valves becomes smaller in the low-speed range, and increases in the high-speed range.

The amount of fresh air that blows from the supply air system to the exhaust system during the overlap period of the supply and exhaust valves decreases as the engine speed increases. Therefore, by reducing the amount of overlap in the low rotation range, it is possible to reduce blow-by of fresh air and reduce work loss of the supercharger.

Further, by advancing the closing timing of the intake valve 5 in the low rotation range, the actual compression action starts earlier, and the effective compression ratio can be increased accordingly.

On the other hand, by increasing the overlap period in the high rotation range, it is possible to improve the air supply efficiency by utilizing inertia force, and it is possible to improve the fuel efficiency and output of the engine.

Figure 6 shows the relationship between engine speed and fuel consumption rate, and Figure 7 shows the relationship between engine speed and specific torque.The shaded area (in the direction of the arrow) in each figure shows the relationship between the engine speed and the fuel consumption rate, and the area shown in the diagram (in the direction of the arrow) is improved by the present invention. As a result, it can be seen that the fuel consumption rate decreases significantly and the specific torque increases, especially in the lower rotation range.

Note that the solid line shows the characteristics of a two-stroke internal combustion engine, and the dotted line shows the characteristics of a four-stroke internal combustion engine for comparison.

(Effects of the Invention) As described above, according to the present invention, as the engine speed shifts from a high speed range to a low speed range, the operating angles of the supply and exhaust valves are reduced and the operating center angles are advanced. As a result, a good inertial air supply effect is achieved in the high speed range, and by preventing fresh air from blowing out and increasing the compression ratio in the low speed range, fuel consumption and fuel efficiency are improved, respectively.
This has the effect of improving output characteristics and improving engine performance over a wide range of engine operation.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment of the present invention, and FIG. 2 (A>(
B) is a front view and side view of the cam, Fig. 3 is a side view of the valve train system, Fig. 4 is a control characteristic diagram of the valve operating center angle, Fig. 5 is a control characteristic diagram of the valve operating angle, and Fig. 6 is a characteristic diagram of fuel consumption rate, and FIG. 7 is a characteristic diagram of specific torque. 4... Combustion chamber, 5... Air supply valve, 6... Exhaust valve, 10
...Variable valve mechanism, 11...Cam, 12...Camshaft 9 Patent applicant Nissan Motor Co., Ltd. Figure 2 (A) Figure 2 (,8) Figure 3 Figure 4-m-S Buzz (Nara 11 ≧ Eni 5- Pure air valve (A to air well middle) (^'s word history - within ±3°CA Figure 5 Number of engines Figure 6 Turbocharger efficiency = 80 % Excess air ratio = 1.4 Geometric compression ratio = 18 Engine concave displacement pm

Claims (1)

[Claims] 1. In a two-stroke internal combustion engine equipped with an intake valve that opens during the intake stroke of the engine and an exhaust valve that opens during the exhaust stroke, and a supercharger in the intake air system, the central angle of operation of the intake and exhaust valves. 2, characterized in that it is equipped with a variable valve mechanism that advances the engine in the lower rotation range, and also reduces the operating angle in the lower rotation range.
Stroke internal combustion engine.