JPH04103844A - Low nox engine - Google Patents

Abstract

PURPOSE:To suppress generation of NOx by setting the valve opening start timing of an intake valve later than a closing valve end timing, and inhibitiny any overlap of the valve opening timing of the intake valve over that of the exhaust valve. CONSTITUTION:The valve opening timing of an intake valve 4 in an intake stroke is set in a position later than the valve closing timing of an exhaust valve 5 so that the valve opening timings of the intake valve 4 and the exhaust valve 5 do not make any mutual overlap. In this case, scavenging efficiency is made proper and remaining exhaust gas is decreased by setting the valve opening timing of the exhaust valve 5 after the tab dead center (TDC) of a piston 2 T, D, C, but since the valve opening timing of the intake valve 4 is more delayed than the valve opening timing of the exhaust valve 5, an intake air quantity is decreased so as to improve an intake air throttle effect. Consequently, the quantity of NOx can be decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a low NOx engine that suppresses NOx generation by controlling the opening and closing timing of intake and exhaust valves of a four-cycle engine.

(Prior Art) Conventionally, in a four-stroke engine, as shown in Fig. 3, in order to smoothly suck air as the piston descends,
Move the intake valve to the piston top dead center (hereinafter referred to as T).

The intake valve is opened (indicated by IO in the diagram) before the piston bottom dead center (hereinafter referred to as B, D, and C) to ensure sufficient air intake. The exhaust valve is opened before B, D, and C in order to increase the air filling rate by opening the exhaust valve (indicated by IC in the figure) and to smoothly discharge exhaust gas as the piston rises. (denoted by EO in the diagram), and the exhaust valve is closed after T, D, and C (denoted by EC in the diagram) to increase the scavenging efficiency. ,D.

The opening timings of the valves overlapped in the area sandwiching C (indicated by X to Y in the figure).

(Problems to be Solved by the Invention) In the conventional system in which the opening timings of the intake valve and exhaust valve overlap, more fresh air flows into the cylinder, resulting in a faster combustion rate and a lower combustion peak temperature. There was a problem in that the amount of NOx in the exhaust gas increased as the amount of NOx became too high.

In order to solve this problem, intake throttling, exhaust throttling, or exhaust gas recirculation (hereinafter referred to as EGR) has conventionally been performed.

(Means for Solving the Problems) The present invention changes the valve timing of such conventional engines to eliminate the overlap between intake valve opening and exhaust valve closing.
By reducing the amount of intake air into the cylinder and allowing some of the exhaust gas to remain, lowering the combustion speed and therefore the combustion peak temperature, we can lower the NOx content in the exhaust gas and eliminate the need for various countermeasure devices. This is the purpose.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to FIGS. 1 and 2.

Figure 1 A, C, C, and D show the states of the piston and intake and exhaust valves during the intake stroke, compression stroke, explosion stroke, and exhaust stroke, respectively, in a 4-cycle engine, and E and F show the opening and closing of the intake and exhaust valves. Timing is expressed in crank angle.

Further, FIG. 2G shows the intake and exhaust valve timing in another embodiment, and FIG. 2H shows the intake and exhaust valve timing in yet another embodiment.

In the figure, 1 is a cylinder, 2 is a piston, 3 is a cylinder head, 4 is an intake valve, 5 is an exhaust valve, T, D,
C is the piston top dead center, B, D, C are the piston bottom dead center, I
O is intake valve open, IC is intake valve closed, EO is exhaust valve open, EC
indicates the exhaust valve closed position. Further, the arrows represent the vertical movement of the piston.

As Example 1, after the piston 2 starts to descend in the intake stroke shown in FIG. Air is sucked in as the air increases. Immediately after the piston 2 reaches B, D, and C, the intake valve 4 closes (IC angle E).

Next, in the compression stroke shown in FIG. 1, both the intake and exhaust valves 4 and 5 are closed.

Next, in the explosion stroke shown in FIG. 1C, the fuel in the cylinder 1 is ignited and an explosion occurs, and the piston 2 moves downward again.

At the end of the explosion stroke, just before the piston 2 reaches B, D, and C, the exhaust valve 5 opens (angle of EO to).

Furthermore, in the exhaust stroke shown in Figure 1, as the piston 2 reverses and rises, the exhaust gas in the cylinder is discharged, and the exhaust valve 5 moves the piston 2 to T and D.

closes before reaching C (angle of EC to).

In this case, by opening the intake valve 4 after T, D, and C, the amount of intake air is reduced and the same effect as the intake throttle can be obtained. Also, close the exhaust valve 5 at T and D.

By setting it before C, a part of the exhaust gas remains in the cylinder, and the same effect as EGR can be obtained.

Further, the opening timing 10 of the intake valve 4 is after the piston 2 has started to move down, and the closing timing EC of the exhaust valve 5 is after the piston 2 has started to move down.
Since this is before the engine has fully risen, there is no mutual interference between the intake and exhaust valves 4.5 and the piston 2, unlike in conventional engines.
There is no need to provide a gap (margin) between the uppermost position of the piston (T, D, C) and the bottom surface of the intake/exhaust valve.

This means that the waste volume around the intake and exhaust valves 4.5 is reduced, and the air utilization rate of the cylinder 1 is increased.
Various characteristics such as improved engine output, reduced fuel consumption, and reduced NOx can be expected, and there is also the advantage that combustion control can be designed as desired.

As a second embodiment, in FIG. 2G, the opening timing IO of the intake valve 4 in the intake stroke is set before T, D, and C, and the closing timing EC of the exhaust valve 5 in the exhaust stroke is set before IO. Set it so that it is further forward.

In this case, the intake valve 4 opens before T, D, and C, so there is a lot of intake air, which prevents air shortage during high-speed rotation.
If this continues, NOx will not decrease.

However, in order to eliminate overlap, the opening of the exhaust valve 5 is inevitably accelerated, which increases the amount of remaining exhaust gas, causing the EG
The R effect is enhanced, and NOx can be reduced as a result.

Furthermore, as a third embodiment, in FIG. 2 H, the closing timings EC of the exhaust valve 5 in the exhaust stroke are T and D.

In order to prevent the intake and exhaust valve timings from overlapping, the opening timing IO of the intake valve 4 in the intake stroke is set to a position later than EC.

In this case, the opening timing EC of the exhaust valve 5 is T, D.

Since it is set after C, the scavenging efficiency is good and residual exhaust gas is reduced, but since the opening timing 10 of the intake valve 4 is further delayed than EC, the amount of intake air is reduced, and the effect of intake throttling is increased. It is possible to reduce NOx significantly.

In addition, in each embodiment, the intake valve 4 is
It is desirable that the maximum lift of the piston 2 is delayed from the maximum speed of the piston 2 so as not to reduce the air filling rate as much as possible.

Also, the closing timing rc of the intake valve 4 and the opening timing E of the exhaust valve 5
O is preferably B or D for the following reasons.

It is desirable to approach C. That is, by bringing the closing timing IC of the intake valve 4 closer to B, D, or C, the actual compression ratio can be increased and the fuel ignition timing can be delayed by the amount of the increase in compression temperature, thereby making it possible to reduce noise.

Furthermore, by bringing the opening timing EO of the exhaust valve 5 closer to B, D, and C, combustion delays can be compensated for and HC emissions can be reduced.

(Effect of the invention) From the above, in the embodiment of the present invention, since the overlap in the opening timing of the intake and exhaust valves is eliminated, the NO.
Intake throttle, exhaust throttle, which were necessary to prevent x reduction,
Alternatively, it eliminates the need for various devices such as EGR, improves air utilization efficiency, facilitates low NOx design through combustion control, and is expected to improve overall engine output, reduce fuel consumption, reduce noise, and reduce HC. It can have a great effect on improving combustion.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the piston position, intake/exhaust valve status, and intake/exhaust valve timing of each stroke in a four-cycle engine according to an embodiment of the present invention, and Fig. 2 is an explanation of intake/exhaust valve timing in another embodiment of the present invention. 3 are explanatory diagrams of intake and exhaust valve timing in a conventional example. 1... Cylinder, 2... Piston, 3... Cylinder head, 4... Intake valve, 5... Exhaust valve.

Claims (1)

[Claims] In a drive mechanism for intake and exhaust valves of a 1- and 4-cycle engine, the opening timing of the intake valve is set later than the closing timing of the exhaust valve, and the intake valve and the exhaust valve are opened. Low NOx, characterized by a structure in which the timings do not overlap.
engine. 2. Set the intake valve opening timing to be after the piston top dead center, and
The exhaust valve closing timing is set before the piston top dead center.
A low NOx engine according to claim 1. 3. The low NOx engine according to claim 1, wherein the opening timing of the intake valve is set before the piston top dead center. 4. The low NOx engine according to claim 1, wherein the closing timing of the exhaust valve is set after the piston top dead center.