JPS6185516A - Variable valve timing mechanism - Google Patents

Abstract

PURPOSE:To realize such a valve characteristic that accords with engine running conditions, by raising each lift of both suction and exhaust valves, improving exhaust capacity ever so better, while adjusting valve timing so as to keep off any interference between a piston head part and the valve. CONSTITUTION:In an on-off mechanism for a suction valve or an exhaust valve, there are provided with a device adjusting a lift value of the valve and another device adjusting on-off timing of the valve. When an engine is driven at high speed and high load to valve characteristics A and B in the exhaust valve and the suction valve being set up so as to accord with low engine speed, the lift value of the suction valve or the exhaust valve is made to be larger and a valve opening period is made to be longer whereby suction capacity or exhaust capacity is improved. In order to keep off any interference between a piston head part and the valve due to an increase in the lift value, timing of the suction valve or the exhaust valve is adjusted, making it to be just like a valve characteristic B', and a clearance l between the piston head part and the valve is secured. With this constitution, suction-exhaust capacity is improved and a dead space in a combustion chamber is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is useful for improving engine performance by increasing the valve interval and valve lift on the exhaust valve side of a diesel engine in which the intake and exhaust valves are operated by independent cam mechanisms. The present invention relates to a suitable variable valve timing mechanism.

[Conventional technology]

Conventionally, the valve timing of an engine's intake and exhaust valves is fixed regardless of changes in engine speed. Under these conditions, the valve timing was not optimal, resulting in incomplete combustion due to a lack of intake air, resulting in problems that degraded engine performance.

For this reason, even in the conventional technology, for example,
As shown in 2008 and Utility Model Application Publication No. 56-20016, a valve opening timing control device that advances or retreats the valve timing and a valve operating device that changes the valve lift have been proposed, but the former focuses on valve timing at low rotation speeds. The latter focuses on eliminating valve overlap during startup and warm-up, and does not directly solve the above problems, and does not take into account interference between the intake and exhaust valves and the piston.

In diesel engines, it is necessary to increase the compression ratio, so changing the valve timing causes the intake and exhaust valves to be too close to the piston from the end of the exhaust stroke to the beginning of the intake stroke, that is, the period of valve overlap. A problem that interferes with this occurs.If a valve relief is formed in the piston head to prevent this interference, the dead volume, which is a gap outside the combustion chamber, increases, resulting in a problem that the compression ratio decreases and the combustion efficiency decreases.

[Problem that the invention seeks to solve]

The present invention has been devised to solve the above-mentioned problems, etc., and its purpose is to improve engine performance especially during engine acceleration and high-speed light load operation, and to reduce pumping loss during high-speed rotation and low load operation. It is an object of the present invention to provide a variable valve timing mechanism that improves fuel efficiency and prevents interference between a piston and an exhaust valve.

[Means for solving problems]

In order to achieve the above object, the present invention provides an engine exhaust valve in which the intake and exhaust valves are each operated by an independent cam mechanism, or a lift valve on the intake valve side (in which the valve lift is increased on one side to increase the valve interval). The variable valve timing mechanism is characterized in that the independent cam mechanism is provided with an adjusting means and a variable advance means that advances or retards the valve timing of the exhaust valve or the intake valve, respectively. be.

〔Example〕

Embodiments of the present invention will be described below based on the drawings and the like.

As the variable advance angle means 1 for advancing and retracting the valve timing, there are various known techniques as partially disclosed in Japanese Utility Model Application Publication S55-4SOS, for example, the one shown in FIG. 1 is cited. That is, there is a sleeve 6 between the helical spline y3a formed on one end side of the cam 1 wheel 2 and the helical spline 3b formed on the one end side of the camshaft 5 of the cam 4 for the exhaust valve.
will be erected. Helical splines 3a and 3b are formed with opposite helix angles. A binion 7 meshes with rack teeth 6a formed on the outside of the sleeve 6, and the binion 7 is rotated by a pulse motor 8.

With the above configuration, the sleeve 6 is moved by the rotation of the pulse motor 8, giving a desired advance angle to the cam 4, and the valve timing is advanced or retreated.

Note that the exhaust cam 4 and the intake cam (not shown) are similar to a twin cam mechanism (they are formed separately, so changing the exhaust side valve timing will have no effect on the intake side valve timing. As the lift adjustment means 10, for example, a known hydraulic tappet as shown in FIG. It is formed from a plunger 12 etc.,
When oil is supplied into the oil chamber 11, the tappet 9 moves with no play (moves) according to the lift of the cam 4, but when oil is not supplied, a certain amount of play is formed.

During normal IT engine operation, the above play is maintained in order to prevent the valve from being pushed up due to thermal expansion of various parts, resulting in incomplete closing of the valve. Therefore, the valve lift increases by the amount of play due to oil supply, and the valve interval can be increased.

FIG. 3 is a diagram showing the valve timing of the engine intake and exhaust valves, where the horizontal axis shows the crank angle θ and the vertical axis shows the valve lift H. Curve A shows the exhaust valve side, and curve B shows the intake valve side.

Curves A and B indicated by dotted lines indicate the optimal valve timing when the engine is running at high speed, and point a is the intake valve [! (10), dots indicate intake valve closed (IC), point C indicates exhaust valve open (E (J)), and point d indicates exhaust valve closed (EC).

Also, since there is play ΔH, curves A and B are at point a0. bol
It is formed from the CO+dO position. Further, in the figure, the symbol BDC indicates the bottom dead center of the piston, and TDC indicates the top dead center of the piston.

The curved line indicates the locus of the piston head, and a clearance j is formed between the piston head and curves A and B in the vicinity of TDC, and the two do not interfere.

Curves A and B are, as mentioned above, at engine high speeds 1. -The valve timing is matched under load to ensure high output.

On the other hand, especially in engines with exhaust turbos, exhaust gas is used to accelerate the engine, and with the above valve timing curve, exhaust gas is insufficient during acceleration or at high speeds and low loads. Therefore, it is necessary to widen the valve interval.

The curve IwA" (indicated by a dashed line) shows this. By reducing the play ΔH of the lift adjusting means 10 to zero, the valve lift increases, and the valve interval increases as shown between points C" and d". However, as shown in the figure, when the valve lift is increased, the clearance j disappears, causing a problem in which the piston head and the exhaust valve interfere. Therefore, the valve timing only on the exhaust valve side is advanced by the variable advance means lK. Make sure that clearance l occurs.Song 11
IA' (actual #) indicates this, point C'' is connected to point C', point l
moves to point d', but the valve interval remains unchanged. Further, the overburden amount between point a and point 6 becomes point a and point d', but does not change much.

In this case, during acceleration, etc., the exhaust characteristics are improved by changing the valve timing curve as shown in curve A' by the advance angle l and lift adjustment means 10.Of course, at high speed and high load, by changing the valve timing curve The normal state is restored.Furthermore, the pulp timing can be made variable even at intermediate stages such as medium speed to improve efficiency.

FIG. 4 is a diagram showing the case where the intake valve side is lifted up and the timing is delayed, and the symbols are the same as those in FIG. 3.

In this embodiment, curves A and B are pulp timings that are matched at low speeds, and if left as they are, the intake efficiency will be insufficient at high speeds and high loads, making it difficult to produce high output. Therefore, it becomes necessary to widen the valve interval.

The curve HB" (indicated by a dashed line) shows the play ΔH of the lift adjusting means IO is made zero and the valve lift is increased by that amount. As shown between point a" and point ♂, the valve interval widens and the intake t increases.

However, as shown in the figure, when the valve lift is increased, the clearance l becomes nonexistent, resulting in a problem in which the piston head and the intake valve interfere with each other.

Therefore, the pulp timing only on the intake valve side is delayed by the variable advance means so that the clearance l is generated. Curve B' (solid line) shows this, point a'1 is point a' K,
Point d' moves to point b', but the valve interval is at point a.
' and point b' and remains unchanged. Further, the amount of overlap between point a and point 6 becomes point a' and point d, but hardly changes.

In this case, list a is used at high speed and red load.
By changing the curve B to the curve B by the MIE means 10 and the advance angle means 1, the intake characteristics are improved.Of course, at low speeds, returning to the original state returns to the normal state. etc.) The intermediate stage 1 vs ′-1 is also
°1°yyyq change & L efficiency can be improved.

In this embodiment, the advancing means 1 and the adjusting means 1
0 has been explained, but it goes without saying that the number is not limited to these.

〔Effect of the invention〕

As is clear from the above description (according to the present invention), it is possible to improve engine performance particularly during engine acceleration, high speed and low load, or high speed and high load, and also to prevent interference with the piston. It can be raised.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram for explaining the advance angle means of the present invention, FIG. 2 is a sectional view showing an example of the lift adjusting means, and FIGS. 3 and 4 are diagrams showing pulp timing.

Claims (1)

[Claims] A lift adjusting means for increasing the valve interval by increasing the valve lift is provided on at least one of the exhaust valve or intake valve side of an engine in which the intake and exhaust valves are each operated by an independent cam mechanism, and the exhaust valve or the intake valve is A variable valve timing mechanism characterized in that the independent cam mechanism is provided with variable advance means for respectively advancing or retarding the valve timing of the valve.