JP2709261B2 - 4 cycle engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a four-stroke engine, and more particularly to the number and arrangement of intake and exhaust valves.

[0002]

2. Description of the Related Art A four-valve engine having two intake valves and two exhaust valves can have a larger valve area than a two-valve engine.
In terms of fuel efficiency, etc., it is superior to a two-valve engine. However, performance such as engine output and fuel efficiency,
It is determined by the size of the valve, the compression ratio, the combustion state, etc., which are in conflict with each other. That is, 4
In valved engines, the most appropriate values have been found for valve size, valve included angle, piston stroke and bore diameter, and even if these values are changed, the engine performance cannot be improved. Has been reached. Therefore, in the case of a four-valve engine, it is unlikely that the performance will be improved by devising the size of the valve in the future.

[0003] Thus, an eight-valve or five-valve engine has appeared (see, for example, Japanese Patent Application Laid-Open No. 61-185654). Examples of these are shown in FIG. 3 and FIG.

[0004]

However, an eight-valve engine has intake and exhaust ports 1 and 2 as shown in FIG.
The number 3 is too large, so that the piston and cylinder bore 3 has a non-circular cross section. Therefore, processing becomes difficult, and the manufacturability is significantly reduced. Therefore, it is used only for very special engines.

On the other hand, a five-valve engine is shown in FIG.
As shown in (1), although the cylinder bore 3 is circular, the productivity is lower than that of the 4-valve for the following reasons. That is, a five-valve engine has three intake ports 1A,
Since 1B and 1A are not arranged in a straight line, FIG.
As described above, since the included angles θa and θb of the intake valves 5A and 5B driven by one camshaft 4 are different from each other, the productivity is lower than that of four valves.

[0006] The present invention has been made in view of the above-mentioned conventional problems, and has as its object to provide a four-cycle engine having the same level of productivity as a four-valve engine and having better performance than a four-valve engine.

[0007]

In order to achieve the above object, the present invention provides three intake valves and three exhaust valves, respectively, and further defines an intake port opened and closed by the intake valve in plan view. The exhaust ports arranged substantially linearly and opened and closed by the exhaust valve are linearly arranged substantially parallel to the intake port in plan view, and are surrounded by the two intake ports and the exhaust port. A spark plug is provided at each of two locations.

According to the present invention, since the intake and exhaust ports are arranged substantially in a straight line in a plan view, the included angle is the same for each intake and exhaust valve.

[0009]

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1 (a), in the four-cycle engine, the cylinder bore 3 has a circular cross section, and
It has three intake valves 5 and three exhaust valves 6, respectively. The three intake ports 1 opened and closed by the intake valves 5 are arranged on a straight line when viewed from above the cylinder axis Sc in FIG. 1B, that is, in a plan view in FIG. 1A. On the other hand, the three exhaust ports 2 opened and closed by the exhaust valve 6 are arranged in parallel with the intake port 1 and on a straight line in a plan view. The area of the intake port 1 is larger than the area of the exhaust port 2, and the intake port 1 is arranged closer to the center line Bc of the cylinder bore 3 than the exhaust port 2. A spark plug 7 is provided at a location surrounded by the two intake ports 5 and the two exhaust ports 6, respectively. The combustion chamber 8 shown in FIG.
Is, for example, a pent roof type.

Next, the performance of the six-valve engine will be described in comparison with a conventional four-valve engine. First, a comparison between the output and the fuel efficiency will be described. 6
The intake and exhaust valves 5 and 6 of the valves are significantly smaller than the intake and exhaust valves 5 and 6 of the four valves in FIG. However, the intake and exhaust valves 5 and 6 of the six valves in FIG.
Are smaller than the intake and exhaust valves 5 and 6 of the four valves described above, so that they are close to the center Bc of the cylinder bore. Therefore, FIG.
The sum of the diameters φ of the three valves is slightly larger in the intake and exhaust valves 5 and 6 of the six valves than in the case of the four valves. Therefore, the circumferential length of the intake and exhaust valves 5 and 6 becomes longer, so that the intake and exhaust passage area obtained by multiplying the circumferential length of the intake and exhaust valves 5 and 6 by the stroke St in FIG. Since the area between the exhaust valve 6 and the valve seat 9 is increased, the resistance to the flow of intake and exhaust, that is, the masking is reduced.

In the four-valve engine shown in FIG. 2, since the valves 5 and 6 are large, the space S on the cylinder wall 3a side of the intake valve 5 is small. Therefore, the intake air M (or exhaust gas) shown in FIG. 2C collides with the cylinder wall 3a, and the flow thereof is easily obstructed. On the other hand, in the six-valve engine shown in FIG. 1A, since the valves 5 and 6 are small, the space S on the cylinder wall 3a side of the intake valve 5 is large. Therefore, as shown in FIG. 1C, since the intake air M is smoothly guided into the cylinder 10 by the cylinder wall 3a, the flow of the intake air M (or the exhaust gas) becomes smooth, and the masking is reduced.

Further, since the valve diameter of the six valves is small, the area of the portion (hatched portion) S1 where the intake and exhaust valves 5 and 6 in FIG. Since it is smaller than S2, the masking also becomes smaller.

The six intake and exhaust valves 5, 6 are
2B, the height H of the combustion chamber 8 above the piston (not shown) is reduced as shown in FIG. 1B. Therefore, since the combustion chamber 8 becomes small, a large compression ratio can be obtained even if the intake and exhaust valves 5 and 6 are made as large as possible.

Further, as shown in FIG. 1 (a), since the spark plug 7 is disposed in the space surrounded by the four valves 5 and 6, the propagation distance of the flame is shortened. By increasing the bore diameter, the stroke of the piston can be reduced. Therefore, larger intake and exhaust valves 5,
6 can be adopted.

Further, since the two spark plugs 7, 7 are provided, if the ignition timings of the two spark plugs 7, 7 are different from each other, the torque curve of the engine output can be smoothed. Therefore, the waste of work is reduced, and the fuel efficiency is also improved.

As described above, in this six-valve engine, the masking is reduced and the compression ratio is increased.
Further, since the torque curve can be smoothed as required, the output of the engine and the fuel consumption are improved as compared with the case of four valves.

Next, the idling state and the limit of the engine speed will be compared. In the six valves of FIG. 1A, as described above, since the masking is reduced, the negative pressure of the intake air is increased even if the opening timing of the intake valve 5 is narrowed. Therefore, the idling state is stabilized.

The diameter of the intake and exhaust valves 5 and 6 of the six valves is approximately (2/3) times that of the four valves of FIG. Therefore, the area of the valve alone is about (4
/ 9) times the total area of the four intake valves 5
Assuming that A, the total area of the three intake valves 5 of the six valves is 3 × (4/9) · A = (4/3) · A, and therefore the total area of the valves is small, so that The total weight is also reduced. Therefore, the intake and exhaust valves 5 and 6 in FIG.
Since the total load of the valve spring (not shown) for restoring is also reduced, the torque fluctuation of the valve train is reduced, and the rotation fluctuation during idling is reduced.
The idling state is stabilized. Also, mechanical loss and mechanical noise are reduced.

As described above, since the intake and exhaust valves 5 and 6 become lighter with the six valves, the inertial force when the valves reciprocate is reduced. Therefore, the limit of the number of revolutions caused by the valve train is greatly improved. If the limit of the number of revolutions is determined not by the valve train but by the piston-crank system, as described above, the combustion propagation distance becomes shorter and the compression ratio becomes larger. Can be reduced to increase the rotational speed limit.

Next, a comparison with a conventional five-valve will be described. As shown in FIG. 1A, this six-valve engine has three intake ports 1 (and exhaust ports 2).
Since each is arranged on a straight line, even if the included angle θ of each intake valve 5 in FIG. 1B is set to the same value, one intake cam shaft and one exhaust cam shaft (not shown) The intake and exhaust valves 5, 6 can be operated. Therefore, unlike the five-valve engine shown in FIG. 4B, there is no need to use two types of the included angles θa and θb of the intake valves 5A and 5B, so that machining is facilitated and productivity is improved.

In the five valves, the intake valves 5A, 5A
Since the included angles θa and θb of B are different from each other, the shape of the upper portion of the combustion chamber 8 is not smooth, and therefore, the propagation speed of the flame is reduced, which causes the output to decrease. On the other hand, in the case of the six valves in FIG. 1, the included angle θ (FIG. 1B) of the three intake valves 5 becomes the same, so that the shape of the upper part of the combustion chamber 8 becomes smooth. Therefore, the propagation speed of the flame becomes faster than 5 valves.

Further, regarding the masking of the intake air,
As described in comparison with the valve, the intake valve 5 in FIG.

In the case of the five valves shown in FIG. 4A, two ignition plugs cannot be provided due to the arrangement of the five intake and exhaust valves 5 and 6. On the other hand, in the six valves of FIG. 1A, the intake valve 5 and the exhaust valve 6 are arranged in a straight line in parallel with each other. Can be arranged.
Therefore, the propagation distance of the flame is shorter than 5 valves.

Further, by slightly differing the ignition timings of the two spark plugs, the torque curve of the engine output can be made smooth.

Thus, this six-valve engine is:
Compared to a 5-valve engine with the same bore stroke ratio,
As the flame propagation speed increases, masking improves, and the torque curve of the engine can be smoothed. Therefore, even if the area of the intake valve 5 is smaller than 5 valves, it is about the same as 5 valves. You can expect engine output.

In the five-valve engine shown in FIG. 4, since the number of exhaust valves 6 is two, the area of the exhaust valves 6, that is, the weight of one exhaust valve 6 is slightly smaller than that of the four valves. Absent. Therefore, the limit of the number of revolutions determined by the inertial force of the reciprocating valve does not increase as much. On the other hand, as described in comparison with the four valves in the six valves in FIG. 1, the limit of the number of revolutions is greatly improved.

Of course, in a six-valve engine, since the bore 3 is circular, machining of the piston and the bore 3 does not become extremely difficult, unlike an eight-valve engine.

In the present invention, the three intake ports 1 and the exhaust ports 2 may be arranged substantially in a straight line, and may be arranged substantially parallel to each other.

[0029]

As described above, according to the present invention, not only three intake / exhaust valves are provided but also three intake ports and exhaust ports are arranged substantially in a straight line in parallel with each other, and Since two spark plugs are provided, the engine output and the fuel efficiency are improved as compared with the four-valve valve without lowering the manufacturability of the five-valve and eight-valve valves, and a good idling state is obtained. Furthermore, the limit of the number of rotations can be improved.

In particular, this six-valve engine has a higher flame propagation speed, improved masking, and a smoother engine torque curve than a five-valve engine having the same bore stroke ratio. Therefore, even if the area of the intake valve is smaller than that of the five valves, an engine output equivalent to that of the five valves can be expected. Also, by changing the bore stroke ratio to increase the bore diameter and reduce the piston stroke as compared to a five-valve engine, the intake valve area, compression ratio, and flame propagation speed equivalent to the five-valve engine can be obtained. In addition, the masking and rotation limits are improved, and the size of the exhaust valve can be increased. As a result, an engine with a higher output and higher performance than a five-valve engine can be obtained.

[Brief description of the drawings]

FIG. 1 is a plan conceptual diagram and a longitudinal sectional conceptual diagram showing one embodiment of a four-cycle engine of the present invention.

FIG. 2 is a conceptual diagram of a conventional four-valve four-cycle engine.

FIG. 3 is a conceptual plan view of an eight-valve four-stroke engine.

FIG. 4 is a conceptual diagram of a five-valve four-cycle engine.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Intake port, 2 ... Exhaust port, 3 ... Bore, 5 ... Intake valve, 6 ... Exhaust valve, 7 ... Spark plug.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location F02P 15/08 302 F02P 15/08 302A

Claims (1)

(57) [Claims] 1. A four-stroke engine having a plurality of intake valves and exhaust valves and having a circular cylinder bore is provided with three intake valves and three exhaust valves, each of which is opened and closed by the intake valves. Intake port
In a plan view, the exhaust ports that are arranged substantially in a straight line, and that are opened and closed by the exhaust valve, are arranged in a straight line almost in parallel with the intake ports in a plan view, and are arranged in the two intake ports and the exhaust port. A four-stroke engine, characterized in that spark plugs are provided in two enclosed portions, respectively.