JPS6242134B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a cylinder head for a four-stroke engine having three or more intake valves per cylinder.

A plurality of intake valves are provided in order to expand the intake passage area of the intake valve and reduce intake resistance, and one intake valve is arranged near the center of the cylinder bore in order to weaken the masking effect of the intake air by the inner surface of the cylinder. has been proposed by the same applicant (for example, Japanese Patent Application No. 56-69099). In this case, the idea is to tilt three or more intake valves per cylinder so that they are parallel to each other in the same direction with respect to the cylinder, and open and close all the intake valves simultaneously using one valve lifter or one pressing plate. (For example, Japanese Patent Application Nos. 56-70331 and 56-70332). However, in this case, if intake valves with the same valve shaft length are used to share the parts of each intake valve,
The problem arises that the combustion chamber becomes deep, especially near the center of the bore, and that the compression ratio decreases and the S/V ratio (combustion chamber surface area/volume ratio) increases, resulting in a decrease in efficiency. Furthermore, since a large stepped portion is formed on the inside of the combustion chamber, uneven combustion tends to occur, making it difficult to operate with a lean mixture. This has resulted in disadvantages such as poor fuel efficiency and disadvantages in terms of exhaust gas countermeasures.

On the other hand, if the intake valve near the center of the bore is located deep in the combustion chamber, it is necessary to install the adjacent exhaust valve in a shallow position in the combustion chamber to increase the compression ratio as much as possible. The wall thickness on the cylinder head side that holds the valve seat of a high-temperature exhaust valve becomes thinner, making the valve seat more likely to deform due to thermal strain. There also arises a problem that the durability of the vicinity of the valve seat is also reduced.

The present invention has been made in view of these inconveniences. Three or more intake valves are provided per cylinder in parallel with each other so as to be inclined with respect to the cylinder, and one intake valve is arranged in the bore of the cylinder. In a 4-cycle internal combustion engine located near the center, it increases the compression ratio, reduces the S/V ratio, improves fuel efficiency and exhaust emissions, and prevents thermal deformation of the valve seat, improving its durability. The object of the present invention is to provide a cylinder head that can

In order to achieve such an object, the present invention biases the valve seat of the intake valve near the center of the bore toward the inside of the combustion chamber in parallel to the valve axis relative to the valve seats of other intake valves,
The combustion chamber is formed shallowly near the center of the bore. The present invention will be described in detail below based on embodiments shown in the drawings.

Fig. 1 is a valve arrangement diagram in an embodiment of the present invention, Fig. 2 is a perspective view of its intake passage, Fig. 3 is a sectional view taken along the line - - in Fig. 1, and Fig. 4 is an exploded perspective view of the intake valve. It is a diagram. In FIG. 1, reference numeral 10 is a cylinder, 12 is a bore center of this cylinder 10, and 14 is an axis of symmetry passing through this bore center 12. 16, 16A to 16D are intake valves, and one intake valve 16A is located at the center of the bore 12.
The intake valve 16B is located above the axis of symmetry 14.
located above. The other intake valves 16C, 16D are positioned symmetrically to the axis of symmetry 14, sandwiching the intake valves 16A, 16B on the axis of symmetry 14. 1
8, 18A to 18C are exhaust valves, and 18
The valves 18A are located on the axis of symmetry 14 opposite to the intake valve 16B, and the other exhaust valves 18B,
18C sandwiches the exhaust valve 18A and the axis of symmetry 14
It is arranged symmetrically with respect to the 20,
20A and 20B are spark plugs, and intake valves 16C and 16D and exhaust valves 18B and 18C, respectively.
They are arranged symmetrically with respect to the axis of symmetry 14 between them.

In FIG. 3, 21 is a piston that slides within the cylinder 10, 22 is a cylinder head, and 23 is a combustion chamber. Two intake passages 24, 24A, and 24B (see FIG. 2) are formed in the cylinder head 22, and each of these intake passages 24 further branches within the cylinder head 22, and an intake valve 16C or an intake valve 16C on the same side as each passage 24 or 16D and the intake valves 16A, 16B on the axis of symmetry 14. Exhaust passage 26 communicates with exhaust valves 18A-18C.

As is clear from FIGS. 3 and 4, the four intake valves 16A to 16D are inclined parallel to each other toward the intake passage 24, and are connected to valve guides 28, 28A,
28B is shown). Each valve shaft 30 (30A to 3
0D) has a fourth shaft end 32 (32A to 32D).
As shown in the figure, the kotta 34 (34A to 3) is divided into two parts.
4D), the valve spring 4 is fixed between the retainer 36 and the retainer 38 (38A to 38D, only 38A and 38B are shown) that is locked to the valve guide 28.
0.40A to 40D are compressed. Due to the spring force of the valve spring 40, the umbrella portion 42 of the valve 16,
The peripheral edges of 42A to 42D are the valve seats 44 (44A to 44
D, however, only 44A and 44B are shown) in the combustion chamber 2
The valves 16 are pressed from the third side, and the valves 16 are urged in the direction of closing.

Among the four intake valves 16, the valve 16A located on the bore center 12 has a valve shaft 30A that is longer than the valve shafts 30B to 30D of the other valves 16B to 16D, and correspondingly, the valve seat 44A is longer than the other valve shafts 30B to 30D. Valve seat 44B
~44C, it is biased toward the inside of the combustion chamber 23 in parallel with the valve shaft 30. That is, the shaft ends 32A to 32D of each of the valve shafts 30A to 30D are 1 perpendicular to each valve shaft 30.
The umbrella parts 42B to 42C are also located on one plane orthogonal to each valve shaft 30, but the valve shaft 30A of the valve 16A is located on the other valve shaft 30B.
30D, the valve seat 44A enters further into the combustion chamber 23 than the other valve seats 44B to 44D by the difference in length of the valve shaft 30. Therefore, the vicinity of the bore center of the combustion chamber 23 becomes shallow.

The three exhaust valves 18 are inclined in parallel to the exhaust passage 26 side, and each has a valve spring 46 (46A to 46
The valve shaft ends 48 (48A to 48C, only 48A is shown) are located on the same plane orthogonal to each valve 18. Note that 50 (50A to 50C, similarly only 50A is shown) is a valve seat of the exhaust valve 18.

The intake valve 16 and the exhaust valve 18 are inclined toward the intake passage 24 and the exhaust passage 26, respectively, and both valves 16 and 18 form a substantially V-shape as shown in FIG. 3. An ignition plug attachment/detachment hole (not shown) is formed in this V-shaped space, and the spark plug 20 is attached/detached through this attachment/detachment hole.

Reference numeral 52 denotes a valve lifter on the intake side, which, as shown in FIG. 4, includes a side plate portion 54 and an upper plate portion 56, and is formed as a whole into a lid shape having a substantially rhombic planar shape. As shown in FIG. 3, the valve lifter 52 has a side plate 54 guided by the cylinder head 22 so as to be slidable in the same direction as the valve 16. The inner surface (lower surface) of the upper plate portion 56 of this valve lifter 52 faces the valve shaft end 32 of each valve 16 via pads 58, 58A to 58D, respectively.

Reference numeral 60 denotes a valve lifter on the exhaust side, which is formed in the shape of a lid to cover above the valve shaft ends 48A to 48C of the exhaust valve 18, and is slidable in parallel with the valve 18 while being guided by the cylinder head 22. The valve shaft end 48 faces the inner surface of the upper plate portion 62 of the valve lifter 60 via pads 64 (64A to 64C, only 64A is shown).

66 is an overhead camshaft on the intake side, and 68 is an overhead camshaft on the exhaust side. Both camshafts 66 and 68 are rotatably held in the cylinder head 22 so as to be orthogonal to the axis of symmetry 14 (FIG. 1). and rotates at half the speed of the crankshaft (not shown) in synchronization with the crankshaft (not shown). Two cams 70, 72 are formed on each of the cam shafts 66, 68, and each of these cams 70, 7
2 abuts on the upper surfaces of the valve lifters 52, 60 via pads 74, 74A, 74B, 76.
Note that these pads 74 and 76 are slightly eccentric in the longitudinal direction of the camshafts 66 and 68 with respect to the cams 70 and 72, and rotate at a low speed as the camshafts 66 and 68 rotate, causing uneven wear of the cams 70 and 72. is prevented.
Furthermore, when the cams 70, 72 press the valve lifters 52, 60, the cam shafts 66, 68 and the positions of cams 70, 72 are determined. Therefore, the valve lifters 52 and 60 press the valves 16 and 18 in parallel with each other with equal pressing force, and no unreasonable force is generated in the direction of tilting the valve lifters 52 and 60.

Now, in the intake stroke, if the cam 70 of the intake side camshaft 66 presses the valve lifter 52 downward via the pad 74, each valve 16 is simultaneously and equally pressed downward, and the umbrella part 42 of each valve 16 is pressed against the valve seat 44.
The valve 16 opens. At this time, the piston 21 enters a downward process, and intake air flows into the combustion chamber 23 from the intake passage 24. The valve seat 44A and the umbrella portion 42A of the valve 16A near the bore center 12 are
Valve seats 44B to 44D of other valves 16B to 16D
Since the umbrella portions 42B to 42D enter into the combustion chamber 23, there is a step between the valve seat 44A and the valve seats 50 of the three exhaust valves 18 adjacent thereto;
That is, the difference in depth of the combustion chamber 23 at the closest portion 78 (FIG. 3) between the valve seats 44 and 50 is small.
Therefore, the intake air flowing into the combustion chamber 23 from the intake valve 16A is not blocked by the step near the closest portion 78, and flows smoothly. In other words, the masking effect of the intake air due to the step near the closest portion 78 is weakened, and the intake efficiency is improved.

Further, since the combustion chamber 23 becomes shallow near the intake valve 16A, it is possible to increase the compression ratio and decrease the S/V ratio (surface area/volume ratio of the combustion chamber), thereby improving thermal efficiency.

When the flame is ignited by the spark plug 20 after the compression stroke, it propagates within the combustion chamber 23, but since there are few steps near the closest portion 78, the flame propagates smoothly without being almost blocked by this step. , uneven combustion in each cycle is less likely to occur. This makes irregular combustion less likely to occur, so
Operation with a leaner air-fuel mixture becomes possible, and as a result of the above-mentioned increase in compression ratio and decrease in S/V ratio, fuel efficiency can be significantly improved. Further, by using a lean mixture, exhaust gas can be purified.

In the exhaust stroke, the valve lifter 60 is pressed downward by the cam 72 of the camshaft 68, and the exhaust valve 18 is opened. The valve seat 50 becomes high temperature because it is exposed to high temperature exhaust gas. However, each exhaust valve 1
Since the step of the closest portion 78 where the cylinder head 8 is close to the intake valve 16A is small, the cylinder head 22 does not protrude toward the combustion chamber 23 in a thin state on the intake valve 16A side of the valve seat 50. This not only improves the heat transfer to the cylinder head 22 on the intake valve 16A side of the valve seat 50, but also makes it difficult for thermal distortion to occur in the portions of the cylinder head 22 surrounding the valve seat 50 and the valve seat 50. The durability of the material is improved.

In this embodiment, only the intake valve 16A is lengthened and the other valves 16B to 16D are made the same length, but the valve 16B closer to the inclination direction of the valve 16 (leftward in FIG. 3) is made the shortest, and the valve 16B in the opposite inclination direction The located valves 16C, 16D and 16A are lengthened in sequence to form umbrella parts 42B, 42C, 42D and 42A.
may be arranged in a stepped manner.

As described above, this invention makes the valve seat of the intake valve near the center of the bore more inward of the combustion chamber and parallel to the valve axis than the valve seats of other intake valves, making the area near the center of the bore of the combustion chamber shallower. This makes it possible to increase the compression ratio, decrease the S/V ratio, and improve combustion, thereby improving fuel efficiency and purifying exhaust gas. In addition, the intake valve near the center of the bore is hardly affected by the masking effect near the valve seat of the adjacent exhaust valve, improving intake efficiency. Furthermore, since the cooling performance of the valve seat of the exhaust valve and the strength of the cylinder head in the vicinity of the valve seat are improved, thermal deformation in the vicinity of the valve seat is less likely to occur and durability is improved.

[Brief explanation of the drawing]

Fig. 1 is a valve arrangement diagram in an embodiment of the present invention, Fig. 2 is a perspective view of its intake passage, Fig. 3 is a sectional view taken along the line - - in Fig. 1, and Fig. 4 is an exploded perspective view of the intake side valve. It is. 10...Cylinder, 12...Bore center, 16...
...Intake valve, 23...Combustion chamber, 30...Valve shaft,
44...Benza.

Claims (1)

[Claims] 1 Three or more intake valves per cylinder are provided parallel to each other so as to be inclined with respect to the cylinder,
In a four-stroke internal combustion engine in which one of the intake valves is arranged near the center of the bore of the cylinder, the valve seat of the intake valve near the center of the bore is arranged in the combustion chamber more parallel to the valve axis than the valve seats of other intake valves. 1. A cylinder head for a four-stroke internal combustion engine, characterized in that the cylinder head is biased toward the cylinder head and is formed shallowly near the center of the bore of the combustion chamber.