JPS638831Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a cylinder head for an internal combustion engine, and more specifically, to an improved durability of the valve bridge portion formed between the intake port and the exhaust port where intake/exhaust valves are installed. .

The valve bridge portion of the cylinder head is
Due to the mechanism of the intake and exhaust valves and the shape of the combustion chamber, it is not possible to make the gap between the intake and exhaust ports very wide, so even though the parts are weak in strength, they are heated by the combustion heat of each explosion. As high thermal stress is repeatedly generated due to cooling by intake air during the intake stroke, thermal fatigue is large, and there is a risk that cracks may form in this area.

In particular, this tendency increases in institutions that have achieved high output (HI-BMEP) in recent years.

For this reason, for example, as described in Japanese Utility Model Publication No. 48-25923, the cylinder head was reinforced by casting dissimilar metals and fusing them in the parts that required high strength when casting the cylinder head. There are some, but these have a complicated structure, require skill in the casting process, and are expensive.

The present invention was devised in view of the conventional situation, and has a structure in which the valve bridge part of the cylinder head is hardened in accordance with the thermal stress distribution that occurs during engine operation, and is simple and low-cost. It is an object of the present invention to provide a cylinder head for an internal combustion engine, which prevents the occurrence of cracks by increasing the durability and strength of a valve bridge portion through simple work.

The present invention will be explained below based on an embodiment shown in FIGS. 1 and 2.

FIG. 1 shows a cylinder head 1 viewed from the combustion chamber side, and shows a valve bridge portion 7 formed between an exhaust port 2 and an intake port 3 to which an exhaust valve and an intake valve (not shown) are installed, respectively. produces a thermal stress distribution as shown in FIG. 2 during engine operation. In addition, 4
5 is a valve guide mounting hole for the exhaust valve, 5 is a valve guide mounting hole for the intake valve, and 6 is a hole to which an injection nozzle or the like is mounted.

Here, in the present invention, hardening is performed in accordance with the thermal stress distribution shown in FIG. 2 above. To explain this in detail,
The approximately central part of the valve bridge part 7 on the exhaust port 2 side is exposed to combustion heat during the explosion stroke and is also blown with high-temperature exhaust gas during the exhaust stroke, and is also the thinnest part and therefore receives an extremely large thermal load. This produces the greatest thermal stress (A in Figure 2).
Thermal stress decreases as it moves away from this portion A, and as the gap between the intake and exhaust ports 2 and 3 and the gap between these and the injection nozzle mounting hole 6 increases beyond a certain level, the thermal stress becomes further weakened. This thermal stress distribution is calculated in advance based on the wall thickness, thermal load, etc. of each part of the valve bridge portion 7.

Therefore, for example, by using a carbon dioxide laser, the laser beam irradiation amount is increased to apply strong hardening to the parts that generate strong thermal stress, and as the thermal stress becomes weaker, the irradiation amount is decreased to weaken the hardening. (A, B, C, D in Figure 2).

Since the valve bridge portion 7 can be reinforced by hardening in this way,
It can withstand even severe engine operating conditions and improves the reliability of the cylinder head.
Further, as a result of increasing the strength of the valve bridge portion in this way, the wall thickness of the valve bridge portion can be reduced, and layout efficiency for mounting the valve is also improved.

Furthermore, if a laser is used, the valve bridge portion 7 can be
Hardening can be done in a short time by simply stroking the surface of the material, and since it is only necessary to irradiate as much as necessary according to the thermal stress distribution, there is no waste and it is advantageous in terms of cost. The thermal stress of the valve bridge is programmed, and the results are used to automatically harden the valve bridge.

In addition to laser hardening, induction hardening may also be used, and even in this case, the work is easier than the conventional method of casting dissimilar metals.

As explained above, according to the present invention, quenching is applied to only the locally weak valve bridge portion between the intake and exhaust ports of the cylinder head, with varying degrees of strength depending on the thermal stress distribution. This method has various advantages, such as being able to reliably reinforce the valve bridge portion with a simple operation, increasing the reliability of cylinder heads in high-output engines, and being advantageous in terms of cost.

[Brief explanation of the drawing]

FIG. 1 is a plan view of a main part of a cylinder head showing an embodiment of the present invention, and FIG. 2 is an enlarged view of the valve bridge portion of FIG. 1. 1... Cylinder head, 2... Exhaust port, 3...
Intake port, 7...Valve bridge part.

Claims (1)

[Scope of utility model registration request] An internal combustion engine characterized in that the valve bridge part formed between the intake port and the exhaust port, where the intake/exhaust valve is attached, is hardened to a degree corresponding to the strength of thermal stress generated during engine operation. Engine cylinder head.