JPS618445A - Cylinder block in internal combustion engine - Google Patents

Abstract

PURPOSE:To form an appropriate quenched part in an optional part of a cylinder block to enhance the wear-resistance thereof, by forming a quenched part in the bore surface of the cylinder block in a suitable part excepting a part of having a cylinder block wall thickness which is less than a predetermined value from the core surface. CONSTITUTION:Cylinder bores 2 are formed in parallel with each other in a cylinder block 1, and cooling water passages 3 through 5 are formed in the outer peripheral large thickness wall parts of the cylinder block near to the cylinder bores 2. In this case, there is provided a laser beam irradiating device 8 composed of a laser generating head 9, reflecting mirrors 10, 10', a condensing lens 11, etc., and the irradiating port 14 of an irradiating part casing 13 in the device 18 is confronted to the internal diameter section of the bore 2. Further, a quenched part formed in the peripheral surface of the bore by this irradiating device 8 is provided in a suitable part thereof excepting a part having a cylinder block wall thickness less than a predetermined value from the bore surface. For example, it is formed each of sections l1-l2 ranging from the contact part between a piston ring at the top dead center of a piston and the outer surface of the bore 2 to a suitable descending level.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to the structure of a cylinder block for an internal combustion engine, in which an extremely thin hardened layer is formed by laser hardening on the surface layer of the bore of the cylinder block made of flake graphite cast iron. It is something.

[Conventional technology]

When a cylinder block for an internal combustion engine is made of flake graphite cast iron, the structure of the flake graphite cast iron consists of parts of pearlite or cementite where carbon exists in a combined state with iron, and a part where carbon exists in a free state as flake graphite. It has a non-uniform structure due to the parts that are formed, and the hardness as a whole is lower than that of steel, so it is easy to machine parts such as bores, and the cost of raw materials is low. Because the graphite part itself is soft and lubricating oil tends to accumulate in this part, it makes good contact with the surface of the piston ring, but since it has low wear resistance, the bore will wear out due to friction with the piston ring. It has a severe drawback of poor durability.

In order to improve durability, it is conceivable to put a liner on the inner surface of the bore or to plate it with Cr, but this would impair the usefulness due to the presence of flaky graphite and increase costs. Also, Ni+Cr, Mo and Cu.

Cast iron containing Cr, Sb, etc. increases the hardness of the entire cylinder, making it difficult to machine parts other than the bore after casting.

Therefore, in order to increase the hardness of only the bore part while maintaining the ease of machining of flake graphite cast iron and the good lubrication properties of flake graphite that exists in the structure in a free state, it is necessary to perform a poling process on the bore part. After that, it is conceivable that only the surface of the bore portion is surface hardened by induction hardening, flame hardening, or the like before honing. In these hardening methods,
The surface of the object must be heated and cooled over a wide range, such as by heating the surface of the object widely and uniformly, and then cooling it with water, a water-soluble quenching agent, oil, or the like.

On the other hand, research on hardening using laser beams (hereinafter referred to as laser hardening) has recently become active, and the results are published in "Research on Laser Hardening", Journal of the Welding Society, Vol. 50, No. 2, pp. 82-88. It has been announced.

The laser hardening method reduces the spot size of a laser beam and irradiates it onto the surface of an object such as steel at an appropriate moving speed, locally heating the surface, and after the laser beam passes, the heated surface is heated. Hardening takes advantage of the phenomenon in which a part is cooled by heat conduction to its surroundings, and the laser beam can be irradiated even on the complex surface of the object, so parts with complex shapes can be hardened locally with almost no thermal distortion. Can be hardened. - Also, the amount of heat input is much lower than that of conventional quenching methods.
Irradiation of thermal energy by a laser beam can be applied to only a part of the surface of the object, and can be limited to an extremely limited depth of the surface layer, and cooling can be performed by heat conduction to the surrounding area, which can be cooled with water or oil. It has features such as no process required.

[Problem that the invention seeks to solve]

However, when this laser hardening method is applied to harden the bore surface of a flaky graphite cast iron cylinder block of an internal combustion engine, the following problems arise.

As is well known, the temperature of the cylinder block reaches its highest on the cylinder head side due to the heat generated in the cylinder bore during internal combustion engine operation, which can cause seizure of the piston. In the cylinder block of an internal combustion engine, a cooling water passage is formed in the thick part of the outer periphery of the bore.

In the cylinder block of a multi-cylinder internal combustion engine, the wall thickness between adjacent bores is made as thin as possible in order to reduce size and weight, but the temperature rises rapidly between adjacent bores due to heat from both sides. In order to improve heat conduction from the bore, the wall thickness from the bore surface to the cooling water flow path wall surface is made as thin as possible.

Therefore, since the heat capacity of the thin-walled portion is small, that portion reaches the maximum temperature first during heating for the quenching, and
The outermost surface layer of the bore near that part enters a molten state, and during subsequent quenching and cooling, the cooling rate is significantly different from that of other parts, so quench cracking is particularly likely to occur in the thin-walled part due to thermal strain.

Moreover, the flake graphite part in the cylinder block made of flake graphite cast iron is non-metallic and is itself extremely weak, causing a type of crack to form in the other structure (pearlite) of the cast iron. Therefore, during quenching, a stress concentration phenomenon occurs around the flaky graphite part due to thermal stress, and a crack appears from the tip of the flaky graphite, which grows and causes so-called quench cracking, which leads to fracture. Therefore, as mentioned above, in areas where the wall thickness of the cylinder block is extremely thin, such as between the bore surface and the cooling water flow path, the outermost layer of the structure may melt, causing quench cracks in that area. There is a considerable risk of quenching, and the phenomenon of quenching cracking in the thin-walled portion is significant, and therefore, it has been considered impossible to quench the bore portion of a cylinder block made of flaky graphite cast iron.

c. Means for Solving Problems] The present inventor took advantage of the fact that in the laser hardening method, it is possible to partially harden the surface of the workpiece,
A laser beam irradiates the bore surface side of a thin walled part from the bore surface, such as the thick part between adjacent bores in a cylinder block made of flake graphite cast iron, or the space between the bore surface and the cooling water flow path. Place a shielding plate that is difficult to absorb (or do not apply a coating to improve the laser beam absorption rate)
Alternatively, by interrupting the laser beam irradiation and not laser hardening the bore surface facing the thin-walled part, and forming a hardened part by laser hardening on the other bore surface parts, an inexpensive and wear-resistant material can be obtained. To provide an excellent flaky graphite vP iron cylinder block.

[Effect]

In this way, among cylinder blocks made of flaky graphite cast iron,
By not forming a laser hardened part on the bore surface that faces the thin walled part, and by forming the laser hardened part only on the thick walled part on the cylinder block bore surface, the thermal energy from the laser beam is transferred to areas with small heat capacity. Since there is no heat applied to the area, the area does not become overheated,
Therefore, the bore surface layer in that area will not melt and quench cracking will never occur. In addition, even in other thick-walled parts, laser hardening will prevent quench cracks from occurring in the outermost surface layer of the bore (only at the very shallow depth of the surface layer), at necessary locations on the cylinder block bore surface that are subject to severe wear. By forming a hardened part with a mixed structure of a highly hard cast iron structure and a free graphite flake, it is possible to improve wear resistance, and to achieve good machinability at low cost.

〔Example〕

Examples of the present invention will be described below. In the figure,
Reference numeral 1 indicates a multi-cylinder cylinder block made of flaky graphite cast iron for an internal combustion engine.In the cylinder block 1, cylinder bores 2 are lined up in series at appropriate intervals. A cooling water flow path of an appropriate shape of 3° 4.5° is bored in the thick portion. The wall thickness between the side wall of the cooling water flow path 5 and the surface 7 of each bore 2 in the thick wall section 6 between the adjacent bores 2 and 2 is extremely thin, about 2 degrees thick at the point where both are closest. It is something.

On the other hand, the laser beam irradiation device 8 is composed of a laser emitting head 9 for CO2, etc., a reflecting mirror 10, 10', a condensing lens 11, etc. Place the irradiation device 8 facing the inner diameter of the bore 2 of the cylinder block 1, and
Alternatively, the cylinder block 1 placed on a table (not shown) may be configured to be rotatable and vertically movable around the 2nd axis of its bore. Thus, the speed at which the laser beam 12 travels over the surface 7 of the bore 2 can be adjusted.

Furthermore, the focal length of the condensing lens 11 in the laser beam irradiation device 8 can be adjusted to adjust the size of the spot diameter on the bore surface 7 of the laser beam 12.
By slowing down the movement speed of the bore surface 7, the hardening depth can be adjusted during hardening in a direction substantially perpendicular to the direction of movement of the laser beam 12 relative to the bore surface 7.

The hardened portion 15 formed on the circumferential surface of the bore 2 of the cylinder block 1 made of flaky graphite cast iron in the present invention is a necessary portion that is subject to severe wear due to contact with the piston ring, for example, the piston ring at the top dead center of the piston. Dimensions (ρ1) to (7!2) downward from the two-line surface of the cylinder block 1 corresponding to the point of contact with the bore surface to the appropriate lowered position.
) is applied to the upper and lower areas.

Reference numeral 16 indicates a thin wall portion 6 between adjacent bores 2 in the thick wall portion of the cylinder block 1, where both the side wall of the cooling water passage 5 and the surface 7 of each bore 2 are closest to each other. Bore surface 7 where the wall thickness is extremely thin, such as
In order to form the non-hardened portion 16, in the illustrated embodiment, a shielding plate 17 having an arcuate shape or the like is temporarily bonded to the front surface of the shielding plate 17.

Further, the bore surface 7 other than the shielding plate was previously subjected to a zinc phosphate coating treatment, and then was irradiated with a laser beam.

This is because the shiny surface of metal reflects most of the laser beam, but coating with zinc phosphate increases the absorption rate of the laser beam and improves the hardening effect.

After this, when the spot portion of the laser beam 12 is moved and irradiated onto the bore surface 7 while rotating the irradiation device 8 or rotating the cylinder block 1, the bore surface 7 is irradiated except for the back surface of the shielding plate 17. The hardened portion 15 can be formed in the hardened portion 15.

As a result of irradiation while changing the diameter of the spot portion and its moving speed, it was found that if the hardening depth was 0.35 mm or less, a molten region could not be formed in the outermost surface layer of the bore even by laser hardening. No quench cracking occurred.

Maximum depth of hardened layer in hardened part: 0.35mff1
By making it about 1 mm, it is possible to sufficiently cope with the wear limit of the bore, Q, 1 mm, and improve the durability of the cylinder block.

The structure of the quenched part is uniform martensite,
It has a mixed structure with free flaky lead as it was cast, and the martensitic structure is very hard and has excellent wear resistance, while the flaky graphite part makes good contact with the piston ring. Also, the wettability was good.

In addition, in forming the non-hardened portion 16, instead of contacting the shielding plate 17, the application of the laser beam absorber may be omitted at only seven locations on the bore surface corresponding to the non-hardened portion 16, or The irradiation of the laser beam 12 may be interrupted only at that location by temporarily closing the shank 18 or the like.

〔Effect of the invention〕

In this way, according to the present invention, it is only necessary to move the laser beam while irradiating the bore surface, so that rapid heating and cooling can be applied only to a thin surface layer on a limited predetermined portion of the bore surface. The hardened portion can be formed in any surface shape over any range. Unlike conventional induction hardening, there is no need to harden a wide range of the surface of the bore including unnecessary parts, and there is no need for water cooling, etc., improving efficiency.

By appropriately changing the diameter of the laser beam spot and its moving speed, the maximum heating temperature of the hardened part of the bore surface can be adjusted.
The heating and cooling speed can be adjusted, and the quenching width and quenching depth can be controlled, and it is also possible to easily adjust the heating of the surface layer to the extent that the outermost layer does not melt, and also to make fine adjustments. .

Furthermore, in the part of the cylinder block where the wall thickness between the bore surface and the bore surface is extremely thin, there is no heat input by the laser beam, so there is no thermal strain or melting in the thin wall part due to overheating. Since quenching cracks do not occur on the surface layer of the bore, product defects due to quenching do not occur.

On the other hand, the structure in the quenched part is a mixed structure of flaky graphite and uniform martensite, which has excellent wear resistance, and the presence of flaky graphite makes contact with the piston ring smooth and inhibits lubricity. However, in areas other than the hardened part, it has the advantages of flake graphite cast iron, such as excellent machinability and low raw material costs.

Moreover, compared to a method in which a liner is stretched on the inner surface of the bore without quenching, the raw material and manufacturing costs can be significantly reduced, and the side wall of the cylinder block between adjacent bores can be reduced by the thickness of the liner. The thickness can be reduced, and the entire cylinder block can be made smaller and lighter.

[Brief explanation of drawings]

The drawings show an embodiment of the present invention, and FIG. 1 is a plan view of a cylinder block, FIG. 2 is a schematic diagram of a laser beam irradiation device, and FIG. 3 is an enlarged sectional view taken along line mm in FIG. 2. . 1... Cylinder block, 2... Bore, 7...
...Bore surface, 3, 4.5... Cooling water flow path, 6...
・・Thin wall part, 8・・・Laser beam irradiation device, 9・・・
...Laser oscillation head, 10.10'...Reflector,
11...Condensing lens, 12...Laser beam, 1
5...Quenched portion, 16...Non-quenched portion, 17.
...shielding plate, 18...shutter.

Claims (1)

[Claims] (1) The hardened part formed by moving laser beam irradiation on the bore surface of the cylinder block made of flaky graphite cast iron in an internal combustion engine, excluding the thin wall part where the wall thickness of the cylinder block from the bore surface is below a certain level. A cylinder block for an internal combustion engine characterized by being provided at appropriate locations.