JP2004340130A - Cylinder head of reciprocating piston internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve surface properties of a cylinder head of a reciprocating piston internal combustion engine. <P>SOLUTION: A metal worked part of the cylinder head 2 of the reciprocating piston internal combustion engine is coated by employing a micro arc oxidation treatment. Ranges (gas exchange valves 7, 7', valve guides 8, 8', valve seat rings 9, 9') coated by employing the micro arc oxidation treatment are provided in the cylinder head 2 of the reciprocating piston internal combustion engine. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to the use of coating on metal workpieces for cylinder heads of reciprocating piston internal combustion engines. Known micro-arc oxidation treatments on light metals (also known as plasma arc or plasma electrolytic oxidation or micro-arc discharge oxidation) are used to improve the surface characteristics of the cylinder head of a reciprocating piston internal combustion engine. The present invention also relates to a cylinder head of a reciprocating piston type internal combustion engine having a region coated using a micro-arc oxidation treatment method, and a method of manufacturing a cylinder head.

  Modern reciprocating piston internal combustion engines comprise at least one cylinder that holds a piston that rotates a crankshaft via a connecting rod, a cylinder head that closes a combustion chamber formed by the piston and the cylinder at the top, Having. Cylinder heads typically include a plurality of gas exchange valves for intake and exhaust of combustion gases. The use of cylinder heads made of light metals or light metal alloys is part of the prior art. However, light metal cylinder heads have areas where light metal does not meet operating requirements. For example, the area used to direct the gas exchange valve is reinforced with a liner made of brass or a sintered alloy. The sealing surface of the gas exchange valve is also typically reinforced by a ring made of a hardened steel alloy known as a valve seat ring.

  Micro-arc oxidation treatments of light metals are known, for example, from US Pat. It is also known to use a micro-arc oxidation treatment to coat cylinders and pistons.

  Conditions required for the micro-arc oxidation treatment include an acidic or basic electrolyte bath containing a specific aqueous electrolyte solution in which one or more workpieces are immersed. The workpiece forms the anode, while the container forms the cathode. The voltage is applied to the workpiece, in this case a cylinder head, until a small arc is formed at a constant current density. After a period of time, this will be an oxidized surface layer, typically about 0.02-0.5 mm thick. This surface layer is characterized by greatly improved hardness, reduced friction and improved wear resistance. The outermost formed porous region is mechanically removed prior to first use.

Furthermore, the thermal conductivity of the oxide layer is greatly reduced compared to the original material, so that a certain heat shielding is obtained.
International Publication No. 00/05493 pamphlet U.S. Pat. No. 6,197,178 "Friction and wear characteristics of micro-arc oxidation coating for light weight, wear resistant, powertrain component application", SAE Paper, 1997. Year, 970022

  If micro-arc oxidation is applied to various areas of the cylinder head, various improvements can be obtained, such as, for example, improved heat insulation and abrasion resistance. Areas where the surface should not be oxidized must be covered while the process is used.

  It is therefore an object of the present invention to improve the cylinder head of a reciprocating piston internal combustion engine by using micro-arc oxidation of light metals so as to extend the product life and at the same time reduce the production costs.

  This object is achieved by using a method according to claim 1. According to the dependent claims, it is further advantageous.

  According to the invention, a cylinder head made of light metal for a reciprocating piston internal combustion engine is coated by the micro-arc oxidation treatment described above. As described above, the micro-arc oxidation process results in an oxidized surface layer having a thickness of about 0.02-0.05 mm. This surface layer has significantly different properties than the base material. For example, hardness is significantly improved, abrasion resistance is improved, and thermal conductivity is reduced. These properties can be used advantageously in cylinder heads with different purposes in different areas.

  Thus, according to the invention, the sealing surface of the cylinder head for the gas exchange valve is coated with a micro-arc coating. Some prior art uses light metal cylinder heads known as valve seal rings for these sealing surfaces. This is necessary because light metals cannot withstand long term loads that create an impact on the sealing surface when the gas exchange valve closes. Thus, the valve seat ring is usually made from hardened steel. As a result of the sealing surface being coated by using micro-arc oxidation, the sealing surface of the cylinder head is cured such that there is no need to use a valve seat ring. This reduces processing steps in the cylinder head and eliminates valve seat ring manufacturing and fitting steps. A further advantage of this configuration is that it is possible to configure the cylinder head such that the coating area is much thinner than the commonly used valve seat ring, and consequently the cooling water passage is closer to the valve. That's what it means.

  A further application of the micro-arc oxidation treatment in a cylinder head according to the invention is in the valve guide of a gas exchange valve. The light metal of the cylinder head usually does not meet the requirements that arise for sliding bearing guides. Thus, a guide liner made of alloy or sintered material is used to guide the gas exchange valve, which is usually made of steel. Such liners store certain emergency operating characteristics in the absence or sufficient supply of operating lubricant and / or store a small amount of lubricating oil to ensure such emergency operating characteristics. Provide a certain porosity. According to the present invention, if the guide of the gas exchange valve is machined directly from the light metal of the cylinder head and then coated using a micro-arc oxidation treatment, the guide characteristics of the gas exchange valve listed above are obtained, and the result is Thus, there is no need to use a separate guide liner.

  Furthermore, according to the invention, it is advantageous if the intake and exhaust ports of the cylinder head are covered using a micro-arc oxidation treatment. The intake / exhaust port refers to a passage that draws combustion air into the cylinder and discharges exhaust from the cylinder. As described above, the surface layer formed by the micro-arc oxidation treatment has a lower thermal conductivity than the light metal cylinder head. This thermal insulation is useful, albeit slightly, for the combustion air intake port. Because the fact that the combustion air is heated only slightly when the engine is hot is small, so the cooler the air, the higher its density, the better the filling rate of the cylinder with the combustion air. It is. Furthermore, it is also appropriate to cover the exhaust port. Adiabatic means that the exhaust is not cooled significantly and, consequently, that the exhaust purification catalyst normally connected downstream reaches the light-off temperature more quickly.

  A further advantageous configuration of the invention is to coat a web, called a valve web, between two valve seats in a cylinder head. This region is typically exposed to particularly high thermal stresses due to the thin walls between the exhaust and intake ports. It is advantageous to increase the thermal insulation of this area by coating this area with a micro-arc oxidation treatment.

  The invention is also applicable to cylinder heads having a coating generated using a micro-arc oxidation process in at least one of the above-mentioned regions.

  Furthermore, the invention proposes a treatment when the cylinder head is coated in at least one of the above-mentioned areas. Areas not to be covered are covered in a suitable manner. For example, depending on the specific requirements, one or more areas of the cylinder head or the entire cylinder head can be coated in a known manner.

  FIG. 1 is a partial sectional view of a reciprocating piston type internal combustion engine 1. This figure shows a cylinder head 2, a part 3 of a cylinder block, a cylinder 4, and a piston 5 movably arranged in the cylinder 4. The piston 5, together with the cylinder 4 and the cylinder head 2, forms a combustion chamber 6. The combustion air passes through one of the two gas exchange valves 7, 7 'and the intake port 10 and proceeds into the combustion chamber 6, while the exhaust gas passes through the other of the two gas exchange valves 7, 7' and the exhaust port 11. And exit the combustion chamber. The gas exchange valves 7, 7 'are usually configured to be movable in valve guides 8, 8'. Valve seat rings 9, 9 'on which the sealing surfaces of the gas exchange valves 7, 7' are formed are set in the cylinder head 2.

  According to the invention, a light metal cylinder head 2 is coated in the region of the sealing surfaces of the gas exchange valves 7, 7 'using a micro-arc oxidation method. In this area, gas exchange valves 7, 7 'hit the cylinder head at high speed when closed, so valve seat rings 9, 9' made of ordinary hardened steel have been commonly used. In contrast, if this area was coated by the micro-oxidation method as described above, the coating layer would meet that requirement and consequently omit the valve seat ring 9, 9 ' .

  The same applies to the area of the valve guides 8, 8 'in which the gas exchange valves 7, 7' are mounted. The light metal of the cylinder head 2 usually does not satisfy the requirements required for the bearings of the gas exchange valves 7, 7 '. The sliding bearing arrangement of the gas exchange valves 7, 7 'must not only have sufficient wear resistance, but also have emergency operating characteristics. This is because it takes one or two seconds for the lubricating oil to reach all the bearing positions when the internal combustion engine 1 is started. According to the invention, this bearing area of the gas exchange valves 7, 7 'is covered with an oxidized surface layer by micro-arc oxidation. This layer is sufficiently abrasion resistant and somewhat porous to retain a certain amount of oil, which makes the desired emergency operating characteristics. The individual valve guides 8, 8 'can then be arranged. It is also conceivable to add a coating of PTFE (Teflon) or a low friction lacquer.

  According to the present invention, it may be advantageous to cover the intake port 10 and / or the exhaust port 11 of the internal combustion engine 1. This coating has a lower thermal conductivity than the substrate. On the intake side, this means that the combustion gas is heated to a lesser extent, so that a lower temperature, denser combustion gas and thus more combustion gas can enter the combustion chamber 6. Advantageously, on the exhaust side, because of this thermal insulation, the exhaust does not cool down so quickly and, as a result, for example, the exhaust purification catalytic converter reaches its light-off temperature more quickly.

  Since the area of the valve web 12 is exposed to large temperature differences and significant mechanical loads, insulation in this area is also advantageous.

It is a partial sectional view of an internal combustion engine.

Explanation of reference numerals

1 Reciprocating piston internal combustion engine
2 cylinder head
7, 7 'gas exchange valve
10 Intake port
11 Exhaust port
12 Valve web

Claims (7)

  A method using a micro-arc oxidation treatment to coat a cylinder head (2) made of light metal of a reciprocating piston internal combustion engine (1).   2. The method as claimed in claim 1, wherein the cylinder head (2) is coated in the area (9, 9 ') where the disk of the gas exchange valve contacts.   2. The method as claimed in claim 1, wherein the cylinder head (2) is coated in the contact area (8, 8 ') of the guide of the gas exchange valve.   2. The method of claim 1, wherein the intake and exhaust ports (10, 11) are covered.   2. The method of claim 1, wherein the valve web (12) is coated.   A cylinder head for a reciprocating piston internal combustion engine coated by the method according to claim 1. A method for coating a cylinder head (2) for a reciprocating piston internal combustion engine (1) using a micro-arc oxidation method,
The method according to any one of claims 2 to 5, wherein the area other than the coated area is covered so that no surface coating is formed during the micro-arc treatment.

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