Piston Anodizing via High-Purity Aluminum Coating

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Solution Overview

Problem

In direct injection engines, the additives in aluminum alloy pistons inhibit the formation of a smooth anodic oxide coating, leading to increased heat transfer and reduced combustion efficiency, and the sealing coatings applied to mitigate this are prone to damage from high-pressure fuel injection, potentially causing engine performance issues.

Innovation Solution

A method involving an aluminum coating with 99.0% purity or more is applied to the piston surface, followed by anodizing treatment to form a smooth anodic oxide coating, and a sealing coating is applied only on the outer side to prevent damage from fuel injection, while avoiding the inner side anodization to minimize surface irregularities.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Temperature

If anodizing treatment is performed on aluminum alloy piston top face, then heat shielding property is improved, but surface irregularities occur due to additives in the alloy

Engineering Contradiction:

Improveheat shielding propertyVSAvoidsurface smoothness

Core Design Contradiction:

TemperatureVSManufacturing precision

Solution Approach 1:

The patent extracts the harmful additives (silicon, magnesium, zinc) from the aluminum alloy composition to eliminate surface irregularities during anodizing. By using high-purity aluminum (99.0% or more) free from these additives, the anodic oxide coating forms smoothly without pores or irregularities, resolving the contradiction between heat shielding and surface smoothness.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent changes the chemical composition parameter of the aluminum alloy by specifying purity of 99.0% or more and explicitly excluding certain additives. This parameter change enables the anodic oxide coating to form with desired smoothness while maintaining the heat shielding function, thereby resolving the technical contradiction.

Inventive Principle:

Principle #35Parameter changes

2Ease of operation

If sealing coating is applied to cover surface irregularities, then flame fluidity is maintained, but the coating is damaged by high-pressure fuel injection

Engineering Contradiction:

Improveflame fluidityVSAvoidcoating durability

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The patent removes the sealing coating layer entirely by using high-purity aluminum that forms a smooth anodic oxide coating without irregularities. This eliminates the need for additional sealing coating that would be damaged by fuel injection, while still maintaining flame fluidity through the naturally smooth surface.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent replaces the durable but fragile sealing coating with a inherently durable smooth anodic oxide coating formed directly from high-purity aluminum. This eliminates the need for protective sealing layers that are vulnerable to fuel injection damage, achieving both durability and flame fluidity.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

3Strength

If conventional aluminum alloy is used for piston, then mechanical properties are improved, but anodic oxide coating formation is inhibited

Engineering Contradiction:

Improvemechanical propertiesVSAvoidcoating uniformity

Core Design Contradiction:

StrengthVSManufacturing precision

Solution Approach 1:

The patent applies different aluminum purity requirements to different parts of the piston: the piston body uses conventional aluminum alloy (AC8A or AC8B) for mechanical strength, while the piston top face uses high-purity aluminum (99.0% or more) for smooth anodic oxide coating formation. This local differentiation resolves the contradiction between mechanical properties and coating uniformity.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent segments the piston into two functional zones with different material requirements: the skirt portion uses conventional alloy for strength and durability, while the top face uses high-purity aluminum for optimal anodizing performance. This segmentation allows each region to have the properties needed for its specific function.

Inventive Principle:

Principle #1Segmentation

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This approach suppresses the occurrence of damage to the sealing coating, maintains combustion efficiency by reducing flame fluidity issues, and prevents engine performance deterioration by ensuring the anodic oxide coating remains smooth and intact.

Implementation Method 1

forming an anodic oxide coating having pores over an entire area of a top face of the piston by subjecting the top face of the piston to an anodizing treatment

Methodology Applied

Scientific EffectAnodizing: Anodising

Implementation Method 2

forming an aluminum coating having an aluminum purity of 99.0% or more over an entire area of a surface of the cavity portion

Methodology Applied

Scientific EffectPhysical vapor deposition: Physical Vapour Deposition

Data Source

PatentUS9932929B2Method for manufacturing piston for direct injection engine

Publication Date: 2018.04.03 TOYOTA JIDOSHA KK

AI summary

A piston for a diesel engine is prepared as a piston for a direct injection engine, a cavity face of the piston is grinded, and a squish face thereof is masked. Next, a high-purity aluminum coating is formed on the cavity face, and the masking of the squish face is removed and the entire area of the piston top face is subjected to an anodizing treatment. Thereafter, the cavity face is masked, and the squish face is subjected to a sealing treatment.