Cylinder Head Padding for Tensile Stress Suppression

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Solution Overview

Problem

In reciprocating engines, increasing the compression ratio leads to higher in-cylinder pressure, causing uneven deformation and tensile stress on the cylinder head, which can result in cracking or breakage due to differences in rigidity between the combustion surface and the circumferential edges of intake/exhaust ports.

Innovation Solution

A cylinder head design featuring an annular outer circumferential wall with a padding portion that increases thickness towards the port wall portions, reducing the distance between them and enhancing the rigidity of the bottom wall portion, while maintaining a balanced weight distribution and curvature to manage tensile stress effectively.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If the compression ratio is increased to achieve high efficiency, then the in-cylinder pressure increases and power output improves, but the tensile stress on the cylinder head increases and breakage probability increases

Engineering Contradiction:

Improvepower outputVSAvoidbreakage probability

Core Design Contradiction:

PowerVSReliability

Solution Approach 1:

The patent applies local quality by creating a padding portion with increased thickness at specific locations on the outer circumferential wall portion, particularly near the port wall portions. This localized reinforcement increases rigidity where tensile stress concentrates, allowing the cylinder head to withstand higher in-cylinder pressures without breaking while maintaining the overall lightweight design.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent utilizes curvature by forming the padding portion with a specific curved surface that satisfies certain radius relationships. This curved geometry helps distribute stress more evenly across the bottom wall portion while maintaining the padding effect, preventing stress concentration that would lead to cracking under high compression ratio conditions.

Inventive Principle:

Principle #14Spheroidality (Curvature)

2Strength

If the thickness of the outer circumferential wall portion is increased to improve rigidity, then the bottom wall portion becomes harder to bend and tensile stress is suppressed, but the weight of the cylinder head increases

Engineering Contradiction:

Improverigidity of bottom wall portionVSAvoidweight of cylinder head

Core Design Contradiction:

StrengthVSWeight of stationary object

Solution Approach 1:

Instead of uniformly increasing the thickness of the outer circumferential wall portion, the patent applies local quality by creating a padding portion only in specific regions where rigidity is most needed - namely near the port wall portions. This localized approach provides the necessary strength enhancement while minimizing the overall weight increase that would result from uniform thickening.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent applies partial action by providing padding only in the portions of the outer circumferential wall that are closest to the port wall portions, rather than excessively thickening the entire wall. This partial reinforcement is sufficient to suppress tensile stress in the critical areas while avoiding unnecessary material usage and weight gain in regions where full reinforcement is not required.

Inventive Principle:

Principle #16Partial or excessive action

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 design effectively suppresses tensile stress on the cylinder head's bottom wall, reducing the likelihood of breakage and allowing for increased in-cylinder pressure without size increments, thereby achieving high efficiency and output.

Implementation Method 1

a water chamber through which cooling water flows may be formed around intake/exhaust ports of the cylinder head or the like to alleviate the thermal stress and the thermal distortion of the cylinder head

Methodology Applied

Scientific EffectCooling: Cooling

Implementation Method 2

the outer circumferential wall portion includes a padding portion of which a thickness is increased toward a side close to the port wall portions so that a distance between the port wall portions and the outer circumferential wall portion is equal to or less than a predetermined distance

Methodology Applied

Scientific EffectStructural reinforcement:

Implementation Method 3

tensile stress acts on the bottom wall portion of the cylinder head according to the difference in the amount of deformation. That is, as the in-cylinder pressure is increased, the probability of breakage such as cracking occurring in the cylinder head is increased

Methodology Applied

Scientific EffectStress resistance:

Data Source

PatentUS10519895B2Cylinder head and engine

Publication Date: 2019.12.31 MITSUBISHI HEAVY IND ENGINE & TURBOCHARGER LTD

AI summary

The cylinder head includes a plurality of port wall portions configured to form flow paths for intake and exhaust, an outer circumferential wall portion formed in an annular shape disposed at an interval on an outside of the plurality of port wall portions and having a water chamber through which cooling water flows and which is formed at least between the port wall portions and the outer circumferential wall portion, and a bottom wall portion configured to face a combustion chamber of an engine and to connect ends of the port wall portions and the outer circumferential wall portion, wherein the outer circumferential wall portion includes a padding portion of which a thickness is increased toward a side close to the port wall portions so that a distance between the port wall portions and the outer circumferential wall portion is equal to or less than a predetermined distance.