Crankcase Separating Wall Thickness Gradient for Engine Output
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Solution Overview
Problem
Multiple-cylinder four-cycle engines face challenges in reducing friction resistance and pressure fluctuations due to the design of crank chambers, which limits engine output and complicates the casting process, especially in tight spaces like those found in motorcycle engines.
Innovation Solution
The design features a crankcase with a separating wall that increases in thickness from the joint surface to the deepest portion of the crank journal bearing hole and then decreases, allowing for increased internal volume and reduced friction resistance, along with a cut portion that facilitates fluid communication between crank chambers and simplifies flash removal during casting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If connecting holes are formed to extend over piston sliding surfaces inside cylinders and crankcase parts, then pumping loss is reduced, but friction resistance increases due to oil mist scattering
Solution Approach 1:
The patent applies local quality by creating a specific thickness distribution in the separating wall - thicker at the joint surface and thinner toward the cylinder side. This localized structural variation allows the wall to provide sufficient strength at the joint while creating a more favorable flow path in the crank chamber region, thereby reducing both pumping loss and friction resistance from oil mist scattering.
2Manufacturing precision
If a cylinder block having a closed deck structure is manufactured via sand casting, then roundness of cylinder inner diameter is improved, but manufacturing complexity and cost increase
Solution Approach 1:
The patent merges the cylinder block and crankcase into a single integrally cast component. By combining these two parts that were previously manufactured separately, the invention achieves the roundness benefits of closed-deck structure while simplifying manufacturing through a single die-casting process, thereby reducing overall manufacturing complexity and cost.
3Manufacturing precision
If the parting plane is positioned near the joint portion, then flash removal becomes difficult in narrow spaces, but casting precision is improved
Solution Approach 1:
The patent extracts the flash removal problem from the narrow joint space by positioning the parting plane away from the joint portion. This allows flash to be generated in an accessible location that can be easily removed, while the joint portion maintains its precise positioning through the thickened separating wall design that provides structural stability.
4Power
If separating wall thickness is reduced to increase crank chamber volume, then engine output increases, but structural strength decreases
Solution Approach 1:
The patent applies local quality by creating a non-uniform thickness distribution in the separating wall. The wall is thicker at the joint surface where structural strength is critical, and thinner toward the cylinder side where increased crank chamber volume benefits engine output. This localized variation resolves the contradiction between strength and power.
Solution Approach 2:
The patent introduces asymmetry in the separating wall thickness - the wall is not uniformly thick but rather has a gradient from the joint surface toward the cylinder side. This asymmetric design allows different regions of the wall to serve different functions: structural support where needed and volume expansion where beneficial for engine performance.
Data Source
AI summary
A crankcase for a multiple-cylinder four-cycle engine, including an upper crankcase and a lower crankcase which are joined to each other at a joint surface; a separating wall which is integrally cast with the upper crankcase and the lower crankcase to extend from the joint surface toward the opposite side of the joint surface and are configured to define crank chambers corresponding to adjacent cylinders; and a crank journal bearing hole which is formed on the separating wall and is configured to support a crankshaft. At least the separating wall formed in the upper crankcase has a thickness that increases from the joint surface of the crankcase to a region near a deepest portion of the crank journal bearing hole and decreases from the region near the deepest portion of the crank journal bearing hole toward the opposite side of the joint surface of the crankcase.