Crankcase Coating with Varying Pore Size
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Solution Overview
Problem
Crankcases made from die-cast Al-Si alloys in internal combustion engines face tribological stress issues due to high porosity and low wear resistance, necessitating the use of gray cast iron liners for stability, but these have limitations in corrosion resistance and friction losses.
Innovation Solution
A light metal crankcase with a coated cylinder surface featuring a varying pore size and proportion along its length, achieved through die-casting, fine turning, roughening, and applying a tribologically advantageous coating with controlled pore distribution and material composition, including unalloyed steel, to enhance wear resistance and lubrication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If gray cast iron liners are used in light metal crankcases, then tribological stability is improved, but corrosion resistance deteriorates and friction losses increase
Solution Approach 1:
The invention applies a porous coating layer on the cylinder surface with controlled pore size (0.5-500 μm) and pore area fraction (1-50%). The pores store lubricant and generate hydrodynamic pressure, improving tribological stability without using gray cast iron liners. This resolves the contradiction by achieving reliability through porous structure rather than through iron material properties.
Solution Approach 2:
The invention creates a composite structure consisting of a light metal substrate (Al-Si alloy) combined with a porous coating layer made of different materials. This composite approach allows the base material to provide corrosion resistance while the porous coating provides tribological stability, eliminating the need for gray cast iron liners.
2Productivity
If die-casting process is used for crankcase production, then manufacturing cost and productivity are improved, but porosity increases and wear resistance deteriorates
Solution Approach 1:
The invention applies preliminary surface preparation steps (fine turning and roughening) before applying the porous coating. The roughened surface provides anchoring for the coating, ensuring strong adhesion. This preliminary action allows the use of die-casting while compensating for its inherent porosity and low wear resistance through the subsequent coating layer.
Solution Approach 2:
The invention intentionally creates a porous coating layer with controlled pore characteristics that compensates for the porosity inherent in die-cast components. The porous structure stores lubricant and generates hydrodynamic pressure, providing wear protection that overrides the negative effects of die-casting porosity.
3Ease of manufacture
If hypoeutectic Al-Si alloys are used for die-casting, then ease of manufacture is improved, but tribological stressability deteriorates due to low strength and high ductility
Solution Approach 1:
The invention creates a composite system where the hypoeutectic Al-Si alloy provides ease of manufacture and the porous coating layer provides tribological strength. The coating material and structure compensate for the inherent weaknesses of the aluminum alloy, allowing the use of processable materials without sacrificing performance.
Solution Approach 2:
The porous coating layer with controlled pore size and distribution provides the tribological strength needed to withstand piston ring stresses. The pores store lubricant and generate hydrodynamic pressure, creating a load-bearing lubrication film that compensates for the low strength and high ductility of the hypoeutectic aluminum alloy.
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
The coated crankcase exhibits improved wear resistance, reduced friction losses, and enhanced corrosion resistance, allowing for reduced piston ring contact pressure and increased hydrodynamic friction, while eliminating the need for gray cast iron liners, offering a cost and weight advantage.
Implementation Method 1
The coating has a large number of pores, with the average size of the pores and/or the proportion of pores varying over the length of the cylinder
Implementation Method 2
the pores serve to 'store' the oil and form 'micro-pressure chambers' during engine operation
Implementation Method 3
Relevant prior art also includes the paper entitled 'Thermal spraying of cylinder bores with the Plasma Transferred Wire Arc process' by K. Bobzin, F. Ernst, K. Richardt, T. Schlaefer
Implementation Method 4
The size of the metal or alloy droplets that are sprayed onto the roughened inside of the cylinder is crucial for the formation of a tribologically advantageous surface layer
Data Source
Figure 1
AI summary
An internal-combustion engine has a crankcase, with at least one cylinder for accommodating a piston, the inner face of which cylinder is provided with a coating forming a running surface for the piston. The coating has a plurality of pores and the average size of the pores and/or the pore surface proportion varies over the length of the cylinder.