Boreless Hub Two-Stage Turbocharger Compressor
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Solution Overview
Problem
Conventional turbocharger designs face material property limits and efficiency issues at high pressure ratios, particularly in commercial diesel engines, due to high rotational speeds and the need for high-temperature materials like titanium for second-stage impellers, while conventional aluminum materials for first-stage impellers have shorter service lives.
Innovation Solution
A 'boreless' hub configuration with a triple-piloting arrangement for a two-stage serial compressor and shaft assembly, allowing for a coaxial relationship between impellers and the shaft without constraining axial movement, enabling the use of aluminum for the first-stage impeller and titanium for the second-stage impeller, thus improving concentricity and manufacturability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If high rotational speeds are used to achieve increased pressure ratios, then pressure ratio capability is improved, but material property limits are exceeded due to stresses in rotating components
Solution Approach 1:
The compressor is divided into two separate stages with two impellers mounted on the same shaft. The first-stage impeller handles lower pressure ratios using aluminum alloy, while the second-stage impeller handles higher pressure ratios using titanium alloy. This segmentation allows each component to operate within its material strength limits while achieving the overall high pressure ratio requirement.
Solution Approach 2:
Different materials are used for different components based on their local stress requirements. The first-stage impeller uses aluminum alloy where stresses are lower, while the second-stage impeller uses titanium alloy where stresses are higher. This local quality approach optimizes the strength-to-weight ratio and extends service life across the entire compressor system.
2Ease of manufacture
If conventional aluminum material is used for first-stage impeller, then ease of manufacture is improved, but service life is reduced compared to titanium second-stage impeller
Solution Approach 1:
The patent applies different materials to different stages based on their specific requirements. The first-stage impeller uses aluminum alloy for ease of manufacture and lower cost, while the second-stage impeller uses titanium alloy for extended service life and higher strength. The boreless hub configuration with proper piloting ensures both materials can be manufactured and assembled effectively.
3Stress or pressure
If two-stage serial compressor is used to achieve pressure ratios of 5 or greater, then pressure ratio capability is improved, but temperature of second-stage impeller is raised requiring high-temperature materials
Solution Approach 1:
The second-stage impeller is specifically designed with titanium alloy material that can withstand the elevated temperatures generated during high pressure ratio compression. This local quality approach ensures the hot zone of the compressor can operate at higher temperatures while the first-stage impeller continues to use aluminum alloy for its temperature range.
4Device complexity
If single-stage compressor design is used, then device complexity is reduced, but pressure ratio capability is limited to 3.5-4.0
Solution Approach 1:
The compressor is segmented into two stages with two impellers on a common shaft, allowing the system to achieve pressure ratios of 5 or greater. While this increases device complexity compared to a single-stage design, it enables the turbocharger to meet the elevated pressure ratio requirements of commercial diesel engines without exceeding material property limits.
Data Source
AI summary
A turbocharger with a two-stage compressor having first- and second-stage impellers mounted on a common shaft in a back-to-back configuration. The first-stage impeller has a boreless configuration, defining an unthreaded pilot hole receiving an unthreaded end of the shaft so as to establish a coaxial relationship between the impeller and the shaft. The first impeller further defines a hollow cylindrical pilot member that projects from the back of the impeller and is received in a portion of the bore through the second-stage impeller to position the impellers coaxially with each other. The shaft passes through the pilot member and is externally threaded for engaging threads on the inner surface of the pilot member to secure the impellers to the shaft. The bore of the second impeller has a second portion that engages an outer cylindrical surface of the shaft to establish a coaxial relationship between the shaft and impeller.