Turbocharger Rotor Shaft Rigidity Tuning for Critical Speed Vibration
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Solution Overview
Problem
The increasing high-speed rotation of forced induction devices leads to a higher likelihood of vibration in the rotor, particularly in the high rotational speed region, as the secondary critical speed approaches the maximum rotational speed, resulting in potential vibration issues.
Innovation Solution
The forced induction device incorporates a connection shaft with lower rigidity than the turbine and compressor shafts, positioned between the turbine and compressor bearings, to minimize vibration by locating the node of the mode shape between these bearings, and employs design features such as smaller diameter, rounded connections, and potentially hollow or alternating high-low rigidity sections to reduce stress concentration and enhance durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the forced induction device operates at high rotational speeds to improve output, then productivity is improved, but vibration occurs in the rotor when the secondary critical speed approaches the maximum rotational speed
Solution Approach 1:
The connection shaft portion is designed with different rigidity characteristics compared to the turbine and compressor shaft portions. Specifically, the connection shaft portion has lower rigidity to create a node in the mode shape at critical speeds, while the turbine and compressor shaft portions maintain higher rigidity for structural integrity. This local differentiation of mechanical properties allows the system to operate at high speeds while suppressing vibration through strategic placement of the vibration node between the bearings.
2Object-affected harmful factors
If the rigidity of the connection shaft portion is reduced to locate the vibration node between bearings, then vibration response is suppressed, but the structural strength may be compromised
Solution Approach 1:
The rigidity parameter of the connection shaft portion is specifically adjusted to be lower than that of the turbine and compressor shaft portions. This parameter change is achieved through design modifications such as reducing the diameter or changing the cross-sectional geometry of the connection shaft portion. The rigidity is optimized to create a node in the mode shape at critical speeds, suppressing vibration while maintaining sufficient structural strength through careful parameter selection.
Solution Approach 2:
Rounded portions are provided at the connection regions between the connection shaft portion and the turbine/compressor shaft portions. These curved transitions eliminate sharp corners and stress concentration points, allowing the connection shaft portion to have reduced rigidity without compromising structural integrity. The curvature distributes stress more evenly, preventing local stress concentration that would otherwise occur at sharp transitions.
Data Source
AI summary
A forced induction device (100) includes: a rotor (1) which includes a turbine side shaft portion (11), a compressor side shaft portion (12), and a connection shaft portion (13) connecting these to each other; a turbine side bearing (5) which supports the turbine side shaft portion (11); and a compressor side bearing (6) which supports the compressor side shaft portion (12). A rigidity of the connection shaft portion (13) is lower than that of the turbine side shaft portion (11) and the compressor side shaft portion (12) so that a node in a mode shape at each critical speed involving with an operating rotational speed region of the rotor (1) is located between the turbine side bearing (5) and the compressor side bearing (6).