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240 Landmarks TopProduction > Ceramic turbocharger
 Ceramic turbocharger
Research and development of gas turbines progressed as a promising alternative to reciprocating engines. Especially in terms of thermal efficiency improvement, high temperatures are required at the inlet of the turbine, and the use of ceramics was studied as a heat resistant material. This technology was then applied to turbochargers for passenger cars to improve turbo lag.
Compared to a gas turbine, the temperature of a turbocharger is low at 1200 K, thus silicon nitride which is high in fracture toughness and strength was selected. Similarly to the gas turbine, its blade link portion and shaft portion are molded separately and integrated. Its manufacturing method uses gas pressure sintering, and a rotor of high strength was obtained by shape optimization using 3D finite element analysis. The rotor was designed differently from metallic rotors as follows.
1) It had a tapered shape from the backboard to the shaft
2) The connecting shape from the backboard to the shaft
3) Wall thickness distribution from the blade edge to the root
4) Hub shapes on the exducer side
5) Wall thickness shape of the blades
A metallic shaft was used for the shaft in consideration of strength and manufacturing costs. It is technically difficult to join heterogeneous materials which are remarkably different in basic composition and thermal expansion coefficients. Various joining methods were studied in view of the joining position, required strength, and heat resistance. Consequently, brazing and interference fit were selected for joining the high temperature portion, which less affects the engine when the shaft bends.
Hot spin tests were conducted for the turbocharger, and a constant for crack propagation speed was obtained based on the slow crack growth theory to estimate life. Strength and load largely affect life. Strength can be obtained by a function of the length of initial defects. Breaking stress equivalent to the length of the largest defect was obtained and stress equivalent to the breaking stress was applied to the rotor. The length of defect remaining in the rotor was below the maximum allowable defect length. Based on this idea, proof tests were conducted to ensure quality.
The rotational inertia moment of the rotor assembly was reduced by about 34%, and the time required for the turbocharger to reach 0 to 100,000 rpm was shortened by about 36%.
Storage location:NISSAN MOTOR CO., LTD., VEHICLE ADVANCED DEVELOPMENT DEPT. (560-2, Okatsukoku, Atsugi-shi, Kanagawa 243-0126)
Year manufactured:1985
Manufacturer:Nissan Motor Corporation
Classification:Other (literature)
Current status:In storage: not open to the public
Company name:Nissan Motor Corporation
Familiar name:Ceramic turbocharger
Installation vehicle:Fairlady Z
Year of manufacture:1985
Structure, type, measure, means, etc.:The silicon nitride ceramic turbo rotors were sintered after injection molding, and joined with a metallic shaft by brazing and interference fitting. The turbocharger's life was assured by applying a load equivalent to the maximum allowable defect length and selecting the remaining rotor.
Function, effect, etc.:Ceramic, which is a brittle material with half the specific gravity of heat resistant steel or less was used for a rotor as a lightweight material with excellent high temperature strength. The rotor was joined with a metallic shaft, and the rotational inertia moment was reduced. The transient state delay (turbo lag on acceleration) was reduced, which is one goal in the development of turbochargers.
Effect:Rotational inertia moment was reduced by about 2/3. Acceleration response was improved.
Reference materials:・Nissan Technical Review, Vol. 21, pp. 125-134, 1985
・SAE Paper 861128
・ Proceedings of the 14th Gas Turbine Society of Japan Congress
・The Japan Society of Mechanical Engineers, Hokuriku District Meeting
・Japan Society for the Promotion of Science, The 124th Committee for High Temperature Ceramic Material, The 136th Committee for Future Machining Technology, etc.
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