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Research Papers: Gas Turbines: Microturbines and Small Turbomachinery

Oil-Free Automotive Turbochargers: Drag Friction and On-Engine Performance Comparisons to Oil-Lubricated Commercial Turbochargers

[+] Author and Article Information
Keun Ryu

Assistant Professor
Department of Mechanical Engineering,
Hanyang University,
Ansan, Gyeonggi-do 15588, South Korea
e-mail: kryu@hanyang.ac.kr

Zachary Ashton

Global Engineering Core Science,
BorgWarner Turbo Systems,
Arden, NC 28704
e-mail: zashton@borgwarner.com

Contributed by the Vehicular and Small Turbomachines Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 1, 2016; final manuscript received July 4, 2016; published online September 27, 2016. Editor: David Wisler.

J. Eng. Gas Turbines Power 139(3), 032301 (Sep 27, 2016) (10 pages) Paper No: GTP-16-1301; doi: 10.1115/1.4034359 History: Received July 01, 2016; Revised July 04, 2016

Oil-free bearings for automotive turbochargers (TCs) offer unique advantages eliminating oil-related catastrophic TC failures (oil coking, severe bearing wear/seizure, and significant oil leakage, for example), while increasing overall system reliability and reducing maintenance costs. The main objective of the current investigation is to advance the technology of the gas foil bearings (GFBs) for automotive TCs by demonstrating their reliability, durability, and static/dynamic force characteristics desirable in extreme speed and temperature conditions. The paper compares drag friction and on-engine performances of an oil-free TC supported on GFBs against an oil-lubricated commercial production TC with identical compressor and turbine wheels. Extensive coastdown and fast acceleration TC rotor speed tests are conducted in a cold air-driven high-speed test cell. Rotor speed coastdown tests demonstrate that the differences in the identified rotational viscous drag coefficients and drag torques between the oil-free and production TCs are quite similar. In addition, rotor acceleration tests show that the acceleration torque of the oil-free TC rotor, when airborne, is larger than the production TC rotor due to the large mass and moment of inertia of the oil-free TC rotor even though air has lower viscosity than the TC lubricant oil. Separate experiments of the oil-free TC installed on a diesel engine demonstrate the reliable dynamic-forced performance and superior rotor dynamic stability of the oil-free TC over the oil-lubricated TC. The post on-engine test inspection of the oil-free TC test hardware reveals no evidence of significant surface wear between the rotor and bearings, as well as no dimensional changes in the rotor outer surfaces and bearing top foil inner surfaces. The present experimental characterization and verified robustness of the oil-free TC system continue to extend the GFB knowledge database.

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Figures

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Fig. 1

Oil-free turbocharger supported on GFBs. (a) Photograph of assembled TC core and (b) cross-sectional schematic view (not to scale).

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Fig. 2

CAD models of oil-free TC rotor (top) and production TC rotor (bottom). CW diameter = ∼55 mm and TW diameter = ∼50 mm.

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Fig. 3

Production and oil-free TCs in cold air-driven test cell. Coastdown tests: recorded coastdown speed versus time. Two oil (SAE10W30) temperatures (57 °C and 87 °C) for production TC. Ωmax = top speed = ∼100 krpm. Inset figure shows speed ratio in logarithmic scale.

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Fig. 4

Production TC in cold air-driven test cell. Coastdown tests. Waterfall plot of BH accelerations along vertical plane: (a) Oil (SAE10W30) temperature = 87 °C. (b) Oil (SAE10W30) temperature = 57 °C. Ωmax = top speed = ∼100 krpm.

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Fig. 5

Oil-free TC in cold air-driven test cell. Coastdown tests: (a) waterfall of BH vertical acceleration and (b) waterfall of shaft motion amplitude measured at compressor end nose, vertical plane.

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Fig. 6

Production and oil-free TCs in cold air-driven test cell. Coastdown tests: (a) ∂Ω/∂t versus rotor speed ratio and (b) ct = Ip×(∂Ω/∂t)/Ω versus rotor speed ratio.

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Fig. 7

Production and oil-free TCs in cold air-driven test cell. Coastdown tests: drag torque (Tdrag = ctΩ) versus rotor speed ratio.

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Fig. 8

Production and oil-free TCs in cold air-driven test cell. Rapid acceleration tests: recorded coastdown speed versus time. Two oil (SAE10W30) temperatures (57 °C and 87 °C) for production TC. Ωmax = top speed = ∼100 krpm.

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Fig. 9

Production and oil-free TCs in cold air-driven test cell. Rapid acceleration tests: ∂Ω/∂t versus rotor speed ratio.

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Fig. 10

Production and oil-free TCs in cold air-driven test cell. Rapid acceleration tests: acceleration torque TAccel = Ip×(∂Ω/∂t) versus rotor speed ratio.

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Fig. 18

Post on-engine test conditions of heat shield (left) and turbine wheel (right)

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Fig. 17

Post on-engine test condition of oil-free TC rotor surface. No postcleaning conducted.

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Fig. 16

On-engine tests: recorded turbine inlet air, journal and thrust bearing temperatures versus elapsed test time with rotor spinning from 60 krpm to 100 krpm. BH coolant (5 °C) flow rate ∼210 g/s. Inset figure shows the measured temperature locations.

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Fig. 12

Waterfall of typical diesel engine acceleration test data below 300 Hz. Engine torque = 100 N·m along the vertical direction (Y-direction in Fig. 11). Engine speed changes from 1 krpm to 1.5 krpm while TC rotor speed changes from ∼60 krpm to ∼100 krpm (ramp rate: 40 kpm/min). e represents orders (multiples) of main engine speed.

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Fig. 11

On-engine test setup: (a) view from CW side and (b) view from TW side. Two triaxial accelerometers (one on the TC and the other on the engine) are shown. Orientation of each acceleration shown in inset figures.

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Fig. 15

On-engine tests. Amplitudes of synchronous (1X) and subsynchronous (sub-1X) vibrations versus rotor speed: (a) BH acceleration of production TC (SAE15W40 lubricated) along Y-direction (+135 deg) in Fig. 11. (b) BH acceleration of oil-free TC along Y-direction (+135 deg) in Fig. 11. (c) Shaft motion amplitude of oil-free TC measured at compressor end nose, vertical plane.

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Fig. 14

On-engine tests. Waterfall of below 300 Hz taken from Fig. 13: (a) BH acceleration of production TC (SAE15W40 lubricated) along Y-direction (+135 deg) in Fig. 11. (b) BH acceleration of oil-free TC along Y-direction (+135 deg) in Fig. 11. (c) Shaft motion amplitude of oil-free TC measured at compressor end nose, vertical plane. e represents orders (multiples) of main engine speed.

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Fig. 13

On-engine tests: (a) waterfall of acceleration on production TC (SAE15W40 lubricated) BH outer surface along Y-direction (+135 deg) in Fig. 11. (b) Waterfall of acceleration on oil-free TC BH outer surface along Y-direction (+135 deg) in Fig. 11. (c) Waterfall of shaft motion amplitude of oil-free TC measured at compressor end nose, vertical plane.

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