Feasibility Study of an Oil Free Turbocharger Supported on Gas Foil Bearings Via On Road Tests of a Two Liter Class Diesel Vehicle

Abstract

This paper presents the feasibility study of an oilfree turbocharger (TC) supported on gas foil bearings (GFBs) via onroad tests of a 2liter class diesel vehicle. The oilfree TC is constructed using a hollow rotor with a radial turbine at one end and a compressor impeller at the other end, a center housing with journal and thrust GFBs, and turbine and compressor casings. The oilfree TC reuses parts of a commercial variable geometry turbocharger, except for the rotorbearing system. In a test rig driven by a diesel vehicle engine (EG), the rotordynamic performance of the oilfree TC is evaluated up to the rotor speed of 130 krpm, which is measured at the compressor end. The journal GFBs are modified to enhance the rotordynamic performance by inserting three metal shims between the bumpstrip layers and bearing housing. The rotordynamic performance is also measured during onroad tests by replacing the original TC of the test diesel vehicle with the constructed oilfree TC. The journal GFBs have a relatively large bearing clearance and no metal shims to generate subsynchronous motions at low TC and EG speeds. During normal vehicle driving, the TC rotor motions show steady rotordynamic operations. The oilfree TC rotates at 25 krpm ∼ 50 krpm while the vehicle runs at 20 km/h ∼ 30 km/h on the road. Subsynchronous rotor motions initiate with a frequency of ∼100 Hz at the TC speed of ∼37 krpm. As expected, the TC rotor motion also shows multiple EGinduced harmonics. Upon external shocks, produced by driving the vehicle on roadbumps, the subsynchronous motions are only excited when the rotor rotates above the initiation speed of subsynchronous motion. The excitation is nondestructive because the vehicle suspension absorbs most of the external shock. Incidentally, the external shocks appear to have no influence on the synchronous motion and engineinduced harmonics of the TC rotor.