Turbocharger Test Rigs
Electric Motor Driven
Designed by: Ankur Ashtekar
A 5000 rpm, 20 HP vector drive electric motor coupled to a belt pulley system and a gear box is used to drive the turbo charger test rig up to 70,000 rpm. The belt-pulley drive is used to increases the motor speed by 3.5 times. The output pulley drives a gearbox, which further increases the speed by another 4.21 times. The gearbox and the turbocharger assembly are coupled through a high speed flexible disc coupler. The assembly is aligned using a laser assisted system. The test rig along with its lubrication system is operated inside a reinforced room and monitored from a remote station through a set of wireless routers and cameras. In the following sections various attributes of the test rig are discussed.
Turbocharger Assembly: Figure 1 provides details of the bearing rotor assembly. The turbocharger rotor is supported by two back-to-back angular contact ball bearings. The two bearings used in the rig have a single one piece outer race which is supported inside the bearing housing by a pressurized squeeze film damper. An anti-rotation pin restricts the motion of the outer race about and along the axis of shaft rotation (i.e. X-axis). Two feed through holes in the outer race are used to supply oil to the bearing.
Rotor Design:The turbocharger has turbines which are used to rotate the rotor and drive the centrifugal compressors which supply pressurized air to the combustion chamber. This operation is entirely dependent on aerodynamic action of the fins on the turbine and the compressors. However, in this study, turbine and compressors were replaced with equivalent wheels which do not have fins and therefore do not generate any aerodynamic forces. This significantly reduces the complexity associated with the air circulation and discharge to operate the turbocharger test rig. A 20HP electric motor was used to drive the bearing rotor system at full speed under desired test conditions. The wheels were designed to have the same mass, CG location, and moment of inertia as the original rotor assembly.
Rotor and Component Balance:The equivalent rotor assembly was dynamically balanced to ISO G2.5 standard. Each rotor part was independently balanced before assembly and later the complete rotor assembly was also balanced to the same specifications. Nevertheless, the rotor was designed to allow for adding external weights around the periphery to create controlled imbalance. Each plane has 12 equally spaced threaded holes, as shown in Figure 2, which can be plugged to add small amounts of controlled imbalance to the rotor and observe its effect on the rotor and bearing dynamics.
Lubrication System: A recirculating lubrication system was used to supply pressurized oil (50 psi) to the turbocharger test rig. The lubricating oil is pumped through a heat exchanger to maintain the desired lubricant temperature before it is supplied to the turbocharger bearings, squeeze film damper and the gear box. The cooled oil is then filtered to remove contaminants particles of 10 Ã‚Âµm and larger. Approximately 1 gallon per minute of oil is supplied to the turbocharger bearing housing where it forms a pressurized squeezed film damper to support the bearing outer race inside the housing. Feed through holes on the bearing outer race directs part of this oil to the bearings. The lubricating oil is then drained back to the sump. The gear box used in the TTR requires oil mist lubrication and therefore the oil is mixed with air and supplied to the gearbox at 20 psi. The oil mist exhaust from the gear box is passed through an oil trap to separate oil from air. The separated oil is then drained back to the sump.
Displacement Proximity Sensors:Rotor displacements were measured using non-contact inductive proximity sensors. Four sensors were used to measure the circumferential (YZ) and out of plane (XY and XZ) displacements of the rotors. Figure 3 depicts the placement of the proximity sensors around the rotor to measure circumferential displacements. National Instruments data acquisition hardware and custom LabVIEW software program were used to collect and analyze the displacement data.