Mk2 Balancing machine

TURBO TECHNICS LIMITED

All high speed machinery needs to be balanced to fine limits. In the case of the turbocharger, this has traditionally been achieved by careful balancing of individual components which normally ensures an adequate level of balance for heavy duty applications, typically large diesels.

The advent of the passenger car turbocharger has brought with it a more demanding requirement because of the higher rotational speeds and the more exacting demands of the installations. The typical car engine is light in construction and hence susceptible to vibration sources, and the vehicle driver will not tolerate even modest noise levels.

For these reasons, the car turbocharger requires balancing to much finer limits, and this cannot be achieved by balancing of individual components alone. Assembly tolerance stack-up means that even carefully balanced components, when assembled in a group, can give a cumulative imbalance which is unacceptable, while geometric errors in shaft straightness, squareness of faces etc. can also considerably influence the total assembly. The problem is exaggerated when parts are re-used in reconditioned units.

The solution to this problem is to achieve a more precise state of balance which can only be attained by balancing the complete assembly over a speed range close to the maximum operating speed of the unit.

Turbo Technics have developed the "vibration sorting" technique for service use and have been producing machines employing this principle since 1983. The method has been improved and refined over several years' experience of balancing Turbo Technics' own production units, and is the same as used by major manufacturers.

The increasing range of turbochargers in use today has created the need for a machine which has greater versatility and shorter cycle times. The original machine has been refined to achieve both of these aims at lower cost, using trim balancing of the compressor end to shorten the balancing process.

The complete centre housing / rotation assembly is held by quick release clamps in a turbine housing and driven by compressed air at speeds of up to 140,000 rev/ min. Full flow lubrication is provided to the bearings, and a shroud covers the compressor wheel. The nose nut is magnetised and the shaft speed is then monitored by a pick-up coil within the shroud support.

In operation, the speed of the unit is displayed, and an accelerometer attached to the turbine housing mount converts the acceleration signal to an electrical signal which is then analysed before display. A narrow band-pass tracking filter eliminates signals at frequencies other than those at the rotation frequencies, and the result is displayed as the vibration magnitude. In addition, the phase angle between the out of balance signal and a reference point is shown on a circular LED display to allow trim balancing.

In operation, the components of the rotating assembly would first be re-orientated to achieve an initial stage of balance. The unit would then be finally trim balanced by removing metal from the compressor nose nut.

Proper balancing of rotating assemblies will completely eliminate noisy turbochargers. Additional benefits accrue from longer bearing life, and a more professional and reliable turbocharger repair.