Posted tagged ‘rotor’

Super Charger

September 28, 2011


Engines combust (burn) fuel and use the energy of that combustion to do work. The more fuel that is combusted in any given time then the more energy is available to carry out the engines task. Fuel requires air (or the oxygen contained within air) to burn so if there isn’t enough air mixed with the fuel it will not burn. This also means that the amount of air entering an engine determines how much fuel can be burnt and consequently how much energy (or power) an engine can produce. Superchargers are essentially an air pump designed to cram extra air into an engine allowing it to combust more fuel than would otherwise be possible.


Mercedes pioneered automotive superchargers on their race cars during the 1920’s. These were simple reciprocating compressors attached to the engine by an electrically operated clutch. A switch activated by the accelerator pedal turned the pump on when extra power (full throttle) was required. A flurry of engineering endeavor ensued in order to reign in Mercedes advantage on the racetrack. Within a few short years most of the basic designs for modern superchargers had appeared.


During the 1930’s superchargers were largely the preserve of marine engines, aircraft and race vehicles but gradually found their way into commercial diesel engines by the 1950’s. It has been common for truck engines to be turbo supercharged (a.k.a. turbocharged) for decades but car engines originally had difficulty in effectively employing this technology.


Superchargers mostly fall into one of two categories, mechanically driven superchargers and turbo superchargers driven by exhaust gasses. A third category is starting to make an appearance and that is electrically powered superchargers.


Turbo superchargers (a.k.a. turbochargers or turbo’s) are relatively compact, lightweight and efficient but suffer from turbo lag and heat stress. By turbo lag we mean the amount of time it takes for the turbo’s rotor to speed up to full efficiency. Some of the earliest turbo charged vehicles took so long for the turbo to produce a usable amount of boost that they were all but useless. Modern turbo chargers are much better in this regard but turbo lag is still a problem. Heat is another bane of turbo chargers. Exhaust gasses are extremely hot and can cause so much heat to build up in the turbo that oil will burn and congeal within its galleries leading to a bearing failure. This is why many turbo chargers have a turbo timer. The timer will cause an engine to continue idling for a few minutes after it is switched off allowing excess heat to be dissipated.

01-super charger schematic diagram

Mechanically driven superchargers usually don’t suffer from turbo lag and can often produce more boost than an exhaust driven charger (turbo). On the negative side they are generally bulky, heavy, and have a cumbersome drive mechanism (usually belt drive). Furthermore most chargers of this type have to supply air at all engine speeds and loads making them difficult to match various engine conditions precisely.

As our supercharger is electrically driven we have devoted an entire article to the advantages and disadvantages of this type.

Heat exchangers (intercoolers) are frequently used in conjunction with superchargers. Compressing air increases its temperature thus making it less dense. By re-cooling the compressed volume of air before it enters, density is increased allowing even more air to be forced into the engine. Intercoolers are more important for turbo superchargers as there are two heating sources present, the act of compression and heat from exhaust gasses both increase air temperature.


August 22, 2011

01-Magnetic_Bearing-magnetic bearing technology-active non contact position sensors

Magnetic bearings have been utilized by a variety of industries for over a decade with benefits that include non-contact rotor support, no lubrication and no friction.

Conventional mechanical bearings, the kind that physically interface with the shaft and require some form of lubrication, can be replaced by a technology that suspends a rotor in a magnetic field, which eliminates friction losses.

01-floating rotors-magnetic bearing technologies-SKF compressor drive-advanced drive system

There are two types of magnetic bearing technologies in use today – passive and active.  Passive bearings are similar to mechanical bearings in that no active control is necessary for operation. In active systems, non-contact position sensors continually monitor shaft position and feed this information to a control system.  This in turn, based on the response commanded by the system, flows to the actuator via current amplifiers.  These currents are converted to magnetic forces by the actuator and act on the rotor to adjust position and provide damping.

Additional benefits of magnetic bearings include:

  • No friction
  • No lubrication
  • No oil contamination
  • Low energy consumption
  • Capacity to operate within a wide temperature range
  • No need for pumps, seals, filters, piping, coolers or tanks
  • Environmentally friendly workplace
  • Impressive cost savings

In practice, these attractions are balanced in order to maintain a gap between the shaft (rotor) and static parts (stator). The function of the magnetic bearing is to locate the shaft’s rotation axis in the center, reacting to any load variation (external disturbance forces),

01-typical examples for Floating rotors to run a heavy machineries-magnetic bearing systems to run shaft without friction

Floating rotors could boost compressor efficiencies

Traditional centrifugal compressors are based on low-speed drives, mechanical gears and oil-film bearings, resulting in high running costs because of their high losses, wear, and need for maintenance.

This new compressor drive (above) uses a permanent magnet motor, operating at an efficiency of around 97%, to drive a rotor “floating” on magnetic bearings, which spins the compressor impeller at speeds of around 60,000 rpm. These drives experience almost no friction or wear, and need little maintenance. They also minimize the risk of oil contamination, and result in compressors that are about half the size of traditional designs.

How they work


01-general-magnetic-principles-monitoring the air gap of shaft and bearings contact and position-position sensor-closed loop system-controlling of shafts in center position-position controller
Magnetic bearings are basically a system of bearings which provide non-contact operation, virtually eliminating friction from rotating mechanical systems. Magnetic bearing systems have several components. The mechanical components consist of the electromagnets, position sensors and the rotor. The electronics consist of a set of power amplifiers that supply current to electromagnets. A controller works with the position sensors which provide feedback to control the position of the rotor within the gap.

01-magnetic-5 axis shaft control-radial bearings-air gap- advanced bearing technologies

The position sensor registers a change in position of the shaft (rotor). This change in position is communicated back to the processor where the signal is processed and the controller decides what the necessary response should be, then initiates a response to the amplifier. This response should then increase the magnetic force in the corresponding electromagnet in order to bring the shaft back to center. In a typical system, the radial clearance can range from 0.5 to 1 mm.

This process repeats itself over and over again. For most applications, the sample rate is 10,000 times per second, or 10 kHz. The sample rate is high because the loop is inherently unstable. As the rotor gets closer to the magnet, the force increases. The system needs to continuously adjust the magnetic strength coming from the electromagnets in order to hold the rotor in the desired position.