Direct drive mechanism

Direct drives are drives in which the electric motor and the driven equipment are directly connected. The engine is designed so that it directly has the speed of the work machine, a transmission is omitted.

Typical examples of direct drives are stationary grinders ( bench grinder ), fans and water pumps, which are usually operated with asynchronous motors.

Also in many conventional machine tools such operated on the AC line voltage induction motors are used at speeds of nearly 3000 or 1500 min -1 - the so-called standard motors. Any other speeds require a gearbox. The additional transmission losses, the overall efficiency decreases and there is an additional game, which is for example, positioning drives problematic. The design and the speed change are more complicated. Direct coupling of the tool spindle without gear (direct drive) can eliminate these problems.

Lower or high speeds can be achieved with standard motors with frequency converter ( FU) or by special motors with higher pin counts. One and the same induction motor can provide you with a FU over a wide speed range to be rated torque.

If the speed is high, not only the transmission can be saved, but also the mass of the engine is lower, as the power output increases at the same torque with increasing speed.

However, if a low speed is required, a suitable direct motor driving is often heavier than a gear motor ( gear reducer fast motor ).

Pros and Cons

  • Transmission and costs attributable
  • Less wear and noise
  • Lower in high-speed direct drive volume, low mass, high power density
  • Higher stiffness of the system, not a game
  • Compact design
  • High dynamics

For the purpose of direct-drive low-speed engines are heavier for the same power or they have only a small torque. Direct drives often require specially designed engines that not only produce special speeds, but often must also have robust storage to accommodate additional bearing forces or imbalances. Therefore, they can often only be used when produced in large quantities products.

Examples

Examples of direct drives are vacuum cleaner fan ( universal motor ), mixers, centrifuges ( laboratory centrifuges, fruit juice centrifuge ), fans, and clothes dryers. Often, the speeds are a subdivision feature:

Slow runner

A high number of poles, the speed is significantly reduced in existing supply frequency. While a standard motor usually 2 - or 4 -pole is at 50 Hz and therefore a speed of 3000 or 1500 min - 1 has, has a 30 -pole machine has a rated speed of 200 min -1.

Low speed with high number of poles have a large diameter, which can be several meters.

A classic application of slow-moving ones are, for example, the generators in hydroelectric power plants: for example, with the speed of 65.2 min -1 and a number of poles 92

The speed of synchronous generators or induction motors can vary if they are connected via a frequency converter.

Slow runners are often permanent-magnet DC motors or (partly electronically commutated ) multi-pole synchronous motors.

  • Direct -connected wind generators: typical data: 3 MW, 15 Hz frequency, speed about 17 min-1, Number 100, diameter 5 m
  • Cableway or conveyor drive: Integration of the engine in the pulley
  • Azipod propulsion ( ships): direct-drive propeller
  • ICE drive mounted directly without gear on the axle, FU - fed, speed 0-1750 min-1
  • Turntable direct drive ( higher quality turntable )
  • Bobbins or mandrels ( higher quality tape recorders )
  • Direct drives for vehicles Gearless hub motors for bicycles, cars and maimed vehicles
  • Gearless hub dynamos for bicycles
  • Dynastart, a starter - generator combination directly on the motor shaft of automobile internal combustion engines

Fast runner

High speed run much faster than standard motors. There are engines, reaching over 100,000 min - 1, for example when used in electric turbochargers. This is achieved by a power supply frequency with a frequency of several hundred Hz to about 1000 Hz, the engine is smaller compared to a standard motor with the same performance. The rotating parts must withstand some major radial accelerations (centrifugal force ).

  • Spindle drive for textile machines: integrated directly into the spindle, highly dynamic
  • Spindle motor for machine tools
  • Turbo -molecular pump ( a vacuum pump ), ca to 100,000 min-1
  • Electric Turbocharger speed 130,000 min-1

Direct drive for vehicles

The direct drive has been and is also used in the propulsion of vehicles. Electric motors or steam engines can drive the wheels of vehicles without gears. In internal combustion engines is when a drive of the wheels is to take place, a gear or a hydraulic or electrical power transmission required. A propeller can be operated by an internal combustion engine without a gearbox.

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