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Various electric motors, with 9 V battery as a size comparison
A Mercedes V6 racing engine from the DTM

A motor [ engine ] (also [ engine ]; latin motor , mover ') is a combustion engine , the mechanical work done by a form of energy such. B. thermal , chemical , hydraulic , pneumatic or electrical energy , converted into kinetic energy.

As a rule, motors have a shaft that sets them in rotation and drives mechanical devices such as gears through them . Exceptions are rocket motors and linear motors . Today, combustion engines and electric motors are of paramount importance.

History of the engine

The earliest engines may have been Heron's smoke turbines for opening large gates around the year 100 . Assumptions about the handling of the Egyptian priesthood with hot gases to move huge doors are also plausible.

Around 1670 Ferdinand Verbiest is said to have built the working model of a steam car in the service of the Emperor of China . As with earlier smoke turbines, the operating principle was based on the Heronsball . The vehicle is described in Verbiest's writings, which were summarized in 1681 as Astronomia Europea in Latin, where he first used the term engine in today's sense. However, there are no authentic images of this vehicle.

The technical development of today's engines began understandably with the steam engine invented by Thomas Savery and Thomas Newcomen and further developed by James Watt in 1778 .

The steam engine changed the economic and social structures of Europe and triggered the industrial revolution . There were not only stationary machines, but after Richard Trevithick's invention of the high-pressure steam engine, there were also locomotives (a mobile, partly self-propelled steam engine for driving threshing machines or for steam plowing ), steam locomotives , steam ships , steam tractors and road rollers .

In 1816 Robert Stirling invented the hot gas engine that was later named after him . He was looking for a machine without the potentially explosive boiler.

One of the first usable internal combustion engines - a gas engine based on the two-stroke principle - was invented by Étienne Lenoir , improved in 1862 by Nikolaus August Otto through the development of the four-stroke principle and later named after him. The gasoline engine was initially too big and too heavy in an automobile to be installed to. Gottlieb Daimler and Carl Friedrich Benz solved this problem almost simultaneously .

Even after the invention of the internal combustion engine, the steam engine was still a widely used drive - cheap coal or wood could be used as fuel. Due to their better efficiency and the high energy density of the fuels, internal combustion engines have since come to the fore, which convert the chemical energy of the fuels inside into thermal energy and then into mechanical energy.

In the future, the aim is to change the energy source of mobile engines in order to counter the scarcity and thus the increase in the price of fossil fuels . This often also reduces the emission values . A prerequisite for this are practicable storage options for non-fossil fuels, especially for mobile use (accumulators, alternative fuels). Electric motors and hybrid drives are possible alternatives to replacing or supplementing the piston engine.

In all sizes, from toys to industrial plants , electric motors for direct current , alternating current and three-phase current are used ( electrical machines ). Many electric motors - especially those with permanent magnets - can also work as generators if they are mechanically driven.

Requirements for engines

Motors and other prime movers convert chemical, electrical, or thermal energy into mechanical energy ( work ). You should from a modern point of view

  1. have a high degree of efficiency - d. H. use the fuel optimally and therefore with low consumption ,
  2. cause few emissions or at least emit few pollutants ,
  3. develop the highest possible performance with a low weight,
  4. high operating reliability and service life have
  5. and have other special properties depending on the application.

At the beginning of engine construction - practically every one of the basic principles - was to achieve the necessary performance . In addition to the power (consumption of electricity or fuel and mechanical power output), other parameters of engines are also the mass , the speed and the efficiency .

Overview of different types

Types of engines

Steam engine

The steam engine is the "original engine" of industrialization over the past centuries. It was invented by Thomas Newcomen . It works with hot steam under pressure. Its pressure is absorbed by the steam piston . As with the internal combustion engine, a linear movement is converted into a rotational movement via a crank drive. There were already several types of this piston machine around 1850 .


Using a fire kettle in which the water is heated to boiling temperature or higher with a coal fire, the heated water creates expanding steam. This steam is fed from the crank mechanism of the steam engine via a mechanical control unit. The control unit ensures that the steam cylinder (in which the piston runs) of the crank mechanism only receives steam again when the expanded steam from the previous stroke cycle has largely escaped.

Motion implementation

The linear movement of the piston in the expanding cylinder space, into which the steam was previously let in, is converted into a rotary movement by a connecting rod on the crank pin or crank pin. This process is repeated continuously. What the means of transport releases from the chimney or exhaust is the steam emitted by the piston cylinder, mixed with the smoke from the furnace.

Steam turbine

It is the modern version of the heat engine and uses steam power with greater efficiency. Steam pressure drives a turbine , the rotation of which basically runs more smoothly than the back and forth of a steam piston. The torque curve is therefore flatter, that is, it works more evenly.

Internal combustion engines

Components of a typical four-stroke engine with an overhead camshaft: C:  Crankshaft E:  Exhaust valve camshaft I:  Air supply valve camshaft P:  Piston R:  Connecting rod S:  Spark plug V:  Valves W:  Cooling water ducts Red: Exhaust port Blue: Intake port

Combustion engines convertthe heat released during combustion into mechanical work by means of volume change workin thermodynamic cycles. The pressure of the combustion gases acts on the surface of a moving component (piston), whichconverts the volume change work of the gas forces into mechanical workvia acrankdrive ( connecting rod + crankshaft).

The efficiency of internal combustion engines is strongly dependent on the operating point due to the conversion of the chemically bound energy of the fuel via heat release into mechanical work . In the optimal operating condition, the effective efficiency of ship engines using the exhaust gas heat can be up to 55% ( Emma Mærsk class ). If one also takes into account the use of the cooling water heat ( block- type thermal power station ) and even the CO 2 emissions, such as B. for greenhouses, the benefit in relation to the effort can be over 90%. The efficiency of car engines when cold or even when idling can be less than 10%. A general statement is not possible and is closely related to the application (efficiency = benefit / effort or fuel consumption).

Optimization of internal combustion engines

To control the fresh air, the standard motors are controlled by valves or rotary valves that control the gases entering and leaving the work cycle synchronously .

A turbocharger or other air compressor can be used to supply fresh air with increased density, thereby increasing the efficiency of the engines. In petrol engines, the fuel supply is improved by injection nozzles . They are electrically controlled and can therefore be integrated into the modern electronic control of the motors. Similarly, the pump-nozzle system or common rail injection is used in diesel engines to improve performance.

Fuel cut-off and a start-stop system can be used to optimize fuel consumption.

Compression ignition (diesel engine)

If a fuel can be burned without aids - only through the high compression of the air-fuel mixture - then it is a self-igniter. It ignites by filling the combustion chamber with pressure . There have been improvements in the modification of the combustion chambers, pistons, injection nozzles and feed pumps as well as in the increase of the injection pressures, the associated better mixing of the fuel with the air and the systematic variation of the fuel metering. In the course of these developments, the eddy current chamber has been replaced by the direct injection.

The glow plugs of the diesel engine or multi-fuel engine are only aids for cold starting ; alternatively, highly flammable starting fuels can be fed in at start-up. There were no major innovations here, only modifications to the glow plugs.

Spark ignition (gasoline engine)

If the compression of the engine is not as high as in the case of the diesel, then it needs z. B. Spark plugs to ignite the reaction mixture.

Development and future

This engine group is the most frequently used in vehicle construction, especially as gasoline and diesel engines . She makes most of the vehicle actuators for cars and trucks , diesel , tanks etc., small aircraft and motor gliders, flight - and motor boats , yachts , lawn mowers and many other applications.

The combustion engine is mechanically a further development of the steam engine and, from today's perspective, has the best prerequisites for further optimization in consumption, efficiency and the use of materials for the engine. The optimization takes place partly through other fuels or working materials such as hydrogen , which produce almost pure water vapor, as well as through combinatorial uses of energy in hybrid drive concepts .

Gas turbines

Turbines with combustion gases belong to the “ thermal fluid energy machines” like the steam turbine , but belong to the group of internal combustion engines . They are both considered to be flow machines.

Each gas turbine has a turbo compressor , a combustion chamber and a turbine, which is usually mechanically coupled to the compressor via the same shaft. The air compressed by the compressor is burned in the combustion chamber at temperatures of up to 1500 ° C with the injected fuel. The combustion gases escaping at high speed drive the turbine (it is not required for rockets ). The turbine draws at least the flow energy from them that is necessary to drive the compressor. The rest is available as usable energy - either mechanical energy to drive a shaft (power station, helicopter) or as recoil.

Efficiency and Applications

The hotter the gases, the higher the efficiency of gas turbines. This, and the ideal shape of the turbine blades, offers great potential for development in engine construction. The thermal loading capacity of the blades and casing is essential here .

Applications in aviation are given by the very good power-to-mass ratio of the gas turbines, for example as an engine for helicopters or turboprop aircraft. The kinetic energy of the fuel gases can also be used for recoil propulsion in aircraft. In jets , so-called jet engines used, the principle of which substantially corresponds to the gas turbine: The three components of the pure gas turbine is followed by a nozzle , through which the exhaust jet emerges. The turbine only receives as much energy (rotational speed) as it needs to drive the compressor .

Applications in shipping : Here, a favorable power-mass ratio is less important than low fuel consumption . This is why the more efficient diesel engine, which, in contrast to the gas turbine, can also be operated with cheap heavy fuel oil, has replaced it in the civil sector. For military use it is occasionally used because of its smoothness. The gas turbine is also often chosen for hovercraft .

Use in power plants (a distinction is made between two types of gas turbines):

With some turbines, the angle of attack of the turbine blades can be changed; see also variable turbine geometry loader .

Stirling engine

The Stirling engine converts thermal energy into mechanical energy without the need for combustion. A temperature difference must be present and maintained on the motor for operation.

Rocket motors

Rocket motors usually generate mechanical energy from chemical energy via the detour of thermal energy. See also rocket , rocket technology .
Exceptions that work purely physically are:

Electric motor

The most commonly used motors are electric motors . Drives of the most varied of sizes and outputs can be found in practically all machines, devices, automats and production equipment - from miniaturized servo and stepper motors to devices for households, offices , air conditioning and cars to industrial plants.

The further development takes place less in the engine construction itself than in the optimization of its application, e.g. B. by power electronic control instead.

Electric motors are energy converters that convert electrical current into rotary or linear motion ( linear motor ). Larger asynchronous motors are often standardized ( DIN , Germany), which standardizes the production and use of motors. European electric motor products are often subject to the CEE standard.

Electric motors are available for direct current , alternating current and three-phase current . They are mainly used in industrial plants and for electrical machines . Also in toys or z. They are used, for example, in PCs (fans, drives, hard drives) and in household appliances .

Development trends are miniaturization and the combination with control technology (sensors, power electronics).

More recent developments relate to the large-scale application of superconductors , which is being worked on intensively. In addition to increased performance in motor construction, it will also affect transformer construction .

Almost all electric motors can also work “the other way around” as generators . H. generate electrical energy with mechanical drive. This z. B. when braking or in elevators energy can be recovered.

A special form of electric drives are the piezo motors .

Commission Regulation (EC) No. 640/2009

Inefficient motors (IE1 and below) may no longer be sold since June 16, 2011. From 2015, average IE2 motors with a rated output power of 7.5 to 375 kW will only be permitted with speed control . Alternatively, efficient IE3 motors can be sold with or without speed control.

Hydraulic motor

Hydraulic motors often work on the reverse principle of a gear pump . They generate a rotary movement from the pressure and flow of a hydraulic fluid. They are comparatively small and can generate high torques even at standstill. You will u. a. used on excavators, tunnel boring machines and in agriculture.

A derived variant can be found in fluid drives, but is not called that there.

Pneumatic drives

Compressed air is used to operate turbines (e.g. dental turbines (drills), centrifuges) or piston machines.


Hydropower and wind power play a role in the history of the engine. A water wheel is also a motor , an energy converter: The energy supply from water with a higher level ( potential energy ) of a pond or a river was converted into a rotary movement by means of a water wheel in order to drive millstones ( water mill ) or a sawmill .

A wind turbine is also a motor: the force of the air flowing past is used to e.g. B. to drive a millstone ( windmill ), a water pump or a generator.

Other historical drives worked with the muscle power of animals or humans (see Göpel ). Even today people or animals drive pumping stations in arid countries to convey water.

Web links

Wiktionary: Motor  - explanations of meanings, word origins, synonyms, translations
Commons : engine  - collection of images, videos and audio files

Individual evidence

  1. On the history of the motor vehicle . In: Automobiltechnische Zeitschrift . 2/1949, p. 40.
  2. Asynchronous motor with frequency converter www.kimo.de, accessed on January 21, 2015
  3. EU Ecodesign Directive (EuP Directive) ( Memento of the original from January 20, 2015 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF; 426 kB) www.bdew.de, accessed on January 20, 2015 @1@ 2Template: Webachiv / IABot / www.bdew.de