motorverkningsgrad

Motorverkningsgrad, often translated as mechanical efficiency, is the ratio of useful mechanical power delivered by a motor to the energy supplied to the motor. It applies to electric motors as well as internal combustion engines and other prime movers. The value is dimensionless and usually expressed as a percentage.

For electric machines, η = P_out / P_in, where P_out is shaft power and P_in is electrical input power. Losses include copper losses in windings, iron (core) losses, and mechanical losses in bearings and seals. Efficiency depends on load and speed, typically peaking near rated load and decreasing at very light or very high loads.

For internal combustion engines, mechanical efficiency is the ratio of brake power to indicated power: η_mech = P_brake / P_indicated. Indicated power is the engine's internal power; brake power is the shaft output. Typical mechanical efficiency ranges from about 70% to 95%, depending on design, condition, and operating point, with losses from friction, timing gears, and accessory drives.

Efficiency is one component of overall energy efficiency. In vehicles, the overall efficiency combines thermal and mechanical components with driveline losses. Industrial practice uses brake dynamometer tests to measure efficiency, with corrections for temperature, altitude, and lubrication conditions.

Improving motorverkningsgrad reduces energy consumption and emissions. Strategies include reducing copper and iron losses, minimizing friction and windage, improving cooling and lubrication, and using high-efficiency motors or optimized engines and transmissions.

See also: efficiency, brake power, indicated power, energy efficiency.