Efficiency
Ratio of output power to input power (η = P_out / P_in) — the measure of energy efficiency of a gearbox or drive system, expressed as a dimensionless value between 0 and 1 (or 0–100%).
Definition
Efficiency (η, eta) is a dimensionless parameter that describes what fraction of the supplied energy is actually delivered as usable output power. The difference from unity corresponds to the power losses, which are generated primarily as heat through friction. In gearboxes, tooth flank losses, bearing losses, churning losses, and seal losses all contribute to the overall efficiency.
Typical efficiencies: spur gearboxes 97–99% per stage, bevel gearboxes 95–98%, worm gearboxes 40–95% (depending on lead angle and lubrication), ball screws 90–98%. For multi-stage gearboxes, the stage efficiencies multiply: η_total = η₁ × η₂ × η₃. Efficiency directly influences the required motor power and heat generation.
Typical Efficiencies by Gearbox Type
| Gearbox Type | Efficiency η |
|---|---|
| Spur Gearbox (1 stage) | 97–99% |
| Planetary Gearbox | 95–98% |
| Bevel Gearbox | 95–98% |
| Worm Gearbox | 40–95% (dependent on i) |
Practical Relevance
Poor efficiency means high power loss, elevated operating temperature, and a larger motor requirement. For a worm gearbox with η = 0.6 and 10 kW of output power, 16.7 kW must be supplied — 6.7 kW heats the gearbox and requires cooling or oil change intervals. The TEA calculator helps match motor power and efficiency to each other.