How does gear efficiency generally change with increasing load?

• A. Efficiency increases only when lubrication is applied
• B. Efficiency remains constant regardless of load
• C. Efficiency increases with load indefinitely
• D. Efficiency typically decreases with higher load due to more friction and heat

Answer: (D)

When gear efficiency is considered, it’s about how much input power actually becomes useful output torque. As load on the gears increases, the internal friction from tooth contact and from bearings grows. Higher contact pressure means more sliding losses at the tooth interfaces, and bearing friction rises with the greater torque being transmitted. The lubricant must also shear and move more oil, wasting energy as heat. All these losses accumulate, so more input power is diverted to heat rather than to output work, causing efficiency to typically drop as load rises. Lubrication helps reduce these losses, but it doesn’t prevent the downward trend with increasing load.