Working conditions of gear oil in gear reducers and its functions

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Gears in various mechanical transmission mechanisms can be classified into parallel shaft transmission, intersecting shaft transmission, and skew shaft transmission, depending on the relative positions of their axes. Within each type of transmission, there are different transmission methods depending on the shape of the gears and teeth; for example, in parallel-axis transmissions, there are straight-cylinder gears, helical-cylinder gears, and herringbone-cylinder gears ； Intersecting-axis drives include straight-bevel gears, helical bevel gears, and spiral bevel gears ； Interaxial drives include hyperbolic gears, worm gears and worms, as well as screw drives. 1. Characteristics of gear drives and working conditions of gear oil (l) Gear drives have high efficiency; the efficiency of conventional cylindrical gear drives can reach 98%. Compared to bearings, gears have a smaller equivalent curve radius, resulting in poorer oil wedge conditions. (2) In gear transmission, there is linear contact between the teeth, so the contact area is small and the contact pressure per unit area is high. The unit contact pressure of ordinary automotive gears can reach 2000–3000 MPa, while that of hyperbolic gears is even higher, reaching 3000–4000 MPa. (3) Gear drives involve not only linear contact but also sliding contact; especially in hyperbolic gears, there is a high relative sliding speed between the gear teeth, which can generally reach around 8 m/s. Under high-speed and high-load conditions, this can cause the oil film to thin out or even break locally, leading to increased friction and wear, as well as scratches and galling. (4) The operating temperature of gear oil is generally lower than that of internal combustion engine oil, and it varies to a large extent with the ambient temperature; the temperature of vehicle gear oil usually does not exceed 100°C. Modern cars use hyperbolic gears; due to the large offset of their axes, high vehicle speeds result in a very high relative sliding speed between the gear surfaces, causing the oil temperature to reach 160°C to 180°C. 2. The role of gear oil in gear drives: (1) Reducing wear on gears and other moving parts, thereby extending their lifespan. (2) Reduce friction and minimize power loss. (3) Disperse heat and exert a certain cooling effect. (4) Prevent corrosion and rusting. (5) Reduce working noise, minimize vibration, and lessen the impact between gears. (6) Flush away dirt, especially the debris between tooth surfaces, to reduce wear.