Based on the number of gear reduction sets, final drive reducers can be classified into single-stage and dual-stage. Except for medium and heavy-duty vehicles requiring a large reduction ratio, most micro, light, and medium-duty vehicles use single-stage final drive reducers.
•Dual-stage Reducer
When the final drive reduction ratio is large, a dual-stage final drive reducer is required to ensure the vehicle has sufficient ground clearance. A dual-stage reducer includes an additional intermediate gear. The left side of the driving bevel gear meshes with the bevel part of the intermediate gear. Coaxially with the bevel gear, there is a small-diameter spur gear, which meshes with the driven gear. This causes the intermediate gear to rotate backward and the driven gear to rotate forward. There are two stages of reduction in between. Dual-stage reducers increase the axle volume and were previously mainly used in vehicles with lower engine power. Currently, they are primarily used in low-speed, high-torque construction machinery.
In a dual-stage final drive reducer, if the second stage of reduction occurs near the wheels, effectively forming independent components at the two wheels, it is called a wheel-side reducer (or hub reduction unit). The advantage of this is that it reduces the torque transmitted by the half-shaft, which helps to reduce the size and mass of the half-shaft. Wheel-side reducers can be planetary gear type or consist of a pair of cylindrical gear sets. When using cylindrical gear sets for wheel-side reduction, the vertical relationship between the wheel axle and the half-shaft can be changed by adjusting the relative positions of the two gears. This type of axle is called a portal axle and is often used in vehicles with special requirements for axle height.
•Single-stage Reducer
A single-stage reducer consists of a driving bevel gear (commonly known as a pinion) and a driven bevel gear (commonly known as a ring gear). The driving bevel gear connects to the driveshaft and rotates clockwise. The driven bevel gear is positioned to its right, with the mesh point rotating downwards, consistent with the forward direction of the wheels. The reduction function is achieved because the driving bevel gear has a smaller diameter and the driven bevel gear has a larger diameter.
•By Number of Reduction Ratios
Based on the number of reduction ratios, final drive reducers can be divided into single-speed and dual-speed types. Currently, most domestic automobiles use single-speed final drive reducers with a fixed reduction ratio. Dual-speed final drive reducers offer two selectable reduction ratios, effectively functioning as an auxiliary transmission.
•By Structural Type
Based on the structural type of the reduction gear set, they can be classified into cylindrical gear type, bevel gear type, hypoid gear type, and others.
In drive axles of vehicles with transversely mounted engines, the final drive reducer often uses simple helical cylindrical gears. In drive axles of vehicles with longitudinally mounted engines, the final drive reducer often uses bevel gears and hypoid gears. Compared to bevel gears, hypoid gears offer smoother operation, higher bending strength and contact strength, and also allow the axis of the driving gear to be offset relative to the axis of the driven gear.
Automotive final drive reducers widely use spiral bevel gears and hypoid gears. When hypoid gears operate, the pressure and sliding between tooth surfaces are significant, making the tooth surface oil film susceptible to breakdown. Therefore, hypoid gear oil must be used for lubrication; ordinary gear oil must never be substituted, as this would quickly lead to scuffing and wear of the tooth surfaces, significantly reducing service life.
