As the market penetration of electric heavy-duty trucks continues to grow, many users still have a limited understanding of their key configurations-particularly the electric drive axle. As the core component of the EV axle system, the electric axle directly affects vehicle performance, efficiency, and operating cost.
What are the main types of electric truck axles, and what factors should be considered when selecting an EV axle or e-axle system? This guide provides a detailed analysis from multiple dimensions, including axle structure, number of motors, transmission gear design, and power take-off (PTO) configuration.
01 Structure of the Electric Drive Axle
A traditional truck drive axle consists of four main assemblies, most of which are still retained in modern electric axle systems.
1. Axle Housing
The axle housing is the primary load-bearing component of both conventional and electric truck axles. Common manufacturing processes include stamped steel welding, hydraulic expansion, and precision casting. These mature technologies are widely used in EV axle platforms to balance cost, weight, and strength.
2. Main Reducer
The main reducer converts input torque into wheel-end output torque. In both diesel and electric drive axle applications, parameters such as back tooth diameter (e.g., 485, 440, 400) indicate torque capacity and load-bearing strength. Larger diameters generally correspond to higher wheel-end torque, which is critical for electric heavy-duty trucks.
3. Wheel End
The wheel end supports high-speed rotation and heavy loads. Modern electric truck axles typically use maintenance-free wheel ends, reducing service frequency and lifecycle cost-an important advantage for EV fleets.
4. Braking System
Drum brakes and disc brakes are both used in electric axle applications. Wedge brakes have become mainstream in heavy-duty electric axle systems due to their compact structure and responsive braking performance.
Example: In most EV axle designs, the axle housing, wheel end, and braking system remain largely consistent with traditional truck drive axle architecture.
Electric Drive Axle Structural Types
Electric drive axles used in heavy-duty EVs generally adopt one of two structural layouts.
Structure 1: Integral Axle Housing (Integrated EV Axle)
This design retains the traditional axle housing, wheel ends, and braking system, while integrating the motor + transmission assembly at the front flange. Torque from the electric motor is transmitted through the gearbox to drive the wheels.
Example: An electric heavy-duty truck equipped with an integral axle housing electric drive axle.
This type of EV axle system offers low cost and high maturity, as it reuses conventional truck drive axle components. However, space limitations typically restrict the transmission to two or three gears, and PTO integration is often not possible.
Example: An electric heavy-duty truck equipped with a three-section electric drive axle.
Structure 2: Three-Section Axle Housing (Modular E-Axle System)
In this configuration, the left and right axle housings are separated, with the electric motor, transmission, and optional PTO integrated into the center section. This modular e-axle system allows for multi-speed transmissions (3–6 gears), improving both power performance and energy efficiency.
Although the three-section design increases weight slightly due to flange connections, its load-bearing capacity is reliable and suitable for heavy-duty EV applications.
Example: Electric heavy-duty trucks are equipped with a three-stage electric drive axle.
Industry Trend Insight:
While integrated EV axles dominate the current market due to cost advantages, modular electric axle systems with multi-speed transmissions represent the future development direction.
02 Selection of the Number of Motors
The latest self-developed heavy-duty truck electric drive axle uses a single motor.
Most electric drive axles for heavy-duty trucks use a single motor due to installation constraints. Typical single-motor EV axle specifications include peak power outputs of around 390 kW and peak torque exceeding 700 Nm.
To achieve higher performance, dual-motor EV axle systems are increasingly adopted. These systems may use:
Front–rear motor arrangements driving a common reducer, or
Distributed motor designs eliminating the traditional main reducer.
A representative example is the Tesla Semi, which uses a dual-motor electric axle system with electronic differential control.
Example: Electric drive axle of the Tesla Semi electric heavy-duty truck.
Operational Strategy Advantage:
Dual-motor EV axles allow intelligent power distribution. Both motors operate during heavy-load starts and climbs, while single-motor operation is used during cruising to maximize efficiency.
03 Transmission Gears in Electric Axle Systems
Compared to diesel engines, electric motors have a broader operating efficiency range. As a result, electric truck axles do not require as many gears as traditional transmissions.
Integrated EV axles typically use 2-speed gearboxes
Modular e-axle systems can support 3-, 4-, or 6-speed transmissions
For example, a modern electric drive axle with a 3-speed gearbox can achieve wheel-end torque of up to 48,700 Nm, sufficient for demanding heavy-duty applications.
Gear Selection Recommendation:
Flat regions: 2-speed EV axle
Hilly terrain: 3-speed e-axle system
Mountainous regions: 4-speed electric axle system
04 Power Take-Off (PTO) Design in EV Axles
Example:This electric heavy-duty truck's electric drive axle does not include a PTO
Early electric axle designs often lacked PTO functionality due to space limitations. In such cases, an auxiliary motor was required to drive hydraulic systems, adding unnecessary weight and cost.
Example:Newly developed electric drive axle with the motor on the left, transmission in the center, and PTO on the right.
Modern EV axle kits increasingly integrate PTO capability directly into the electric drive axle. This is particularly important for dump trucks and resource-transport vehicles that rely on hydraulic systems.
Recommendation:
Even if a PTO is not immediately required, selecting an electric axle system with PTO improves long-term flexibility and resale value.
Large battery capacity, long driving range, and advanced electric drive axles define the future of electric heavy-duty trucks. Selecting the right EV axle, e-axle system, or electric truck axle configuration requires careful consideration of operating conditions, terrain, and application requirements.
