Advantages and Disadvantages of Parallel-Axis Electric Axle VS Coaxial Electric Axle

The traditional drive axle is located at the end of the transmission system, and its main function is to decelerate and increase the torque of the power coming from the transmission, and transfer the power to the drive wheels. However, with the continuous progress of motor technology, the performance of drive motors has been significantly improved, and the role of ordinary rear axle in decelerating and increasing torque has been gradually weakened. Therefore, electric drive axle technology has emerged and is becoming an important trend in the future development of electric vehicles.

The central integrated electric drive axle has become the mainstream in the current market due to its high integration, high transmission efficiency, mature technology, easy maintenance and other advantages. The integrated electric drive axle is mainly divided into three types: parallel-axis type, same-axis type and vertical-axis type according to the arrangement of motor and drive axle.

Vertical-axis electric drive axle due to structural problems, compared with the same-axis and parallel-axis electric drive axle performance is inferior. Parallel-axis electric drive axles and coaxial electric drive axles have their own advantages.

Parallel-Axis Electric Drive Axle

Structural characteristics: The motor and the output half-shaft of the drive axle are arranged in parallel, and the motor is usually placed on one side.

Advantages

• High technological maturity: Based on the evolution of the traditional drive axle structure, the technology is relatively mature.
• Low cost: low up-front investment, low development difficulty, high cost performance.
• Convenient arrangement: the rigid axle housing, half shafts and other resources of the traditional drive axle can be borrowed to the maximum extent.

Disadvantages

• Bias load problem: due to motor bias, it is easy to lead to uneven load distribution on the power transmission path.
• Larger space occupation: Compared with the coaxial type, the parallel-axis type electric drive axle has a relatively complex structure and occupies slightly more space.

Coaxial Electric Drive Axle

Structural characteristics: The motor and the output half-shaft of the drive axle are arranged coaxially.

Advantages

• High degree of integration: compact structure, reducing space requirements.
• High transmission efficiency: short transmission path, low energy loss.
• Better NVH performance: the coaxial electric drive axle has better NVH performance than the parallel-axis type.
• Lightweight: light unsprung mass, which helps to improve the handling of the whole vehicle.

Disadvantages

• Difficult to develop: High-speed hollow motor and planetary row gears need to be developed, which is technically difficult.
• Higher cost: Highly integrated design increases manufacturing cost.
• High motor requirements: single-stage or two-stage gearboxes are usually used, requiring high motor performance.

Comparison

	Coaxial electric drive axle	Parallel-Axis Electric Drive Axle
Compactness	Highly integrated, compact structure, small size, easy to arrange for the whole vehicle.	Relatively decentralised structure, but compact arrangement can be achieved through optimised design.
Transmission efficiency	Short transmission path, high efficiency, reduced energy loss.	Higher efficiency, but may be slightly lower than coaxial electric drive axle.
NVH performance	Better NVH performance due to compactness.	NVH performance is also good, but relatively difficult to optimise.
Cost	Higher development and manufacturing costs, but cost-effective in the long run.	Lower cost, mature technology, simple processing and manufacturing.
Weight	Lighter weight with lightweight design.	Relatively light weight, but may not be as light as coaxial electric drive bridges.
Maintenance	Relatively complex to maintain, but highly reliable.	Easy to maintain, as the motor and reducer can be dismantled separately.

Summary

Coaxial electric drive axle and parallel-axis electric drive axle each has its advantages and disadvantages, in practical applications of the two electric drive axle programme are more desirable, the final choice of which type of electric drive axle needs to be based on the specific needs, application scenarios, and cost and other factors for comprehensive consideration. So you think the centralised electric drive axle design, the future will be towards that trend and direction?

For more information about electric axle systems for commercial vehicle please click Brogen Electric Axle.

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