Different Types of Wheel-Side Drive: Introduction & Comparison

Most battery electric buses today utilize centralized drive systems. Two primary configurations dominate the market:

A. Direct-Drive Motor Systems

• The motor replaces the traditional engine position, offering a simple and mature design.
• Widely adopted due to its straightforward integration and reliability, making it the mainstream choice for battery electric buses.

B. Motor + AMT Transmission Systems

• Provides enhanced climbing performance, ideal for mountainous or scenic routes.
• Drawbacks include reduced reliability due to added automated shifting mechanisms and potential operational issues.

As electric drive systems evolve toward higher speeds, greater integration, and lightweight designs, distributed electric drive technology — exemplified by wheel-side drive systems — has begun to enter the practical stage.

Compared with centralized drive systems, wheel-side drive configurations eliminate the need for transmission shafts, main reduction gears, and differentials. This results in a shorter power transmission chain, higher transmission efficiency, and a more compact structure. In addition, precise control of wheel-side motor speed and torque enables integrated functions such as vehicle propulsion, braking, differential action, and energy recovery.

Owing to its high degree of control freedom and functional expandability, the wheel-side drive system has become a focal point in the research and development of battery electric bus powertrain systems.

Wheel-Side Drive Configurations

Wheel-side drive systems bridge the gap between centralized and hub motor designs. They typically integrate a motor with a fixed-ratio reducer mounted on the chassis, directly driving the wheel via short axles. Two primary configurations exist:

A. Fixed Wheel-Side Motor Configuration

The motor and reducer are rigidly mounted on the chassis, replacing traditional axle housings and half-shafts.

Advantages:

• Reduced weight and structural complexity.
• Compatibility with leaf spring or air suspension systems.
• High-speed motors paired with planetary gear reducers enable compact designs and dual-tire configurations for heavy-duty urban buses.

B. Swinging Wheel-Side Motor Configuration

The motor and reducer are integrated with independent air suspension, eliminating rigid axle structures.

Advantages:

• Reduced unsprung mass, improving ride comfort and handling.
• Increased cabin space and lower floor height.
• Ideal for low-floor city buses, enhancing accessibility for passengers and wheelchair users.

Advantages of Wheel-Side Drive in Electric Buses

1. Space Optimization and Low-Floor Design

• Eliminates mechanical components, enabling ultra-low floor heights and wider aisles.
• Aligns with urban bus trends for accessibility and passenger convenience.

For instance, the structural dimensions of an integrated wheel-side drive axle can reduce floor installation height by approximately 70?mm, achieving a floor clearance as low as 290?mm. This enhanced design meets both interior space and passenger safety requirements.

2. Lightweight Design

• Weight reduction lowers energy consumption by 6% - 8% per 10% mass reduction.
• High-speed motors and integrated systems minimize size and material use.

3. Enhanced Power Performance

• Dual-motor setups reduce individual motor power demands while improving torque output.
• Eliminates main reducers, replacing them with high-ratio helical gear reducers for higher efficiency and durability.

4. Improved Energy Efficiency

• Shorter transmission chains and helical gear reducers boost efficiency by 3%-5% compared to traditional hypoid gears.
• Optimized energy recovery during braking.

5. Design Flexibility

• Frees up chassis space for battery placement (floor or roof), improving weight distribution.
• Modular design supports hybrid, fuel cell, and articulated bus applications. For example, an 18-meter articulated bus, for instance, can be configured with either one or two wheel-side drive axles, offering significant versatility in design and application.

6. Reduced Maintenance Issues

• Avoids common main reducer failures like gear wear and noise.
• Helical gear machining simplifies manufacturing and enhances reliability.

Market Applications of Wheel-Side Drive Systems

BYD

• Pioneered wheel-side drive systems in 2009, now deployed in 8-12m buses globally (50+ countries, 5000+ units).
• Flagship models: 27m K12A double-articulated bus with redundant 4-motor design and dual/four-wheel drive modes.

ZEV Auto

• Independent air suspension reduces weight and achieves ultra-low floors.
• 12m city buses feature triple-axle designs with optimized vibration isolation.

Mercedes-Benz

• eCitaro with wheel-side electric axle (243 kWh battery, 150 km range)
• Next-gen models target 400 kWh batteries to cover 70% of daily routes without charging.

Why This Matters for Bus Manufacturers?

For OEMs and tech partners, wheel-side drive systems unlock:

?Lower operational costs through lightweighting.

?Compliance with stringent urban accessibility mandates.

?A competitive edge in the $50B+ electric bus market.

How we can empower your bus project

To empower bus manufacturers to remain competitive and lead in the decarbonization of public transport, we have introduced advanced distributed wheel-side drive solutions.

These innovations not only shorten project timelines and accelerate both R&D and manufacturing processes but also help reduce overall costs.

Already deployed on (hybrid) electric buses and rubber-tired metros both domestically and internationally, our solutions are designed to deliver superior performance and efficiency in the evolving landscape of sustainable transportation.

Discover our distributed drive e-axle solutions for buses here:?https://brogenevsolution.com/distributed-electric-drive-axle-for-bus/

Read the full text here: https://brogenevsolution.com/electric-bus-powertrain-wheel-side-drive-motor-introduction-and-analysis/

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