Analysis of the Wheel-Side Distributed Drive Electric Axles and Its Impact on Electric Bus Performance

The wheel-side distributed drive electric axle system with independent suspension significantly reduces vehicle weight and energy consumption. ZEBs equipped with this system benefit from first-step access, a fully flat floor, and wide aisles, providing an interior layout comparable to a subway. This design maximizes standing space and enhances passenger capacity flexibility.

In this article, we will introduce the basic principles of the wheel-side distributed drive electric axle system, which provides a lighter, more powerful, and wider aisle electric powertrain solution for 8-12 meter (hybrid) electric buses.

1. Basic Introduction to the Wheel-Side Distributed Drive Electric Axle System

• A typical feature of this system is the use of the left and right wheel-side motors, which replace the conventional differential and gearbox. This design directly applies the drive axle torque to the left and right wheels.
• The mechanical assembly of the e-drive system consists of a high-speed wheel-side motor and reducer, achieving high torque in a compact size.
• The motor and its controller for the wheel-side e-drive operate in the same way as other electric and hybrid vehicle motor controllers. The challenge in controlling the system lies in implementing differential speed between the drive axles. Thus, the control strategies and functions differ from those of other electric and hybrid vehicles.

1.1 Three Methods for Driving a Fully Electric City Bus

Currently, there are three main types of e-powertrain architecture for a fully electric city bus:

The distributed wheel-side motor + transmission solution eliminates the need for a differential, or half-shaft, and shortens the transmission chain. This results in higher transmission efficiency, a lighter vehicle, and reduced energy consumption. The compact motor size and wide aisle inside the bus make it suitable for low-floor layouts.

Before in-hub motor technology becomes fully mature, wheel-side distributed drive e-axles remain the best matching solution for battery electric vehicles.

1.2 Basic Structure of the Wheel-Side Distributed Drive Electric Axle

• Independent Suspension System: 4-airbag double wishbone design, low unsprung mass, offering comfort, smoothness, and excellent handling stability.
• Wheel-Side Motor: High torque density and power density. Dual-wheel-side motor drive with strong power output.
• Reducer: Reduces the motor output power to increase torque.
• Motor Controller: Controls the motor to operate at the desired speed, angle, direction, and response time.
• Electronic Components: Includes accelerator pedal sensors, brake pedal sensors, Hall-effect wheel speed sensors, Hall-effect steering angle sensors, roll angle sensors, yaw rate sensors, and controller hardware.

1.3 Working Principle of the Wheel-Side Distributed Drive E-Axle

The vehicle's VCU calculates the total torque demand based on the driver's intent (acceleration or deceleration) and sends this value to the electronic differential system (EDS). The EDS allocates the total torque between the left and right drive motors based on the steering angle, vehicle posture sensors, and road surface traction coefficients. The left and right motor controllers, upon receiving the instructions, convert the energy from the battery to the necessary power for the drive motors, ensuring the vehicle's stability and handling.

1.4 Wheel-Side Motor Operation Modes

• Driving Mode: The battery supplies energy to the drive motor through the motor controller, which then directly drives the wheels.
• Regenerative Braking Mode: The rolling wheels drive the motor (regenerative generation) to charge the battery (energy recovery).

2. Application of the Wheel-Side Distributed Drive E-Axle on Electric Buses

2.1 Solution Advantages

• The 4-airbag independent suspension provides better comfort than rigid axles.
• Eliminates rigid axles and drive shafts, improving transmission efficiency by 5% compared to traditional direct-drive systems.
• For an 8.8-meter electric bus, the weight of the e-powertrain system can be reduced by more than 700 kg; for a 10-meter electric bus, the weight of the e-powertrain system can be reduced by more than 800 kg, enhancing economic benefits.

2.2 Example Applications

• In a city with 200 electric buses using this system for a year, passenger injury rates dropped by around 70%, avoiding serious accidents from falls on stairs.
• Low-floor: Provides easier access for the elderly, children, and people with disabilities.
• Four-airbag Independent Suspension: More stable body, reducing the risk of passenger falling during travel.
• Electronic Differential: Improves stability on slippery surfaces, making driving on wet roads safer.
• Flat-floor Design: 70% of incidents in some companies were related to rear step injuries. The electric bus with this system eliminates the risk of passengers falling from high steps at the rear.
• Small Bus, High Capacity: The e-axle systems allow for a small bus to achieve the same capacity as larger buses. The 8-meter bus has 43% fewer accidents annually than a 10-meter bus. Its smaller size reduces the risk of external collisions in urban areas.

Conclusion

This system offers a lighter, more powerful, and more spacious electric drive solution for 8-12 meter electric buses. It provides passengers with a new experience while effectively reducing vehicle weight and energy consumption. The design includes first-step access, a fully flat floor, and wide aisles.

At Brogen, we provide distributed e-axle solutions for commercial vehicles. Here are the main benefits of our bus powertrain solution:

• Optimized Interior Space – Enables an800 mm wide aisle and a fully flat low-floor design?for enhanced accessibility and passenger comfort.
• Enhanced Maneuverability & Safety – Integrated steering function allows the rear wheels to track the front wheels, significantly reducing right-turn accidents caused by wheel differences.
• Proven Reliability – Features a mature and dependable electronic differential system, with tire replacement mileage exceeding?100,000 km.

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

Business inquiry: [email protected]

We usually respond within 2 business days.