Integrated Electric Bus Powertrain Axle Assembly Design
Integrated Electric Bus Powertrain Axle Assembly Design Introduction to Electric Bus Powertrain Development Electric buses have increasingly been recognized worldwide as a leading direction in EV development. As the consumption of non-renewable resources accelerates, the automotive industry’s shift toward electrification is becoming even more pronounced. However, due to current limitations in energy storage technology, electric vehicles continue to lag behind traditional vehicles in areas such as driving range, battery lifespan, and charging convenience. Consequently, pure battery electric buses (BEBs) tailored to specific routes and operating conditions are at the forefront of pilot programs. In recent years, the electrification of public transportation fleets in major cities around the world has gained significant momentum. With substantial investments flowing into the pure electric bus sector, it is critical to harness emerging technologies to strengthen product competitiveness. Among these advancements, the integration of electric motor and drive axle design has notably enhanced the performance of electric buses and has become a key focus in EV safety development. Overview of Integrated Electric Bus Powertrain Axle Assembly Traditional bus powertrains consist of an engine, transmission, driveshaft, and axle assemblies. As the electric bus powertrain industry continues to evolve, many manufacturers initially adopted transitional solutions — replacing the internal combustion engine with an electric motor while largely retaining the traditional mechanical layout, as illustrated in Figure 1. However, this approach introduces several challenges: Low transmission efficiency: Overall system efficiency remains below 80%. Poor system integration: The design conflicts with the industry’s ongoing lightweighting initiatives. Limited regenerative braking performance: Due to the inherent limitations of traditional bevel gear axles, brake energy recovery rates are typically below 30%. The new generation electric bus powertrain layout proposed in this paper effectively overcomes these shortcomings (Figure 2). In this new design, the electric motor is fully integrated into the drive axle assembly, eliminating the need for separately mounted motors, suspension components, and driveshafts within the vehicle frame. This integrated configuration simplifies vehicle layout and installation. The suspension system mounts directly to the axle housing, and the battery packaging is optimized, significantly improving internal space utilization. Nevertheless, engineering challenges remain. Precisely determining the torque axis is complex due to factors such as vehicle and drivetrain layout, packaging constraints, and the mechanical characteristics of rubber isolators, all of which affect the compression-to-shear stiffness ratio and complicate accurate positioning of the fore-aft mounting centers along the torque shaft. System Design of the Integrated Electric Bus Powertrain Axle Assembly Taking an 8.5-meter pure electric bus as a design example: Current mainstream design: Uses a low-speed, permanent magnet synchronous, water-cooled electric motor. Max power: 300 kW Max torque: 2070 Nm Speed: 4000 rpm Axle load: 8 tons Gear ratio: 5.857 Motor weight: 550 kg Driveshaft weight: 40 kg Maximum wheel driving torque: 2070 × 5.857 = 12100 Nm The suspension system’s natural frequency is below 30 Hz. New high-speed design: Introduces a high-speed permanent magnet synchronous, water-cooled motor: Power: 205 kW Torque: 500 Nm Max speed: 12,000 rpm Motor weight: 102 kg Axle weight: 580 kg (with no driveshaft required) Gear ratio: 24.8 Maximum wheel driving torque: 500 × 24.8 = 12400 Nm In traditional axles, the engine layout perpendicular to the driving direction necessitates the use of bevel gears to redirect power. Bevel gear manufacturing limitations mean that convex and concave gear sides have different accuracies. During regenerative braking, if over 30% of braking energy is recovered, the concave gear side’s insufficient precision can cause gear surface damage or even failure. To address this, the new solution arranges the motor parallel to the vehicle’s driving direction, eliminating the need for bevel gears. All gears are cylindrical gears, which are easier to design and manufacture with high precision, improving durability and supporting more efficient brake energy recovery. Weight Comparison Category Weight (kg) Traditional pure electric design 300 + 550 + 40 = 890 kg Integrated axle motor design 102 + 580 = 682 kg Weight saving 890 – 682 = 208 kg Application of Integrated Electric Bus Powertrain Axle Assembly By integrating the motor and axle into a unified powertrain system, there is no longer a need to reserve separate space for the motor. This design reduces the rear suspension space requirements, as shown below, and significantly improves passenger cabin space by increasing the distance between the front and rear doors. Performance Comparison Between Integrated and Traditional Electric Bus Powertrains The integrated electric bus powertrain offers the following advantages over traditional designs: Higher system integration:The axle self-assembles with the powertrain, simplifying vehicle layout and improving transmission efficiency. Enhanced regenerative braking:Brake energy recovery capacity can reach up to 100%. Significant weight reduction:Lightweighting of approximately 208 kg for an 8.5-meter electric bus. Improved vibration isolation and vehicle stability:Experimental tests confirm enhanced ride quality and comfort. Conclusion This study explores an innovative electric bus powertrain layout that significantly improves electric vehicle performance. Through ultra-short rear suspension designs and system lightweighting, the proposed integrated axle motor assembly enhances vehicle energy efficiency (EKG indicators) and extends the continuous driving range. The results demonstrate higher transmission efficiency, superior regenerative braking capabilities, and reveal the future electrification trends for heavy-duty vehicles. Discover our integrated electric bus powertrain (electric bus axle) here: https://brogenevsolution.com/electric-axle-for-bus/ Business inquiry: contact@BrogenEVSolution.com Or you can complete the table below to get in touch with us. 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