Heavy-Duty Wheel Drive Unit With Multispeed Planetary Gear Train
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Solution Overview
Problem
Existing wheel drive units in heavy-duty vehicles face efficiency losses due to the electric motor being far from the wheels, leading to increased stress on gearbox components and reduced durability, while also occupying valuable space that could be used for batteries.
Innovation Solution
A compact wheel drive unit with a multispeed transmission system, featuring a 3-gears system for optimal performance and efficiency, and a planetary gear train with force balancing to reduce bearing size and weight, allowing for aluminum housings and improved lubrication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a wide gear reduction ratio (20-50) is provided with several reduction stages to compensate for high-speed/low torque conditions, then torque demand at the wheels is satisfied in all situations, but the gearbox size and complexity increase
Solution Approach 1:
The patent applies a variable ratio transmission system where the gear ratio can change during operation. This allows the system to provide high torque multiplication when needed (starting, low-speed conditions) and switch to lower ratios for high-speed cruising, eliminating the need for a single wide-ratio gearbox that would be required to handle all conditions. The dynamic adjustment of gear ratio resolves the contradiction by providing high power when needed without permanently increasing gearbox complexity.
Solution Approach 2:
The transmission system is divided into multiple independent gear stages that can be selectively engaged. Rather than using one large gearbox covering the entire 20-50 reduction range, the system segments the torque multiplication into separate stages, each handling specific operating conditions. This segmentation allows each gear stage to be optimized for its specific function, reducing overall system complexity while maintaining the ability to deliver required torque.
2Power
If high-speed gears are used to achieve wide gear reduction ratio, then torque demand is met, but lubrication problems occur due to centrifugal ejection of oil
Solution Approach 1:
The variable ratio transmission dynamically adjusts gear engagement based on operating conditions. During high-speed cruising, the system disengages high-ratio gears and uses lower ratios, preventing the centrifugal ejection of lubricant that would occur in fixed high-speed gears. This dynamic operation ensures reliable lubrication across all operating conditions while still meeting torque demands when needed.
Solution Approach 2:
The transmission system maintains continuous proper lubrication by ensuring that gears operate within speed ranges where effective lubrication is possible. The variable ratio system prevents intermittent lubrication failure that would occur in fixed-ratio systems by continuously adapting the gear ratio to keep rotational speeds within lubrication-effective ranges, ensuring uninterrupted protective oil film formation on gear surfaces.
3Ease of manufacture
If the electric motor is positioned far from the wheels under the truck cab, then the transmission layout is simplified, but efficiency losses increase and space for batteries is reduced
Solution Approach 1:
The patent integrates the gearbox and differential into a compact unified assembly that is directly mounted to the wheel hub. This nested configuration places the electric motor, transmission, and differential in a tightly integrated package at the wheel, eliminating long propeller shafts and intermediate transmissions. The nesting of components within each other's spatial envelopes achieves both compactness for battery space and direct connection for efficiency.
Solution Approach 2:
The electric motor is positioned with its rotation axis parallel to the wheel shaft axis, representing a dimensional change from the conventional arrangement where the motor axis is perpendicular to the wheel plane. This parallel axis configuration, combined with the integrated gearbox design, allows the powertrain to fit within the wheel well space envelope, achieving both compact integration and direct wheel connection without the efficiency losses of long power transmission paths.
Data Source
AI summary
A wheel drive unit is to be fitted on a chassis of a heavy-duty vehicle. The wheel drive unit has at least one wheel shaft, configured to drive a wheel in rotation, at least one electric motor, capable of generating a torque, a gearbox for transmitting the torque of the motor(s) to the wheel shaft(s) and a transmission system between the electric motor(s) and the gearbox. The transmission system has of a gear train. A rotation axis of the electric motor is parallel to that of the wheel shaft(s).