Coaxial Dual-Motor Drive Unit With Planetary Torque Vectoring
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Solution Overview
Problem
Existing electric drive units for motor vehicles struggle to achieve a balanced torque distribution while maintaining high torque and efficiency, especially during torque vectoring and single-engine operation.
Innovation Solution
The electric drive unit incorporates a differential transmission with a superimposed planetary gear set and switch units to connect the ring gear to the differential shafts or housing in a manner fixed against rotation, allowing for advanced torque distribution and vectoring capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a torque distribution device with multiple planetary gear sets is used, then torque distribution capability is improved, but device complexity increases
Solution Approach 1:
The patent implements a nested planetary gear configuration where a second planetary gear set is positioned inside the first planetary gear set, sharing a common center. The second sun gear is surrounded by the first planetary gears, and the second planetary gears are nested within the annular space between the first ring gear and the second ring gear. This nesting arrangement enables complex torque distribution functionality while minimizing the overall footprint and reducing structural complexity compared to separate gear sets.
Solution Approach 2:
The dual planetary gear system with two electric engines is designed to perform multiple functions: torque distribution between left and right wheels, torque vectoring for yaw moment generation, and adaptable torque splitting ratios. The switch units enable the system to operate in multiple modes (differential mode, locked mode, torque vectoring mode) using the same hardware configuration, achieving versatility without proportionally increasing device complexity.
2Force
If high torques are implemented through planetary gear multiplication, then drive torque is improved, but drive power loss increases
Solution Approach 1:
The patent employs dynamic torque distribution where the two electric engines can independently adjust their torque output based on real-time driving conditions. The switch units dynamically reconfigure the torque flow paths, allowing the system to optimize the balance between torque multiplication and efficiency. During high-torque requirements, the planetary gears provide mechanical multiplication; during efficiency-critical phases, the system can bypass excessive gear stages or operate in direct-drive configurations.
Solution Approach 2:
The system changes operational parameters by varying the torque contribution ratios of the two electric engines and adjusting the engagement state of the switch units. This allows dynamic modification of the effective gear ratio and torque transmission path, optimizing the balance between achieving high drive torque and minimizing energy losses in the transmission system.
3Adaptability or versatility
If a second electric engine is added for torque distribution, then torque vectoring capability is improved, but device complexity and cost increase
Solution Approach 1:
The second electric engine is nested coaxially within the first electric engine, with the second stator positioned inside the first stator and the second rotor inside the first rotor. This nested arrangement allows both engines to share the same spatial envelope, reducing the overall axial length and radial dimensions. The shared planetary gear set further reduces complexity by eliminating redundant transmission components that would otherwise be required for each engine.
4Adaptability or versatility
If switch units are added to connect ring gear to differential shafts, then torque distribution flexibility is improved, but device complexity increases
Solution Approach 1:
The switch units are merged with the existing planetary gear components and differential mechanism. The switching elements are integrated into the torque flow paths of the planetary gears, allowing the same mechanical structures to serve both as torque transmission elements and as switching actuators. This reduces the number of separate switching mechanisms required and simplifies the overall control architecture.
Data Source
AI summary
An electric drive unit includes a first electric engine having a first rotor, a second electric engine having a second rotor, and a transmission unit having a differential transmission with exactly three first shafts arranged coaxially with one another. The three first shafts are a sum shaft to which the first rotor is connected such that torques provided by the first rotor can be introduced into the transmission unit via the sum shaft, a first differential shaft coupled to a first vehicle wheel such that torques can be discharged from the transmission unit and transmitted to the first vehicle wheel via the first differential shaft, and a second differential shaft coupled to a second vehicle wheel such that torques can be discharged from the transmission unit and transmitted to the second vehicle wheel via the second differential shaft.