Electric Axle Planetary Layout for Compact Multi-Speed Packaging
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Solution Overview
Problem
Existing electric axles face challenges in achieving space efficiency and power density due to multiple parallel shafts and idling gears, leading to bearing, mesh, and windage losses, as well as packaging constraints from wide differentials.
Innovation Solution
A multi-speed electric axle system with a mode planetary gear set and a differential meshed planet compound planetary gear set, eliminating unnecessary shafts and allowing for a compact, power-dense design by using concentric arrangements and mode clutches for efficient gear ratio modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple parallel shafts and idling gears are used in multi-speed transmissions, then gear ratio modes can be achieved, but packaging space increases and power density decreases
Solution Approach 1:
The patent combines multiple planetary gear sets into a single integrated structure where gear sets share common elements (sun gears, planet carriers, ring gears). This merging eliminates the need for separate parallel shafts and idling gears, achieving multiple gear ratio modes within a compact volume while maintaining adaptability.
Solution Approach 2:
The patent employs nested planetary gear sets where one planetary gear set is positioned inside another, with inner planet gears meshing with outer planet gears. This nesting arrangement allows multiple gear ratios to be achieved within a compact radial space, eliminating the need for multiple parallel shafts and reducing overall packaging volume.
2Adaptability or versatility
If all gearing is meshed but torque is only transmitted through a portion of gears in certain modes, then gear ratio modes are achieved, but bearing, mesh, and windage losses increase
Solution Approach 1:
The patent uses a mode clutch that dynamically engages and disengages specific planetary gear sets based on the desired gear ratio mode. This dynamic switching allows torque to be transmitted only through the actively engaged gear set, eliminating energy losses in idle gears while maintaining the ability to achieve multiple gear ratio modes.
Solution Approach 2:
The planetary gear sets are designed to be multi-functional, where the same gear set can serve as an active torque-transmitting element in one mode and be disengaged in another mode. The mode clutch enables universal operation across different gear ratio modes while minimizing energy losses by engaging only the necessary components.
3Adaptability or versatility
If wide differentials are used, then differential functionality is achieved, but packaging constraints increase
Solution Approach 1:
The patent merges the differential functionality with the planetary gear set structure by positioning the differential within the same radial space as the planetary gears. This integration eliminates the need for separate wide differential housing, reducing packaging constraints while maintaining full differential functionality.
Solution Approach 2:
The differential is nested within the planetary gear set structure, with differential components positioned inside the outer diameter of the planetary gears. This nesting arrangement achieves compact packaging by utilizing the existing radial space, eliminating the need for wide differentials while maintaining differential functionality.
Data Source
AI summary
Methods and systems are provided for an electric axle. The electric axle system includes, in one example, an electric machine and a multi-speed transmission that is rotationally coupled to the electric machine and rotationally coupled to two output shafts. The transmission includes a differential rotationally coupled and positioned coaxial to a mode planetary gear set. In the electric axle system, the mode planetary gear set is a meshed planet compound planetary gear set and a mode clutch in the transmission is configured to selectively shift the mode planetary gear set between a first mode and a second mode.