Electric Axle Planetary Differential for Compact Three-Speed Reduction
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Solution Overview
Problem
Existing electric axles face challenges in achieving both high power density and compact packaging due to increased motor rotational speeds, which lead to larger package envelopes and decreased power density.
Innovation Solution
An electric axle system with a planetary reduction differential that includes two directly coupled simple planetary gear sets, allowing for a Ravigneaux three-speed mode planetary gear set to achieve three gear ratio modes in a compact package, enhancing space efficiency and power density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the motor's rotational velocity is increased to achieve higher power density, then the power density increases, but the package envelope size increases and power density decreases
Solution Approach 1:
The patent employs nested planetary gear sets where a first planetary gear set is positioned inside a second planetary gear set, both sharing a common central axis. This nesting arrangement allows multiple gear reduction stages to be compacted into a smaller volume, achieving high output ratios without increasing the package envelope size proportionally
Solution Approach 2:
The patent transitions from a single-stage planetary gear arrangement to a multi-stage nested planetary gear system, adding a radial dimension to the gear arrangement. By stacking planetary gear sets concentrically, the design achieves greater reduction ratios within the same axial space, effectively utilizing three-dimensional space to resolve the volume-power density contradiction
2Speed
If the number of gear passes is increased to achieve greater output ratio, then the output ratio increases, but the size of the electric axle package envelope increases
Solution Approach 1:
The patent merges multiple planetary gear sets into a single integrated transmission unit with a common input shaft and concentric arrangement. By combining several gear reduction stages into one compact nested structure, the design achieves high output ratios without the cumulative volume increase that would result from separate gear boxes or sequential gear stages
Solution Approach 2:
The nested planetary gear sets allow multiple gear passes to be contained within each other, with the first planetary gear set positioned inside the second planetary gear set. This nesting enables the system to achieve compound reduction ratios while maintaining a compact package envelope, as the inner gear set utilizes the internal space of the outer gear set
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system achieves increased compactness and power density by reducing the width and overall axial length of the electric axle, enabling efficient vehicle integration and expanded speed change capabilities.
Implementation Method 1
The planetary reduction differential includes a first planetary gear set directly rotationally coupled to a second planetary gear set
Data Source
AI summary
Methods and systems are provided for an electric axle. The electric axle system includes, in one example, a first electric machine and a planetary reduction differential configured to receive mechanical power from the first electric machine. The planetary reduction differential includes a first planetary gear set directly rotationally coupled to a second planetary gear set. In the electric axle system, a sun gear in the first planetary gear set is directly coupled to an input shaft of the planetary reduction differential.