Stepped Planetary Gear Unit for Seamless Two-Speed EV Shifting
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Solution Overview
Problem
Existing powertrains for electric vehicles lack an efficient two-speed gear unit that can provide a suitable gear ratio step and high efficiency without interrupting motive power during shifting, and often require separate power shifting elements.
Innovation Solution
A gear unit with a stepped planetary gearset and two gear shifting elements, where either the first sun gear or the second sun gear is connected to the electric machine via a gear shifting element, allowing for a two-speed drive with a ratio step of 1.7 to 2.5 and enabling power shifting between gears without interrupting motive power, using either positively engaging or frictionally engaging shifting elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a two-speed gear unit is implemented in an electric vehicle powertrain, then the vehicle can achieve better acceleration and efficiency across different speed ranges, but the device complexity increases due to additional gear shifting elements and mechanisms
Solution Approach 1:
The patent combines the functions of two separate sun gears (first sun gear and second sun gear) into a single stepped planetary gearset. The stepped planet gears have different diameter sections that engage with different sun gears, allowing both speed ratios to be achieved through one integrated gearset rather than two separate planetary gearsets. This merging reduces the number of components while maintaining the two-speed functionality.
Solution Approach 2:
The stepped planet gears serve multiple functions: they engage with the first sun gear to provide one speed ratio, engage with the second sun gear to provide another speed ratio, and their different diameter sections allow a single planet carrier to handle both engagement scenarios. This multi-functionality eliminates the need for separate gearsets for different speed ratios.
2Adaptability or versatility
If separate power shifting elements are used for each transmission ratio stage, then each ratio stage can be shifted independently, but the device complexity and axial installation space requirements increase
Solution Approach 1:
The patent merges the shifting control into a single planetary carrier that can selectively engage with either the first sun gear or the second sun gear through the stepped planet gears. Instead of having separate shifting elements for each sun gear, one planetary carrier with stepped planets provides both engagement paths, reducing the number of shifting elements from two to one.
3Productivity
If a stepped planetary gearset with two sun gears is used, then a ratio step of 1.7 to 2.5 can be achieved, but the axial installation space increases due to the additional sun gear and planet gear structure
Solution Approach 1:
The stepped planet gears are designed with different diameter sections nested concentrically, where one section engages with the first sun gear and the other section engages with the second sun gear. This nested arrangement allows both engagement paths to coexist within the same radial space, minimizing the axial footprint of the gearset.
4Reliability
If frictionally engaging shifting elements are used for power shifting, then seamless power transfer can be achieved during gear shifts, but energy loss increases due to friction
Solution Approach 1:
The patent employs a dynamic shifting mechanism where the planetary carrier is selectively positioned to engage with either the first sun gear or the second sun gear. This dynamic engagement allows for controlled power transfer during shifting, where the friction is applied only temporarily during the transition phase rather than continuously, thereby reducing overall energy loss while maintaining power transfer continuity.
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 solution allows for a compact, cost-optimized powertrain that achieves a two-speed drive with high efficiency and seamless power shifting, reducing the need for separate power shifting elements and saving axial installation space.
Implementation Method 1
The first sun gear and the second sun gear are each in meshing engagement with a first toothed wheel and a second toothed wheel of the stepped planet gears, respectively
Implementation Method 2
Each of the transmission ratio stages can be shifted with the positively engaging shifting element. At least one of the ratio stages can be shifted with the positively engaging shifting element as well as with the frictionally engaging shifting element
Data Source
AI summary
A gear unit includes: a stepped planetary gearset, and first and second gear shifting elements. The stepped planetary gearset has first and second sun gears, a first ring gear and a plurality of stepped planet gears rotatably mounted at a first planet carrier. The first ring gear is connected to an output shaft of the gear unit thus being fixed with respect to rotation relative to it. The first planet carrier is connected to a housing and fixed with respect to rotation relative to it. The first gear shifting element drivingly connects the second sun gear to an electric machine in a closed state, and the second gear shifting element drivingly connects the first sun gear to an electric machine in a closed state. One of the two gear shifting elements is in the closed state for driving the output shaft in rotation.