Stepped Planetary Gear Unit for Seamless EV Two-Speed Shifting
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Solution Overview
Problem
Existing powertrain systems for electric vehicles lack an efficient two-speed gear unit that can maintain motive power during shifting between gear ratios without interrupting output, and require separate power shifting elements, which complicates the design and increases costs.
Innovation Solution
A gear unit with a stepped planetary gearset, a first gear shifting element, and a second gear shifting element, where either the first sun gear or the first planet carrier is connected to the electric machine, allowing for a two-speed drive with a ratio step of 1.7 to 2.5, and utilizing frictionally engaging or positively engaging shifting elements to enable seamless power shifting without the need for separate shifting elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If separate power shifting elements are used for shifting between gear ratios, then the powertrain can maintain motive power during shifting, but the device complexity increases
Solution Approach 1:
The patent combines the gear shifting function and power shifting function into a single shifting element. The shifting element simultaneously disengages the first gear ratio and engages the second gear ratio while maintaining continuous power transmission through the planetary gearset, eliminating the need for separate power shifting elements and reducing overall system complexity
Solution Approach 2:
The shifting element is designed to perform multiple functions: it acts as both a gear selector (switching between gear ratios) and a power maintaining mechanism (ensuring continuous torque transmission). This multi-functional design allows a single component to replace what would traditionally require multiple specialized components
2Adaptability or versatility
If a two-speed gear unit is implemented with traditional design, then gear ratio switching is possible, but the axial installation space increases
Solution Approach 1:
The planetary gearset is configured with nested components where the second planet gear is positioned within the space defined by the first planet gear and ring gear. The sun gear, planet gears, and ring gears are arranged concentrically, allowing the two-speed mechanism to be compacted into a small axial footprint while maintaining full functionality
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 proposed gear unit achieves a two-speed drive with high efficiency, maintains motive power during shifting, and simplifies the design by integrating shifting elements, reducing the need for separate power shifting elements and optimizing axial installation space.
Implementation Method 1
at least one frictionally engaging shifting element for carrying out power shifts
Data Source
AI summary
A gear unit for a powertrain and a powertrain including a stepped planetary gearset, a first gear shifting element and a second gear shifting element. The stepped planetary gearset has a first sun gear, a first ring gear, a second ring gear, and stepped planet gears rotatably mounted at a first planet carrier. The first ring gear is fixed with respect to rotation to an output shaft of the gear unit. The second ring gear is fixed with respect to rotation to a housing. The first gear shifting element drivingly connects the first sun gear to an electric machine in a closed state, and the second gear shifting element drivingly connects the first planet carrier to the electric machine in a closed state, and one of the two gear shifting elements is in the closed state for driving the output shaft in rotation.