Stepped Planetary Gear Unit for Seamless Two-Speed EV Drive
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Solution Overview
Problem
Existing powertrains for electrically driven vehicles lack efficient two-speed gear units that can provide a suitable ratio step and high efficiency without interrupting motive power during gear shifting, and often require separate power shifting elements.
Innovation Solution
A gear unit with a stepped planetary gearset, including a first sun gear, ring gears, and planet gears, along with two gear shifting elements that allow for a two-speed drive by connecting the ring gears to the output shaft in a closed state, enabling a ratio step of 1.7 to 2.5 and high efficiency without separate power shifting elements, 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 for electrically driven vehicles, then the ratio step and efficiency are improved, but the device complexity increases due to the need for multiple shifting elements
Solution Approach 1:
The patent combines the functions of multiple shifting elements into a single integrated shifting element that can selectively connect different ring gears to the output shaft. This merging approach reduces the number of separate components while maintaining the two-speed functionality, thereby improving the ratio step capability without proportionally increasing device complexity
Solution Approach 2:
The single shifting element is designed with multi-functionality to perform multiple tasks: it can connect the first ring gear to the output shaft for one speed ratio, connect the second ring gear for another speed ratio, and potentially engage in power shifting operations. This universal design allows one component to replace what would traditionally require multiple specialized elements
2Ease of operation
If separate power shifting elements are used for gear shifting, then the gear shifting capability is improved, but the device complexity and cost increase
Solution Approach 1:
The patent merges the gear shifting function with the existing shifting element structure. The same shifting element that selects between different ring gears also performs power shifting by engaging with the sun gear or carrier. This combination eliminates the need for separate power shifting elements while maintaining full gear shifting capability
Solution Approach 2:
The shifting element is designed as a universal component that can operate in multiple modes: selective engagement of ring gears for speed ratio changes, and power shifting engagement with the sun gear or carrier. This multi-functionality allows a single element to perform what would traditionally require multiple specialized elements, reducing complexity
3Ease of manufacture
If frictionally engaging shifting elements are used, then the cost is reduced and construction is simplified, but the power transmission efficiency during shifting may be affected
Solution Approach 1:
The frictionally engaging shifting element is designed to maintain continuous power transmission during the shifting process. By using friction engagement rather than positive engagement with disengagement, the system ensures that power flow is never completely interrupted, maintaining efficiency while allowing simpler, more cost-effective friction-based component design
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 enables a two-speed drive with a ratio step of 1.7 to 2.5, achieving high efficiency and seamless power transmission between gears without interrupting motive power, while also providing a cost-optimized design by eliminating the need for a second sun gear and simplifying the construction with frictionally engaging shifting elements.
Implementation Method 1
a stepped planetary gearset (4) with a first sun gear (7), a first ring gear (8a), a second ring gear (8b), and a plurality of stepped planet gears (10)
Implementation Method 2
using either positively engaging or frictionally engaging shifting elements
Data Source
AI summary
A gear unit for a powertrain and gear unit having 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 a plurality of stepped planet gears rotatably mounted at a first planet carrier. The first sun gear is connected to an electric machine. The first planet carrier is fixedly connected to a housing with respect to rotation. The first gear shifting element connects the second ring gear to an output shaft of the gear unit in a closed state, and the second gear shifting element connects the first ring gear to the output shaft of the gear unit in a closed to state, and one of the two gear shifting elements) is in the closed state for driving the output shaft in rotation.