In-line Two-stage Planetary Gear Drive for Compact Electric Powertrain
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Solution Overview
Problem
Existing electric drive vehicles face challenges in achieving a compact powertrain configuration that provides high gear reduction without compromising radial and axial packaging space, which affects the placement of other wheel end components like brakes and suspension.
Innovation Solution
An electric drive unit utilizing an in-line, two-stage planetary gear drive with a single floating ring gear, where the first and second stage gear sets are driven by the motor output shaft, allowing for a compact design by sharing a common ring gear and optimizing gear sizes for varied reductions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If multiple gear sets are used to achieve high gear reduction, then the gear reduction ratio is improved, but the axial and radial packaging space is increased
Solution Approach 1:
The patent combines two stage gear sets into a single integrated planetary gear unit where the first and second planet carriers are merged into one common carrier, and the first and second ring gears are merged into one common ring gear. This merging allows the achievement of high gear reduction ratios through the compound planetary arrangement while significantly reducing the axial and radial space required compared to using separate gear sets.
Solution Approach 2:
The patent employs a nested configuration where the first sun gear and second sun gear are arranged concentrically, with the first planet gears meshing with the first sun gear and the second planet gears meshing with the second sun gear, all within a single common ring gear. This nesting of multiple gear elements within a compact radial arrangement enables high gear reduction in a minimal radial footprint while the shared common carrier provides axial compactness.
2Power
If electric motor and gear box are oriented at right angle to wheel shaft, then gear reduction is achieved, but packaging of brake and suspension components is adversely affected
Solution Approach 1:
Instead of orienting the motor and gear box at a right angle to the wheel shaft as in conventional arrangements, the patent inverts the configuration by aligning the motor output shaft and wheel shaft coaxially. The planetary gear unit is arranged in-line between the motor output shaft and the wheel shaft, with all rotation axes parallel to each other and to the wheel shaft axis. This inverted linear arrangement frees up the radial and axial space that would otherwise be occupied by angled gear sets, providing adequate packaging space for brake and suspension components.
3Volume of moving object
If a compact planetary gear design is used, then radial and axial space is reduced, but achieving high gear reduction becomes more difficult
Solution Approach 1:
The patent utilizes parameter changes in the planetary gear configuration, specifically varying the number of planet gears (first and second plurality of planet gears), the tooth counts of the sun gears and ring gears, and the arrangement of multiple planet carriers to achieve different gear reduction ratios. By changing these parameters within the compact single-stage planetary structure, a wide range of high gear reductions can be achieved without increasing the radial and axial dimensions of the gear unit.
Data Source
Figure 1~3
AI summary
An electric drive unit (10) for a vehicle wheel (12) includes an electric motor (14) that powers a planetary drive (16) having a first stage gear set (40) and a second stage gear set (42). Each of the first and second stage gear sets includes a sun gear (44) that is driven by a motor output shaft (18). Each of the first and second stage gear sets also includes a plurality of planet gears (46) that are in meshing engagement with a respective one of the sun gears. The first and second stage gear sets share a common ring gear (54). A planet carrier (62) of the second stage gear set provides driving output to a wheel shaft (22) that drives the vehicle wheel (12).