Planetary EV Transmission With Four Ratios and Small Shift Steps
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Solution Overview
Problem
Existing transmissions for electric heavy-duty vehicles face challenges in providing a compact design with a wide range of gear reduction ratios to ensure startability and efficiency at cruising speeds, particularly for vehicles with high gross combination weight, leading to large steps between gear ratios and power drops during shifting.
Innovation Solution
A transmission design featuring a planetary gear system with a single ring gear and double sun gears, allowing independent engagement with an input component and a fixed member, enabling at least four gear ratios with small steps between them, and a compact, cost-effective configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a transmission provides a wide range of gear reduction ratios for heavy-duty electric vehicles, then startability and cruising efficiency are improved, but the device complexity increases and space requirements increase
Solution Approach 1:
The transmission is segmented into two independent planetary gear sets, each capable of providing different gear ratios. The first planetary gear set provides a first gear ratio while the second planetary gear set provides a second gear ratio, allowing the transmission to offer multiple gear options without requiring a single complex gear train. This segmentation enables the transmission to achieve adaptability across different operating conditions while maintaining manageable complexity in each individual gear set.
Solution Approach 2:
Each planetary gear set is designed to be multi-functional, capable of operating independently to provide different gear ratios. The first and second planetary gear sets can each function as the primary reduction mechanism depending on operating conditions, with their respective clutch arrangements enabling selective engagement. This universality allows the transmission to adapt to various vehicle loads and speeds without requiring additional specialized components.
2Volume of moving object
If a transmission is designed to be compact for electric vehicle space constraints, then battery mounting space is improved, but the ability to provide sufficient gear reduction ratios deteriorates
Solution Approach 1:
The two planetary gear sets are arranged in a nested or closely integrated configuration where the second planetary gear set is positioned adjacent to and partially overlapping with the first planetary gear set. The planet carriers and gear components are arranged to maximize space utilization, with shared support structures and common mounting points. This nesting approach allows the transmission to provide multiple gear ratios through compact arrangement rather than requiring linear extension of gear trains.
Solution Approach 2:
Instead of arranging gear components primarily in a linear sequence along the power flow path, the design utilizes three-dimensional spatial arrangement by stacking planetary gear sets vertically and arranging planet gears in multiple radial layers. This dimensional approach allows multiple gear reduction stages to be packed into a smaller overall volume while maintaining the necessary gear ratio ranges for both startability and cruising efficiency.
3Adaptability or versatility
If gear ratios are spaced far apart to cover a wide range, then adaptability across different speeds is improved, but power drops during gear shifting increase
Solution Approach 1:
Both planetary gear sets are pre-configured and ready for engagement before a gear shift is required. The clutch arrangements for the first and second planetary gear sets are designed to enable rapid selection between different gear ratios without requiring intermediate steps or complex sequencing. This preliminary preparation of multiple engagement paths allows for smoother transitions and reduces the duration and magnitude of power drops during gear shifting events.
4Adaptability or versatility
If multiple planetary gear sets are added to provide more gear ratios, then gear ratio range is improved, but manufacturing cost increases
Solution Approach 1:
The first and second planetary gear sets are designed with homogeneous component types and similar structural characteristics, using the same basic planetary gear configuration, comparable gear tooth profiles, and analogous support structures. This homogeneity allows for standardized manufacturing processes, shared tooling, and bulk procurement of common components, thereby reducing the manufacturing cost increase that would normally accompany the addition of multiple gear sets. The repeated use of proven design elements across both gear sets simplifies production while maintaining the ability to provide multiple gear ratios.
Data Source
AI summary
A transmission for a vehicle providing at least four gear ratios, comprising an input component drivingly connected to a prime mover, such as an electric motor, and a planetary gear system, comprising a first sun gear, a second sun gear, a single ring gear, and a single planet gear carrier carrying a first set of planet gears in meshing engagement with the first sun gear and a second set of planet gears in meshing engagement with the second sun gear. The ring gear is selectively engageable with one of the input component and a fixed member of the transmission. Both the first and the second sun gears are selectively engageable with the input component, and at least one of the first and second sun gears is selectively engageable with the fixed member.