Stepped Planetary Gear Transmission for Electric Drive Trains

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Solution Overview

Problem

Existing electric drive systems for vehicle drive trains lack efficient gear shifting mechanisms that provide high efficiency and compactness, often requiring separate components like ring gears and parking locks, and do not offer optimal gear ratios and power shiftable capabilities.

Innovation Solution

The electric drive system incorporates a stepped planetary gear set with two input shafts and an output shaft, utilizing shift elements like multi-disk clutches and constant-mesh shift elements to achieve high efficiency gear shifting, eliminating the need for a ring gear and providing power shiftable gears, including a direct gear with 100% efficiency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If a conventional transmission system is used, then the structure is simple, but the gear shifting efficiency is low and the system size is large

Engineering Contradiction:

Improvegear shifting efficiencyVSAvoidtransmission system structure

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The patent merges the ring gear and parking lock into a single integrated component. The ring gear serves dual functions: as a gear element in the planetary gear set and as a parking lock when engaged with the housing. This eliminates the need for a separate parking lock component, reducing device complexity while maintaining high gear shifting efficiency through the compact planetary gear arrangement.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The ring gear is designed with multi-functionality, serving both as a gear element for power transmission in the planetary gear set and as a parking lock mechanism. When the ring gear engages with the housing, it provides the parking lock function, eliminating the need for a dedicated parking lock component and reducing overall system complexity.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Device complexity

If separate components like ring gear and parking lock are used, then the system is reliable, but the system size and complexity increase

Engineering Contradiction:

Improvenumber of componentsVSAvoidsystem reliability

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The ring gear and parking lock are merged into a single component, reducing the number of parts while maintaining reliability. The integrated design ensures that the parking lock function is achieved through the same robust gear element that provides power transmission, eliminating potential failure points associated with additional components and their connections.

Inventive Principle:

Principle #5Merging (Combining)

3Adaptability or versatility

If fixed gear ratios are used, then the manufacturing is simple, but the adaptability to different driving conditions is limited

Engineering Contradiction:

Improvegear ratio adaptabilityVSAvoidtransmission manufacturing

Core Design Contradiction:

Adaptability or versatilityVSEase of manufacture

Solution Approach 1:

The transmission system incorporates a planetary gear set that enables variable gear ratios through dynamic engagement of different clutch elements. The system can shift between fixed gear ratios (first gear ratio when first clutch is engaged, second gear ratio when second clutch is engaged) and provides adaptability to different driving conditions while maintaining manufacturing simplicity through the standardized planetary gear architecture.

Inventive Principle:

Principle #15Dynamics

4Ease of operation

If power shiftable gears are implemented, then the operational flexibility is improved, but the drag losses increase

Engineering Contradiction:

Improvepower shiftable capabilityVSAvoiddrag losses

Core Design Contradiction:

Ease of operationVSLoss of energy

Solution Approach 1:

The patent replaces traditional mechanical gear shifting mechanisms with a planetary gear set controlled by clutch elements. This allows for power shiftable gears where the gear ratio can be changed while power is being transmitted, improving operational flexibility. The direct gear configuration (1:1 ratio) eliminates drag losses by providing a direct mechanical connection without gear intervention, achieving 100% efficiency in that mode.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentUS11642950B2Transmission for an electric drive or drive train of a vehicle, electric drive and drive train

Publication Date: 2023.05.09 ZF FRIEDRICHSHAFEN AG

AI summary

A transmission (1) for an electric drive of a vehicle includes a first input shaft (10), a second input shaft (11), an output shaft (12), two shift elements (3, 4) for connecting the transmission (1) to an electric machine of the electric drive, and a planetary gear set (5) configured as a stepped planetary gear set. A first sun gear (5.1) of the planetary gear set (5) is rotationally fixed to the first input shaft (10). A second sun gear (5.2) of the planetary gear set (5) is rotationally fixed to the second input shaft (11). A ring gear (5.5) of the planetary gear set (5) is fixed at a rotationally fixed component (0) of the transmission (1). A planet carrier (5.6) of the planetary gear set (5) is rotationally fixed to the output shaft (12). A first shift element (3) is configured for connecting the first input shaft (10) to the electric machine of the electric drive. A second shift element (4) is configured for connecting the second input shaft (11) to the electric machine of the electric drive.