Power Split Transmission Reducing Reactive Power Losses

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Solution Overview

Problem

Existing continuously variable power-split transmissions face challenges due to high design complexity and reactive power losses, leading to inefficiencies in power split operations.

Innovation Solution

A continuously variable power-split transmission design featuring a first planetary gearset with four shafts, connected via shifting elements to a second planetary gearset and a variator, allowing for a structurally simple, cost-effective, and space-saving configuration with reduced reactive power flows, enabling efficient operation across multiple driving ranges.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If a conventional power-split transmission design is used, then the transmission can achieve power splitting functionality, but the design complexity becomes high and reactive power losses increase

Engineering Contradiction:

Improvedesign complexityVSAvoidreactive power losses

Core Design Contradiction:

Device complexityVSLoss of energy

Solution Approach 1:

The transmission is divided into two independent planetary gear sets (first and second planetary gear sets) with distinct functions. The first planetary gear set handles a specific gear ratio range while the second handles another range, allowing each set to be optimized independently and reducing overall system complexity compared to a single complex gear set.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A variable ratio mechanism (VRM) is introduced as an intermediary component between the input shaft and the planetary gear sets. This VRM continuously varies the transmission ratio within a limited range, enabling the planetary gear sets to operate at optimal speeds and reducing reactive power flows while maintaining smooth power transmission.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Adaptability or versatility

If multiple planetary gear sets are used to achieve four driving ranges, then the transmission ratio range is improved, but the structural complexity and space requirements increase

Engineering Contradiction:

Improvedriving rangesVSAvoidstructural complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

Each planetary gear set is designed to serve multiple functions: they can operate independently to provide different gear ratios, work in combination for extended ratio ranges, and accommodate both forward and reverse travel directions through integrated clutch mechanisms, reducing the need for additional specialized components.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The planetary gear sets are arranged in a nested or closely integrated configuration where components such as shafts, carriers, and gears from the first planetary gear set are spatially related to and interact with components of the second planetary gear set, maximizing space utilization and reducing overall transmission size.

Inventive Principle:

Principle #7Nested doll (Nesting)

3Adaptability or versatility

If multiple planetary gear sets are used to achieve four driving ranges, then the transmission ratio range is improved, but the installation space requirement increases

Engineering Contradiction:

Improvetransmission ratio rangeVSAvoidinstallation space

Core Design Contradiction:

Adaptability or versatilityVSArea of stationary object

Solution Approach 1:

Inventive Principle:

Principle #7Nested doll (Nesting)

Solution Approach 2:

The transmission design utilizes three-dimensional spatial arrangement of planetary gear sets, shafts, and clutches, allowing components to be positioned in multiple dimensions (radial, axial, and circumferential) to achieve compact packaging while maintaining the required transmission ratio range and operational versatility.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Data Source

PatentEP3707411B1Power split continuously variable transmission with at least four travel ranges

Publication Date: 2023.01.11 ZF FRIEDRICHSHAFEN AG

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AI summary

The invention relates to a power split continuously variable transmission (3) which has at least four travel ranges and within which the gear ratio of the power split transmission (3) is continuously variable in the region of a variator (5). A first planetary gear set (P1) which comprises multiple shafts (W11 to W14) can be operatively connected to an additional planetary gear set (P2) which has multiple shafts (W21 to W23) via multiple shift elements (K1 to K4), said additional planetary gear set being operatively connected or connectable to a transmission output shaft (6). According to the invention, the first planetary gear set (P1) comprises four shafts (W11 to W14) and is operatively connected or can be operatively connected to a transmission input shaft (7) and a first shaft (8) of the variator (5) via a first shaft (W11). Additionally, the first planetary gear set (P1) is operatively connected to a second shaft (9) of the variator (5) via a second shaft (W12) while the first planetary gear set (P1) is coupled to shift element halves (10, 11) of two shift elements (K1, K3) via a third shaft (W13) and to a shift element half (12) of an additional shift element (K2) via a fourth shaft (W14).