Planetary Stage Spline Layout for Higher Torque and Lower Cost

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Solution Overview

Problem

Existing wind turbine transmissions with a first and second planetary stage face challenges due to the high-stress conditions on the sun gear, requiring high-strength materials that increase production costs and limit stability under load.

Innovation Solution

The arrangement includes a first and second planetary stage with a sun shaft connected to the planet carrier of the second stage via a spline joint, where the spline joint is axially spaced apart from the planet carrier web, allowing for a shorter sun shaft and redistribution of material to the planet carrier, enabling larger spline joints for higher torque transmission.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If the sun shaft is made of high-strength material to withstand stresses, then the strength is improved, but the production costs increase

Engineering Contradiction:

ImprovestrengthVSAvoidproduction costs

Core Design Contradiction:

StrengthVSEase of manufacture

Solution Approach 1:

The patent applies local quality by making only the sun gear (not the entire sun shaft) from high-strength material. The sun gear is the specific component subjected to high stresses during operation, while the sun shaft can be made from less expensive material, thereby reducing production costs while maintaining necessary strength at the critical location.

Inventive Principle:

Principle #3Local quality

2Stability of the object's composition

If the sun shaft diameter is increased to improve stability under load, then the stability is improved, but the diameter is limited by the planet carrier

Engineering Contradiction:

Improvestability under loadVSAvoiddiameter of sun shaft

Core Design Contradiction:

Stability of the object's compositionVSLength of moving object

Solution Approach 1:

The patent resolves the diameter limitation by shifting the load-bearing function to the axial dimension. The spline joint is positioned axially offset from the planet carrier web, allowing the sun shaft to extend axially beyond the planet carrier. This enables increased stability under load through greater axial length of the sun shaft and spline joint without being constrained by the radial diameter of the planet carrier.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Volume of moving object

If the spline joint is positioned inside the planet carrier surrounded by the web, then the compactness is improved, but the sun shaft diameter is limited

Engineering Contradiction:

ImprovecompactnessVSAvoiddiameter of sun shaft

Core Design Contradiction:

Volume of moving objectVSLength of moving object

Solution Approach 1:

The patent inverts the conventional arrangement by positioning the spline joint axially offset from the planet carrier web rather than inside it. Instead of having the web surround the spline joint radially, the spline joint extends axially beyond the web, allowing the sun shaft to have a larger effective length for torque transmission while maintaining a compact radial footprint.

Inventive Principle:

Principle #13The other way round (Inversion)

Data Source

PatentUS20250198467A1Arrangement comprising planetary stages and a spline

Publication Date: 2025.06.19 ZF FRIEDRICHSHAFEN AG

AI summary

An arrangement including a first planetary stage and a second planetary stage. A sun shaft of the first planetary stage is connected to a planet carrier of the second planetary stage for conjoint rotation by a spline joint. A web of the planet carrier is arranged axially between planet gears of the first planetary stage and planet gears of the second planetary stage. The spline joint is axially spaced apart from the web.