Bottom Bracket Planetary Gearbox Layout for More Gears in Less Space

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Solution Overview

Problem

Existing bicycle and pedelec gearboxes with planetary designs require significant installation space due to multiple planetary gear sets and shift elements, leading to inefficiencies and increased component loads.

Innovation Solution

A bottom bracket gearbox with three coaxial planetary gear sets and five shift elements, utilizing interlocking brakes and freewheel units, allows for a compact design that achieves at least six gears with reduced component loads and high gearing efficiency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If multiple planetary gear sets are used to implement multiple gears, then the number of available gears increases, but the installation space required increases significantly

Engineering Contradiction:

Improvenumber of gearsVSAvoidinstallation space

Core Design Contradiction:

Adaptability or versatilityVSArea of stationary object

Solution Approach 1:

The patent combines multiple planetary gear sets (first, second, and third planetary gear sets) into a single integrated gearbox unit with shared components. The planetary gear sets are interconnected through common shafts and housings, allowing multiple gears to be achieved within a compact footprint. Specifically, the first planetary gear set includes sun gear, planet gears, and ring gear that share common mounting structures with the second and third planetary gear sets, reducing overall installation space while maintaining gear versatility.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent employs a nested arrangement where planetary gear sets are positioned concentrically and interconnected through shared shafts. The first planetary gear set is arranged with the second planetary gear set in a nested configuration, both sharing common mounting structures. This nesting allows multiple gear mechanisms to occupy overlapping or adjacent spatial volumes, significantly reducing the total installation space required while maintaining the ability to provide multiple gear ratios.

Inventive Principle:

Principle #7Nested doll (Nesting)

2Adaptability or versatility

If multiple shift elements are added to increase the number of gears, then gear versatility improves, but device complexity increases

Engineering Contradiction:

Improvenumber of gearsVSAvoidnumber of shift elements

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent designs shift elements that can control multiple planetary gear sets simultaneously or selectively. The shift elements are configured to engage with multiple gear elements across different planetary gear sets, allowing a single shift element to control multiple gear ratios. This multi-functionality reduces the total number of shift elements needed while maintaining the ability to provide at least six different gear ratios through selective engagement of the first, second, and third planetary gear sets.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The patent incorporates pre-configured engagement paths and predetermined gear ratio sequences through the arrangement of planetary gear sets and shift elements. The gear sets are positioned and interconnected such that shift elements can sequentially engage predetermined gear combinations, allowing for smooth gear transitions without requiring complex real-time calculations or multiple independent shift mechanisms. This preliminary arrangement of gear elements simplifies the shifting mechanism while maintaining gear versatility.

Inventive Principle:

Principle #10Preliminary action

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The compact design minimizes installation space requirements while maintaining high efficiency and flexibility in gear selection, with the option for negative or positive planetary gear sets and integration of torque sensors and electric machines.

Implementation Method 1

three planetary gear sets which are coaxial with the bottom bracket gearbox

Methodology Applied

Scientific EffectGear meshing: Gear

Implementation Method 2

geometric transmission ratio range in the bottom bracket gearbox

Methodology Applied

Scientific EffectMechanical advantage: Mechanical Advantage

Implementation Method 3

five shift elements for implementing at least six gears

Methodology Applied

Scientific EffectFriction: Friction

Implementation Method 4

interlocking brakes and freewheel units

Methodology Applied

Scientific EffectMechanical interlocking: Mechanical Fastener

Data Source

PatentUS20250223005A1Bottom Bracket Transmission with a Planetary Design for a Bicycle or Pedelec

Publication Date: 2025.07.10 ZF FRIEDRICHSHAFEN AG

AI summary

A bottom bracket gearbox includes a crank axle and a gearbox output shaft. The crank axle is connected to a second element of the first planetary gear set and connectable to a third element of the second planetary gear set via a fourth shift element and a second shaft. The gearbox output shaft is connected to a first element of the first planetary gear set and to a first element of the third planetary gear set. A third element of the first planetary gear set is connected to a second element of the second planetary gear set via a first shaft. A first element of the second planetary gear set is connected to a second element of the third planetary gear set via a third shaft. Two elements of the third planetary gear set are connectable via a fifth shift element to interlock the third planetary gear set.