Planetary Bottom Bracket Gearbox With Fewer Shifting Elements
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Solution Overview
Problem
Existing bicycle and pedelec bottom bracket gearboxes require high construction effort and do not achieve optimal efficiency and compactness, as they often rely on complex gearshift mechanisms with multiple components and shifting elements.
Innovation Solution
A bottom bracket gearbox with a planetary design featuring two planetary gear sets and three shifting elements, utilizing a simple and compact structure with only four additional shafts for mechanical connection, allowing for efficient gear shifting and low component loads through the use of brakes and freewheels, and optionally incorporating a torque sensor and electric machine for enhanced control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a complex gearshift mechanism with multiple components is used, then more gear stages can be achieved, but the construction effort and device complexity increase
Solution Approach 1:
The patent combines multiple gear shifting functions into a single planetary gear set. The first and second gear shift groups are integrated into one planetary gear structure with shared elements, reducing the total number of components while maintaining multiple gear stages. This merging approach achieves versatile gear ratios without proportionally increasing construction effort.
Solution Approach 2:
The planetary gear set is designed with multi-functional elements that serve multiple purposes. The third element can be locked via different shafts and shift elements depending on the desired gear stage, allowing a single component to perform multiple gear shifting functions. This universality reduces the need for separate dedicated components for each gear stage.
2Loss of energy
If multiple planetary gear sets are used to achieve geometric gear ratio series, then gear efficiency improves, but the number of shafts and components increases
Solution Approach 1:
The patent uses only two planetary gear sets instead of three or more, achieving the geometric gear ratio series through optimized design of these two sets. The gear shift groups are merged within the planetary structure, reducing the total shaft count to just four additional shafts while maintaining high gear efficiency through the geometric progression of ratios.
Solution Approach 2:
The transmission is segmented into a multi-stage main gear and separate gear shift groups within the planetary set. This segmentation allows the geometric gear ratio series to be achieved in the main gear while the shift groups provide additional ratio changes, distributing the complexity across functional segments rather than requiring multiple complete planetary sets.
3Adaptability or versatility
If more shifting elements are added to increase gear shifting flexibility, then adaptability improves, but component complexity and construction effort increase
Solution Approach 1:
The third element of the planetary gear set serves multiple functions by being lockable through different shafts and shift elements. This universal element can engage different gear stages depending on which shift element is activated, providing gear shifting flexibility without requiring a separate dedicated element for each gear stage.
Solution Approach 2:
The first and second gear shift groups share common elements within the planetary gear structure. By merging these shift groups and using shared elements that can be locked through different mechanisms, the patent achieves flexible gear shifting with fewer total shifting elements compared to having separate independent shift groups.
Data Source
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AI summary
A planetary bottom bracket gearbox for a bicycle or pedelec (1) is proposed, comprising a gearbox input shaft (WAn) as the drive, a gearbox output shaft (WAb) as the output, a multi-stage main gearbox (3), and at least one gearbox shift group (4). The gearbox shift group (4) has two planetary gear sets (RS1, RS2) and three shift elements (B1, B2, K1I, K1II, K1III, K1IV, K1V, K1VI). A second element of a first planetary gear set (RS1) is connected to a first shaft (W1), the first shaft (W1) being connected to the gearbox input shaft (WAn) or, on the output side, to the main gearbox (3). A first element of the first planetary gear set (RS1) is connected via a fourth shaft (W4) to a first element of the second planetary gear set (RS2), and a third element of the first planetary gear set (RS1) is connected via a second shaft (W4). (W2) and can be fixed via a first switching element (B1) designed as a brake,wherein the third element of the first planetary gear set (RS1) is connected via the second shaft (W2) to a second element of the second planetary gear set (RS2), wherein a third element of the second planetary gear set (RS2) can be locked via a third shaft (W3) and a second switching element (B2) designed as a brake, and wherein a fifth switching element (K1I, K1II, K1III, K1IV, K1V, K1VI) designed as a clutch or freewheel is provided for connecting two of the four shafts (W1, W2, W3, W4) to lock the first planetary gear set (RS1) and the second planetary gear set (RS2). Furthermore, a bicycle or pedelec (1) with a bottom bracket gearbox is proposed.