Bicycle Drive Device Downshift Control
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Solution Overview
Problem
Existing bicycle drive systems with electric motors and manual transmissions face challenges in reducing wear during gear downshifts due to high actuation and transmission forces.
Innovation Solution
A drive device with a gearbox, crankshaft, and electric machine that uses sensors to detect pedal crank angle, crankshaft speed, output shaft speed, and rotor shaft speed to control the gear downshift by adjusting the current supply to the electric machine, reducing forces and wear during gear changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If gear downshifting is performed in conventional bicycle drive systems, then gear ratio change is achieved, but high actuation and transmission forces cause increased wear
Solution Approach 1:
The control device reduces current supply to the electric machine before a downshift is initiated, preparing the system by lowering rotor shaft speed in advance. This preliminary speed reduction creates favorable conditions for the subsequent gear engagement, allowing the downshift to occur at lower forces between gear components.
Solution Approach 2:
The invention changes the operational parameters of the electric machine by dynamically adjusting current supply based on gear shifting requirements. During downshift preparation, current is reduced to lower rotor speed; during execution, current is increased to maintain crankshaft speed. This parameter modulation enables force-reduced gear transitions.
2Speed
If the electric machine maintains constant current supply during downshifting, then crankshaft speed is maintained, but actuation forces increase and cause wear
Solution Approach 1:
The control device applies periodic modulation to the electric machine's current supply during the downshift process. Current is reduced in specific phases (before and during engagement) and increased in other phases (after engagement), creating a rhythmic control pattern that manages forces while maintaining overall speed stability.
Solution Approach 2:
The system transitions from static constant current supply to dynamic current modulation. The control device continuously adjusts electric machine current based on real-time gear shifting state, enabling adaptive force management that protects gear components while maintaining crankshaft speed within acceptable ranges.
3Force
If current supply to the electric machine is reduced during downshifting, then actuation forces are reduced, but crankshaft speed may fluctuate
Solution Approach 1:
The control device monitors sensor data including crankshaft speed, rotor shaft speed, and gear position, then uses this feedback to adjust electric machine current supply in real-time. This closed-loop control ensures that when current is reduced to lower forces, the system responds by modulating current to maintain crankshaft speed within target ranges.
Solution Approach 2:
The electric machine acts as an intermediary between the cyclist's pedaling input and the gear system. By controlling the electric machine's current, the system mediates the force transmission, allowing smooth transitions that protect gear components while maintaining overall drive system stability and speed.
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 solution enables low-wear downshifting by reducing actuation and transmission forces, ensuring smooth gear transitions and extended component lifespan.
Implementation Method 1
an electric machine (7) with a rotor shaft (8) for transmitting drive power from the electric machine into the gearbox (2)... means for detecting a rotor shaft speed and generating corresponding sensor data... control a downshift from a currently engaged gear to a lower gear depending on this sensor data by energizing the electric machine (7)
Implementation Method 2
means for detecting a pedal crank angle and a crankshaft speed and generating corresponding sensor data. Means for detecting an output shaft speed and generating corresponding sensor data, means for detecting a rotor shaft speed and generating corresponding sensor data
Data Source
Figure 1~2
Figure 3
AI summary
The invention relates to a drive device (1) for a bicycle (100), comprising: • a multi-gear transmission (2) and an output shaft (3), • a crankshaft (5) with a pedal crank (6) for transmitting drive power from a cyclist into the transmission (2), wherein the crankshaft (5) is operatively connected to the output shaft (3), • an electric machine (7) with a rotor shaft (8) for transmitting drive power from the electric machine (7) into the transmission (2), wherein the rotor shaft (8) is operatively connected to the output shaft (3), wherein the electric machine (7) is configured to at least reduce the cyclist's pedaling cadence, • means for detecting a pedal crank angle and a crankshaft speed and generating corresponding sensor data, • means for detecting an output shaft speed and generating corresponding sensor data.• Means for detecting a rotor shaft speed and generating corresponding sensor data, and • a control device (10) configured to process this sensor data and to control a downshift from a currently engaged gear to a lower gear based on this sensor data by energizing the electric machine (7). The invention further relates to a method for controlling the drive device (1), a control device (10), and a bicycle (100).