Planetary Gear E-Bike Drive Stepless Ratio Control
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Solution Overview
Problem
Existing bicycle auxiliary drives face challenges in achieving a non-functionally continuously variable torque transmission from the crankshaft to the driven wheel with minimal additional gearing effort and a compact design, particularly in pedelecs and e-bikes, where the torque transmission varies with rotational movements around coaxial axes of the sun, planet carrier, and ring gear.
Innovation Solution
The solution involves varying the speed of the sun of the planetary gear through a variable braking torque, either mechanically, hydrodynamically, or electromechanically, allowing for stepless control of the transmission ratio, eliminating the need for a separate torque sensor and enabling the use of the generator current to measure the transmission ratio and instantaneous torque, while using a speed-controlled DC motor to intervene in the planetary gear for active speed adjustment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a planetary gear set is used with fixed gear ratios, then the structure is simple and reliable, but the torque transmission cannot be continuously varied
Solution Approach 1:
The patent applies the dynamics principle by making the previously stationary ring gear rotatable, transforming it from a fixed structure to a dynamic one. This enables continuous variation of the torque transmission ratio by controlling the rotational speed of the ring gear, while maintaining the simplicity of the planetary gear set structure without requiring complex additional gearing mechanisms.
Solution Approach 2:
The ring gear serves multiple functions: it acts as both a structural component of the planetary gear set and a controllable element for varying the torque transmission ratio. Additionally, a motor is integrated that can function both to drive the ring gear for ratio variation and to generate electrical energy during braking, demonstrating multi-functionality that reduces overall system complexity.
2Adaptability or versatility
If the ring gear is made rotatable for continuous ratio variation, then adaptability improves, but structural complexity increases
Solution Approach 1:
The motor integrated into the system serves dual purposes: it can drive the ring gear to achieve continuous torque transmission ratio variation, and it can function as a generator during braking to recover energy. This multi-functionality eliminates the need for separate mechanisms for ratio control and energy recovery, reducing overall structural complexity.
Solution Approach 2:
The patent merges the functions of the ring gear support structure and the motor mounting into a single integrated assembly. The motor is directly coupled to the ring gear, combining the drive mechanism and the ratio control mechanism into one unified structure, thereby minimizing additional gearing effort and structural complexity.
3Measurement precision
If a separate torque sensor is installed for electrical control, then measurement precision improves, but device complexity and cost increase
Solution Approach 1:
The system uses itself to measure torque by utilizing the electrical current generated by the motor when operating in generator mode during braking. This self-service approach eliminates the need for external torque sensors, as the generator current inherently provides information about the torque being transmitted, simplifying the device structure and reducing costs.
Solution Approach 2:
The patent changes the measurement parameter from mechanical torque sensing to electrical current measurement. By monitoring the electrical parameters (current, voltage, power) of the motor-generator, the system indirectly but accurately determines the torque transmission without requiring additional mechanical sensing components.
4Device complexity
If mechanical braking is used to control sun gear speed, then simplicity is maintained, but energy is lost as heat
Solution Approach 1:
The patent converts the previously harmful effect of energy dissipation during braking into a beneficial outcome by using the motor as a generator. The kinetic energy that would have been lost as heat in mechanical braking is instead converted into electrical energy that can be stored in the battery, transforming energy waste into energy recovery.
Solution Approach 2:
The patent replaces the mechanical braking system with an electromagnetic braking system. Instead of using friction-based mechanical brakes to slow the sun gear, the motor operates in generator mode, using electromagnetic induction to create a braking effect while simultaneously recovering energy, thereby eliminating the need for separate mechanical brake components.
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
This approach allows for a compact and efficient continuously variable torque transmission, optimizing the combination of pedal and support motor torques, reducing the complexity of gear switching, and enabling the reuse of braking energy to recharge the support motor, thus enhancing the overall efficiency and control of the bicycle auxiliary drive.
Implementation Method 1
The rotational movement around this third axis can be subjected to a variable braking torque. This can be achieved mechanically, through variable friction, for example on a shaft-mounted drum or disc; but also, for example, hydrodynamically or electromechanically. In the latter case, this shaft, which is not structurally fixed to rotation, drives, for example, a dynamo-electric generator.
Data Source
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AI summary
An electric auxiliary drive (11) for an electric bicycle avoids unpleasant gear ratio jumps due to switching between different gear pairs by implementing a continuously variable transmission of the torques transmitted from the pedal crankshaft (12) and the support motor (21) to the output gear (14) via a planetary gear set (15). The support motor (21) and the crankshaft (12) both drive the planet carrier (16), the latter via a freewheel (19), and the sun gear (23) drives the output hollow shaft (13). To vary the gear ratio, in addition to the two freely rotating shafts (28) of the three concentric axes of the planetary gear set (15), the rotation of the ring gear (24) about the third axis (28) is no longer fixed, but passively and variably braked or actively driven in a speed-controlled manner.