E-Bike Assist Control Using Crank Angle and Motor Current
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Solution Overview
Problem
Conventional electric power assisted bicycles require complex structures and modifications to detect pedal force, making it difficult to retrofit existing bicycles with electric power assist units without complicating the detection process.
Innovation Solution
A bicycle electric power assist device that uses a combination of rotation angle sensors, pedal force presence/absence determination units, gyro sensors, and voltage sensors to accurately estimate pedal force and pedaling state without modifying the bicycle, allowing for assist control based on these parameters while preventing ineffectual assist and excessive battery discharge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional pedal force detection methods are used, then pedal force can be detected, but the structure becomes complicated and requires bicycle modification
Solution Approach 1:
The patent replaces mechanical detection systems (strain gauges, force sensors) with an electromagnetic sensing approach. The rotation angle sensor detects crankshaft position, and the control unit calculates pedal force by analyzing current variations in the electric motor during different crank rotation phases, eliminating the need for mechanical force sensors and their complex installation on the bicycle
Solution Approach 2:
The patent introduces the electric motor as an intermediary element for indirect measurement. Instead of directly measuring pedal force, the system measures the current consumed by the electric motor at different crank angles, which indirectly reflects the pedal force applied by the rider through the motor's electromagnetic response
2Measurement precision
If conventional pedal force detection methods are used, then pedal force can be detected, but modification of the bicycle is required
Solution Approach 1:
The patent makes the electric motor serve multiple functions: it provides power assist to the rider while simultaneously acting as a sensor for detecting pedal force through current analysis. This multi-functionality eliminates the need for separate detection components and simplifies the retrofitting process, as the same motor component performs both propulsion and measurement functions
Solution Approach 2:
The system uses the electric motor's own operational characteristics (current consumption patterns during rotation) to detect pedal force. The motor essentially measures its own performance parameters to infer the rider's input force, eliminating the need for external detection devices that would require additional installation and modification work
3Ease of operation
If electric motor provides assist continuously, then rider receives constant assistance, but battery discharges excessively
Solution Approach 1:
The patent implements periodic assist control by analyzing the rotational speed variations of the crankshaft over time. The control unit provides motor assistance only during specific phases of the pedaling cycle when the crankshaft rotation speed decreases (indicating rider fatigue or resistance), and reduces or stops assist when rotation speed is stable or increasing, creating a rhythmic on-off assist pattern that conserves battery energy
Solution Approach 2:
The patent employs dynamic assist control where the motor output is continuously adjusted based on real-time detection of crankshaft rotation speed and its rate of change. The system transitions smoothly between different assist levels rather than maintaining a constant output, adapting the motor torque to match the rider's instantaneous needs and optimizing energy consumption by providing assistance only when and where it is most beneficial
4Measurement precision
If rotation angle sensor is used to detect crank position, then pedal force estimation is possible, but detection structure becomes more complex
Solution Approach 1:
The patent combines the rotation angle sensor function with the existing electric motor control system. The same sensor that detects crankshaft position for motor control purposes also provides data for pedal force estimation, merging two measurement functions into a single sensing component and reducing overall system complexity
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
Enables accurate assist control according to pedal force and pedaling state without complicating the detection structure or requiring bicycle modifications, ensuring effective assistance and extended battery life.
Implementation Method 1
a rotation angle sensor configured to detect a rotation angle of the crankshaft
Implementation Method 2
a gyro sensor configured to detect a tilt of the bicycle
Data Source
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AI summary
To allow assist control according to the pedal force to be performed in a bicycle electric power assist device without complicating the structure for detecting the pedal force and/or requiring modification of the bicycle, a bicycle electric power assist device (50) includes: an electric motor (54) connected in a torque transmitting relationship to a crank arm (26) or a crankshaft (24) driven by a pedal force from pedals (30) via the crank arm (28); a battery (102) to be mounted on a bicycle to serve as a power supply for the electric motor (54); a control unit (100) configured to control operation of the electric motor (54); a rotation angle sensor (110) configured to detect a crank rotation angle position of the crankshaft (24); and a current sensor (116) configured to detect a motor current of the electric motor (54), wherein the control unit (100) includes: a pedal force estimation/calculation unit (120) configured to estimate the pedal force of the pedals (30) from a difference between the motor current in a first crank rotation angle position and the motor current in a second crank rotation angle position which is different from the first crank rotation angle position; and a motor drive control unit (126) configured to control a drive current of the electric motor (54) according to the pedal force estimated by the pedal force estimation/calculation unit (120).