Bicycle Drive Unit Torque Combining Mechanism
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Solution Overview
Problem
Conventional coaster brakes cannot be effectively operated on electrically assisted bicycles due to the one-way clutch preventing rotation of the crank arm in response to the electric motor, resulting in the front gear not rotating when the crank arm is turned in a rearward direction.
Innovation Solution
A bicycle drive unit incorporating a crank axle, motor, output member, and torque combining mechanism with a one-way clutch that allows rotation of the output shaft to the output member only in the forward direction, enabling the coaster brake to function by separating the motor's rotation from the crank axle's rearward rotation, thus allowing the rearward rotation of the crank arm to directly engage the front sprocket.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a one-way clutch is disposed between the crank arm and front gear to prevent rotation in response to electric motor rotation, then the motor can assist pedaling without causing reverse rotation, but the front gear does not rotate when the crank arm is rotated in a rearward direction, making the coaster brake inoperable
Solution Approach 1:
The transmission system is segmented into two independent pathways: one for motor-to-gear transmission (controlled by first one-way clutch) and one for crank-to-gear transmission (controlled by second one-way clutch). This segmentation allows each pathway to operate independently, enabling the coaster brake to function while maintaining motor assistance capability.
Solution Approach 2:
A second one-way clutch is introduced as an intermediary component between the crank arm and front gear. This intermediary element mediates the interaction between the crank arm and gear, allowing rearward rotation of the crank arm to drive the front gear and operate the coaster brake, while preventing the motor from causing reverse gear rotation.
2Adaptability or versatility
If the crank arm is non-rotatably coupled to the front gear, then the coaster brake can be operated by rearward crank rotation, but the one-way clutch prevents the front gear from rotating when the crank arm rotates rearward
Solution Approach 1:
The coupling between the crank arm and front gear is made dynamic through the second one-way clutch, which selectively engages and disengages based on rotation direction. This dynamic coupling allows the system to adapt its behavior: enabling gear rotation during rearward crank rotation for brake operation, while preventing gear rotation during forward rotation when motor assistance is provided.
3Power
If the output member is fixed to the crank axle, then the motor rotation is directly transmitted to the crank arm, but the crank arm cannot rotate independently in the rearward direction to engage the coaster brake
Solution Approach 1:
The power transmission system is segmented so that the output member is not rigidly fixed to the crank axle but instead connected through a torque combining mechanism with one-way clutches. This segmentation allows the output member to transmit motor power forward while permitting the crank arm to rotate independently rearward for brake engagement.
Solution Approach 2:
The rotational coupling parameters between the output member and crank axle are changed from fixed to conditional through the use of one-way clutches. The coupling stiffness and rotational freedom are dynamically adjusted based on rotation direction, enabling both motor power transmission and independent crank rotation for braking.
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 the operation of the coaster brake on electrically assisted bicycles by ensuring the crank arm's rearward rotation is transmitted to the front sprocket, enhancing braking efficiency and functionality.
Implementation Method 1
The torque combining mechanism is configured to operatively separate the output shaft of the motor from the output member for preventing rotation of the crank axle from being transmitted to the output shaft of the motor as the crank axle rotates about the first rotational axis in a second rotational direction
Data Source
AI summary
A bicycle drive unit includes a crank axle, a motor, an output member and a torque combining mechanism. The crank axle is rotatable about a first rotational axis. The motor has an output shaft rotatable about a second rotational axis. The output member is rotatable about the first rotational axis in a first rotational direction as the crank axle rotates about the first rotational axis in the first rotational direction. The torque combining mechanism operatively couples the output shaft of the motor to the output member to transmit rotation of the output shaft of the motor to the output member. The torque combining mechanism operatively separates the output shaft of the motor from the output member for preventing rotation of the crank axle from being transmitted to the output shaft of the motor as the crank axle rotates about the first rotational axis in a second rotational direction.