Drive Unit Transmission for Continuous Shifting Without Direction Inversion
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Solution Overview
Problem
Existing assist bicycle transmission systems face challenges in smoothly performing continuous shift changing operations, leading to interruptions in pedaling assist due to rotational direction inversion during shift changes.
Innovation Solution
A drive unit with a transmission system that includes a main shaft and a counter shaft, where the transmission selects a torque delivery gear without inverting the rotational direction, and incorporates one-way clutches to prevent torque delivery and reduce friction losses, allowing for continuous shift changing without interrupting pedaling assist.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If shift changing is performed by switching rotation of the assist motor from forward to backward rotation, then the deceleration ratio can be changed, but the continuous shift changing operation cannot be performed smoothly
Solution Approach 1:
Instead of changing shift by inverting the rotation direction of the assist motor, the patent uses a transmission mechanism that changes the gear ratio while maintaining the same rotation direction. The transmission includes a drive gear connected to the assist motor and a driven gear connected to the pedal crankshaft, with intermediate gears that allow ratio changes without direction reversal.
Solution Approach 2:
The patent introduces intermediate gears and a transmission mechanism as mediators between the assist motor and the pedal crankshaft. This transmission system enables smooth ratio changes by providing intermediate steps in the gear train, eliminating the need for direct motor rotation reversal.
2Adaptability or versatility
If the assist motor rotates backward to change shift, then the deceleration ratio is adjusted, but the pedaling assist is interrupted
Solution Approach 1:
The transmission mechanism is designed to maintain continuous rotation in the same direction while changing gear ratios. The drive gear continuously rotates in one direction, and the transmission system provides continuous torque delivery to the pedal crankshaft, ensuring uninterrupted pedaling assist during shift changes.
3Loss of energy
If one-way clutch is provided to block pedal torque delivery to electric motor, then torque loss due to friction is reduced, but the device complexity increases
Solution Approach 1:
The one-way clutch automatically blocks pedal torque delivery to the electric motor when the pedal rotation speed exceeds the motor rotation speed, without requiring external control or complex mechanisms. The clutch engages and disengages based on the relative rotation speeds, providing self-regulating torque management that reduces friction losses.
Data Source
AI summary
A drive unit includes: a pedal crankshaft to which a pedal stepping force of a rider is applied; an electric motor that detects a torque input to the pedal crankshaft and generates a drive force; and a transmission that changes shift of the drive force of the electric motor and delivers the drive force to the pedal crankshaft, the transmission includes a main shaft that supports a plurality of drive gears and a counter shaft that supports a plurality of driven gears that engage with the plurality of respective drive gears, and the transmission selects one torque delivery gear among the plurality of drive gears, delivers the drive force of the electric motor to the counter shaft, and shifts the torque delivery gear without inverting a rotational direction of the drive gear.