Bicycle Transmission Switching Mechanism for High-Torque Ratio Changes
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Solution Overview
Problem
Bicycle transmission devices face performance degradation due to increased torque making it difficult to release the connection between the crankshaft and output part, leading to inefficient switching mechanisms.
Innovation Solution
A bicycle transmission device with a switching mechanism that includes a one-way clutch and a switching unit, allowing for two distinct rotational speed ratios by selectively switching between states, reducing the force required for coupling and decoupling, and utilizing an assist motor to reduce torque application.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the transmission mechanism decelerates the rotation of the crankshaft to increase output torque, then the torque of the output part becomes greater than the torque of the crankshaft, but it becomes more difficult for the switching mechanism to release the connection between the crankshaft and the output part as torque increases
Solution Approach 1:
The transmission device is divided into two independent transmission paths: a direct connection path (crankshaft directly to output part) and a deceleration path (crankshaft through transmission mechanism to output part). The switching mechanism selectively engages or disengages the deceleration path by controlling the connection between the transmission mechanism and the output part, allowing easy switching between high torque and low torque modes without the switching mechanism having to overcome high torque to disengage.
Solution Approach 2:
A switching mechanism acts as an intermediary between the crankshaft and the output part, controlling whether the transmission mechanism is connected to the output part. When the switching mechanism disconnects the transmission mechanism from the output part, the high torque is isolated from the switching mechanism, allowing it to easily release the connection. The switching mechanism thus mediates between the high torque deceleration path and the low torque direct path.
2Adaptability or versatility
If a switching mechanism is used to switch between direct connection and deceleration states, then two transmission ratios are obtained, but the transmission performance degrades when high torque is applied to the switching mechanism
Solution Approach 1:
The transmission system is segmented into two separate paths: a direct connection path that provides a 1:1 transmission ratio with no torque multiplication, and a deceleration path that provides reduced speed with increased torque. The switching mechanism only needs to control engagement/disengagement of the deceleration path, not manage torque transitions, which maintains reliability while providing adaptability.
Solution Approach 2:
Instead of having the switching mechanism directly manage torque transitions between different transmission ratios, the design inverts the approach by using a one-way clutch to automatically manage torque flow. The switching mechanism simply controls the connection state, while the one-way clutch handles the torque management, separating the switching function from the torque management function to improve reliability.
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
Improves transmission performance by simplifying the torque switching process and reducing the impact of assist motor torque, enhancing efficiency and ease of operation.
Implementation Method 1
The one-way clutch is configured to switch between a third state in which rotation is not transmitted from the first rotating body to the output part, and a fourth state in which rotation is transmitted from the first rotating body to the output unit.
Implementation Method 2
The switching unit includes a plurality of pawls that can be engaged with a plurality of gear teeth of the third rotating body, and an elastic member that elastically deforms in accordance with engagement and disengagement of the pawls with the gear teeth.
Data Source
AI summary
A bicycle transmission device basically includes an input rotational shaft, an output part, a transmission mechanism and a switching mechanism. The transmission mechanism includes a first rotating body configured to transmit rotation of the input rotational shaft and a fourth rotating body configured to transmit the rotation of the input rotational shaft. The switching mechanism is configured to selectively switch between a first state in which a ratio of a rotational speed of the output part to a rotational speed of the input rotational shaft is a first ratio and a second state in which the ratio is a second ratio that is different from the first ratio. The switching mechanism includes a one-way clutch and a switching unit.