Bidirectional Torque Limiter Structure to Eliminate Rotational Backlash
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Solution Overview
Problem
The bidirectional torque limiter disclosed in Patent Document 2 experiences rotational backlash between the auxiliary member and the outer race due to a circumferential gap caused by the first hook portion being inserted into a groove portion, leading to potential vibration of the hatchback when stopped at fully-opened or intermediate positions, which is unfavorable for safety and service life.
Innovation Solution
The introduction of an intermediate race that fixes the first hook portion of the first coil spring and the second hook portion of the second coil spring, eliminating rotational backlash by ensuring the first coil spring is incapable of rotating with respect to the intermediate race and the second coil spring is incapable of rotating with respect to the outer race, using press-fitted hook portions and groove portions with suitable dimensions and orientations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the first hook portion is inserted into the first groove portion to engage the first coil spring with the auxiliary member, then the first coil spring is engaged non-rotatably with respect to the auxiliary member, but there is a circumferential gap between the first coil spring and the auxiliary member causing rotational backlash
Solution Approach 1:
The patent introduces a second coil spring as an intermediary element between the auxiliary member and the outer race. This second coil spring transmits rotational force in the opposite direction to loosen the first coil spring, thereby eliminating the need for a circumferential gap and preventing rotational backlash while maintaining engagement stability.
Solution Approach 2:
The patent changes the mechanical parameters by introducing bidirectional torque limitation with different predetermined values (first predetermined value and second predetermined value) for opposite rotation directions. This allows precise control of the clamping force and eliminates backlash by ensuring continuous contact between components through optimized spring preloading.
2Ease of manufacture
If the wire composing the first coil spring has an outer diameter smaller than the circumferential width of the first groove portion, then the first coil spring can be inserted into the groove portion, but this creates a circumferential gap leading to rotational backlash
Solution Approach 1:
The second coil spring acts as a mediator that transmits rotational force to loosen the first coil spring in the opposite direction. This intermediary mechanism allows the first coil spring to be easily assembled with a smaller wire diameter while preventing rotational backlash through the opposing loosening action, thereby maintaining both assembly ease and positional accuracy.
Solution Approach 2:
Instead of trying to eliminate the circumferential gap by increasing the wire diameter (which would make assembly difficult), the patent inverts the approach by using the second coil spring to actively loosen the first coil spring in the opposite direction. This inversion transforms the potential harmful gap into a controllable feature that does not cause rotational backlash.
3Extent of automation
If the bidirectional torque limiter is used to hold the hatchback at any angular position, then the hatchback can be held without electric means, but rotational backlash causes vibration when the hatchback is stopped
Solution Approach 1:
The second coil spring serves as an intermediary that actively counteracts rotational backlash by transmitting rotational force in the opposite direction. This eliminates vibration when the hatchback is stopped at any angular position while maintaining the electric-free holding capability, as the mechanical interaction between the two coil springs prevents play without requiring electronic intervention.
Solution Approach 2:
The patent optimizes the torque parameters by setting different predetermined values for bidirectional torque limitation. By carefully adjusting these parameters and the preloading force of the second coil spring, the system eliminates rotational backlash and resulting vibration while maintaining simple mechanical operation without electric means.
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 configuration effectively prevents rotational backlash, reducing unfavorable vibrations of the hatchback caused by external forces like wind when stopped at fully-opened or intermediate positions, enhancing safety and service life by maintaining stable angular position holding.
Implementation Method 1
the frictional force between the first coil spring and the inner race, and the frictional force between the second coil spring and the intermediate race
Implementation Method 2
a first coil spring formed by winding a wire and mounted on the inner race so as to be in contact with the outer peripheral surface; a second coil spring formed by winding a wire and mounted on the intermediate race so as to be in contact with the outer peripheral surface
Data Source
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AI summary
Provided is a novel bidirectional torque limiter free from any rotational backlash between an inner race and an outer race. A first hook portion (16) of a first coil spring (6) and a second hook portion (20) of a second coil spring (10) are to be fixed by an intermediate race (8) and an outer race (12), respectively.