Bidirectional Torque Limiter With Intermediate Race Against 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 coil spring's wire having a smaller outer diameter than the groove portion, leading to potential vibrations of the hatchback when stopped at fully-opened or intermediate positions.
Innovation Solution
The introduction of an intermediate race that fixes the first and second hook portions of the coil springs to the intermediate and outer races respectively, eliminating rotational backlash by ensuring the first coil spring is incapable of rotating with respect to the intermediate race and the second coil spring with respect to the outer race, using press-fitted hook portions and groove portions with suitable diameters and lubrication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the first coil spring's wire outer diameter is made smaller than the groove portion circumferential width, then the coil spring can be easily mounted and engaged, but rotational backlash occurs between the auxiliary member and outer race
Solution Approach 1:
The patent introduces a second coil spring as an intermediary element between the first coil spring and the outer race. The second coil spring's hook portion fits into a groove formed on the outer race, while the first coil spring's hook portion fits into a groove on the auxiliary member. This intermediary structure eliminates the direct gap connection, preventing rotational backlash while maintaining ease of mounting through the same hook-groove engagement mechanism.
2Device complexity
If the first coil spring is engaged with the auxiliary member using a groove portion, then the engagement is simple and easy to manufacture, but a circumferential gap is created causing rotational backlash
Solution Approach 1:
The second coil spring serves as a mediator that connects the first coil spring to the outer race through additional groove engagements. The first coil spring engages with the auxiliary member via its hook portion in a groove, and the second coil spring engages with both the first coil spring and the outer race through similar hook-groove connections. This multi-stage engagement maintains structural simplicity while eliminating the circumferential gap that causes rotational backlash.
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 reduces unfavorable vibrations of the hatchback caused by external forces like wind, enhancing safety and service life by ensuring the hatchback remains stable at fully-opened or intermediate positions.
Implementation Method 1
In a case where a rotation torque about a central axis for rotating the auxiliary member in one direction with respect to the outer race is applied and when the rotation torque is larger than a first predetermined value, the auxiliary member rotates with respect to the inner race by overcoming the frictional force between the first coil spring and the inner race.
Implementation Method 2
a first coil spring and a second coil spring both of which are formed by winding wires and mounted on the inner race so as to be in contact with the inner peripheral surface and the outer peripheral surface, respectively
Data Source
AI summary
A bidirectional torque limiter 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.