Power Tool Clutch Assembly With Lock-Ring-Free Torque Adjustment
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Solution Overview
Problem
Rotary power tools with clutch assemblies face challenges in compact design due to the addition of a lock ring, which is required to prevent clutch slipping, increasing the axial length of the tool.
Innovation Solution
A clutch assembly with a wave spring biasing member and a sleeve made of high-temperature engineering thermoplastic, allowing for adjustable torque limits without a separate lock ring, utilizing asymmetric threads and a plastic inner sleeve for enhanced strength and reduced length.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a lock ring is added to prevent clutch slipping, then reliability is improved, but the axial length of the tool increases
Solution Approach 1:
The patent combines the lock ring function with the existing clutch assembly structure by utilizing the inner sleeve and gear case threads. The asymmetric thread design allows the inner sleeve to lock the clutch elements axially when rotated, eliminating the need for a separate lock ring component while maintaining clutch slipping prevention
Solution Approach 2:
The inner sleeve serves multiple functions: it adjusts torque limits by varying biasing member preload, and it locks the clutch assembly by preventing axial displacement of rolling elements when rotated to the lockout position. This multi-functionality eliminates the need for separate lock ring and adjustment mechanism components
2Device complexity
If a sleeve with asymmetric threads is used to adjust torque limits, then device complexity is reduced, but manufacturing precision requirements increase
Solution Approach 1:
The patent employs asymmetric thread design where the inner thread on the sleeve has a different pitch width than the outer thread on the gear case. This asymmetry enables the sleeve to convert rotational motion into axial displacement for torque adjustment, while the precision is managed through controlled clearance between the asymmetric thread profiles
3Strength
If a high-temperature engineering thermoplastic is used for the sleeve, then strength is improved, but manufacturing cost increases
Solution Approach 1:
The patent specifies high-temperature engineering thermoplastic materials with glass transition temperatures of at least 70°C and specific mechanical property thresholds. These engineered plastics provide the necessary strength and temperature resistance while avoiding the need for metal sleeves, reducing manufacturing complexity and cost
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
The solution enables a compact power tool design with adjustable torque limits and high torque capacity, preventing clutch slipping without a separate lock ring, while maintaining reliability and cost-effectiveness.
Implementation Method 1
a biasing member configured to bias the plurality of rolling elements into engagement with the output of the drive mechanism, and the biasing member includes a wave spring
Implementation Method 2
The sleeve includes an inner thread defining a first pitch width, the gear case includes an outer thread defining a second pitch width and meshed with the inner thread such that rotation of the sleeve about the axis relative to the gear case causes the sleeve to move along the axis relative to the gear case, and the first pitch width is greater than the second pitch width
Data Source
AI summary
A power tool includes a housing, a drive mechanism supported within the housing, a spindle operatively coupled to an output of the drive mechanism such that torque from the drive mechanism rotates the spindle about an axis, and a clutch assembly configured to selectively limit torque transfer from the drive mechanism to the spindle. The clutch assembly includes a plurality of rolling elements, a biasing member configured to bias the plurality of rolling elements into engagement with the output of the drive mechanism, and a sleeve movable along the axis to adjust a torque limit of the clutch assembly by varying a preload of the biasing member. The sleeve is made of a high-temperature, engineering thermoplastic.