Torque Overload Clutch for Compact Power Tool Transmission
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Solution Overview
Problem
Conventional hand-held motor driven power tools with torque overload clutches have limited torque range across different speed settings due to clutch placement after speed-change mechanisms, resulting in reduced torque availability at high speeds.
Innovation Solution
The clutch mechanism is rearranged to be placed closer to the motor, with a manually operable dial for torque adjustment, allowing the clutch spring to be housed within the motor and gearbox volume, enabling torque interruption at a predetermined threshold across all speed settings by varying the spring force applied to clutch plates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the clutch mechanism is arranged on the output gear of a reduction gear train, then the torque force required before clutch slip is relatively high, but this requires a relatively large and heavy spring to apply the necessary forces
Solution Approach 1:
The clutch mechanism is repositioned from the output gear (downstream) to an intermediate gear (upstream) in the transmission train. This spatial reconfiguration changes the torque multiplication relationship, allowing the same clutch mechanism to engage at lower spring forces while maintaining the required torque threshold at the output.
Solution Approach 2:
The clutch mechanism is designed to dynamically adapt to different operating conditions. By positioning it upstream in the transmission, the clutch can engage at variable torque thresholds depending on the gear ratio being used, allowing the same mechanism to function effectively across multiple speed settings without requiring excessive spring force.
2Weight of moving object
If the clutch is arranged on a gear closer to the motor drive, then the spring size and weight are reduced, but the torque clutch has a limited range over each speed setting
Solution Approach 1:
The clutch mechanism is designed to serve multiple functions across different operating conditions. By positioning it upstream in the transmission and designing it to engage at variable torque thresholds, the same clutch mechanism provides full torque range availability across both low and high speed settings, making it universally applicable to all gear ratios rather than being limited to a single speed range.
3Length of moving object
If the clutch mechanism is disposed in a volume defined by the motor, motor housing and gear train, then the power tool becomes more compact with reduced length
Solution Approach 1:
The clutch mechanism is nested within the existing volume defined by the motor and gear train components. Specifically, the clutch mechanism utilizes the space between the motor housing and gearbox, effectively nesting it within the existing structural envelope. This eliminates the need for additional external space and reduces the overall tool length without requiring a complete redesign of the clutch arrangement.
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 arrangement provides a compact, lightweight power tool with full torque range availability across both low and high speeds, reducing tool length and allowing space for ancillary devices like work-piece illuminators.
Implementation Method 1
a clutch spring arranged for applying a spring force to a first clutch plate disposed in the gear train or on the motor spindle
Data Source
AI summary
A power tool transmission is described in which an overload clutch mechanism is arranged to provide a relatively compact power tool. A torque adjustment dial is arranged between the visible portions of the motor housing and the gearbox, and the dial is coupled to a compression spring such that rotation of the dial cause the spring to be compressed or decompressed, thereby adjusting the torque at which the clutch overloads and ratchets. The compression spring is arranged at least partially between the motor and gearbox or gear train, in a space which conventional power tools do not utilized for this purpose. Thus, the dimensions of the power tool's transmission can be reduced with respect to conventional power tools. Furthermore, the space on the gearbox immediately behind a chuck can be used for another purpose other than accommodating the adjustment collar, as is the case with conventional power tools.