Torque Limiter Ball Dynamics for Power Tool Durability
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Solution Overview
Problem
Existing torque limiters in power tools suffer from durability issues due to constant biasing force causing point contact and local wear between the ball, driving gear, and driven flange, leading to reduced tool lifespan.
Innovation Solution
A torque limiter design featuring a first and second rotating member, a ball, a pressing member, and an elastic member, with grooved regions allowing for line contact and reduced load on the ball, enabling torque transmission below a set value and interrupting it above, while the ball moves axially against the elastic member's biasing force, reducing wear through changed contact areas and rolling motion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the elastic member constantly applies biasing force to the ball via the pressing plate, then the torque limiter can reliably interrupt torque transmission when torque exceeds the set value, but the ball is prevented from rolling and comes in point contact with the driving gear, driven flange and pressing plate, causing local wear and reduced durability
Solution Approach 1:
The pressing member is designed to move dynamically between two states: applying biasing force to the ball when torque exceeds the set value (interrupting transmission), and releasing the ball to allow free rolling when torque is below the set value (enabling rolling contact). This dynamic adjustment resolves the contradiction by making the biasing force conditional rather than constant, allowing the ball to roll during normal operation while maintaining reliable torque interruption when needed.
2Power
If the ball is held in a radial holding groove and engages with a cam of the driving gear, then torque can be transmitted from the driving gear to the driven flange, but the constant biasing force prevents rolling motion and causes point contact, leading to local wear
Solution Approach 1:
The system dynamically switches between two operational modes: In the first mode, the pressing member releases the ball to allow free rolling contact with the driving gear cam, enabling torque transmission while reducing wear through rolling motion. In the second mode, the pressing member applies biasing force to interrupt torque transmission when the set torque limit is exceeded. This dynamic control enables both effective torque transmission and extended component life.
Solution Approach 2:
The biasing force parameter applied to the ball is changed based on torque conditions: when torque is below the set value, the biasing force is released allowing rolling contact; when torque exceeds the set value, the biasing force is applied to interrupt transmission. This parameter change resolves the contradiction by optimizing the ball's contact state according to operational conditions.
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
Enhances the durability of power tools by reducing wear on the ball and driven components through line contact and rolling motion, maintaining effective torque transmission while preventing excessive torque from causing damage.
Implementation Method 1
The elastic member applies a biasing force in the axial direction of the first rotating member with respect to the ball via the pressing member
Implementation Method 2
The ball serves to transmit torque between the first and second rotating members by engagement with the second rotating member in the circumferential direction
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
It is an object of the invention to provide an effective technique for improving the durability of a torque limiter utilized in a power tool. The object is achieved by a representative power tool (101) comprising a tool bit (119), a driving mechanism and a torque limiter (151). The torque limiter (151) includes first and second rotating members, a ball (155), a pressing member and an elastic member (159). The second rotating member includes a power transmitting region with a groove continuously formed from a deepest groove part to a shallowest groove part to allow torque transmission and a power transmission interrupted region with a groove shallower than the shallowest groove part of the power transmitting region to interrupts the torque transmission. According to this construction, when the ball (155) is in the power transmitting region, the pressing member contacts the first rotating member and is held in a position in which the biasing force of the elastic member (159) is prevented from acting upon the ball.