Permanent Magnet Wrap Spring Clutch Design
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Solution Overview
Problem
Wrap spring clutches require electrical power to transmit torque and may experience incomplete disengagement due to low momentum or high drag, leading to excessive wear and premature failure.
Innovation Solution
A wrap spring clutch design utilizing a permanent magnet to engage the spring without electrical power, combined with an electromagnet to ensure complete disengagement by redirecting the magnetic field, allowing the spring to return to its resting diameter and uncouple the input and output hubs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a standard logic wrap spring clutch uses an electromagnet to connect the free end of the spring to the drive shaft for torque transmission, then torque transmission is achieved, but electrical power is required which increases energy consumption
Solution Approach 1:
The patent replaces the electromagnet-based mechanical actuation system with a permanent magnet system. The permanent magnet creates a magnetic field that directly acts on the ferromagnetic control collar to engage the spring, eliminating the need for electrical power during torque transmission. The electromagnet is only used during disengagement, significantly reducing overall energy consumption.
Solution Approach 2:
The permanent magnet provides continuous magnetic force to maintain spring engagement without requiring external energy input. The system uses the inherent magnetic properties of the permanent magnet and ferromagnetic materials to sustain torque transmission capability without ongoing electrical power consumption.
2Use of energy by moving object
If a reverse logic wrap spring clutch relies on momentum of the driven shaft to unwrap the spring for disengagement, then electrical power is not needed for engagement, but incomplete disengagement occurs in low momentum or high drag applications leading to excessive wear
Solution Approach 1:
The patent replaces the momentum-dependent mechanical unwrapping mechanism with an electromagnet-based active disengagement system. The electromagnet, when energized, creates a magnetic field that pulls the control collar away from the drive shaft, actively unwrapping the spring regardless of the driven shaft's momentum or drag conditions, ensuring reliable complete disengagement.
Solution Approach 2:
The electromagnet serves as an intermediary device that provides the necessary force to overcome friction and drag during disengagement. By introducing this active magnetic force mediator, the system ensures the control collar can be reliably moved to the disengaged position even when the driven shaft lacks sufficient momentum.
3Ease of operation
If the spring inside diameter is made larger than the shaft diameter for easy disengagement, then the clutch can disconnect more easily, but torque transmission capability is reduced
Solution Approach 1:
The patent makes the spring inside diameter dynamic rather than fixed. When the control collar is in the engaged position, the spring is compressed to a smaller inside diameter that provides strong torque transmission. When disengaged, the spring returns to its larger natural inside diameter for easy disconnection. This dynamic adjustment of spring diameter resolves the contradiction between torque capability and disengagement ease.
Solution Approach 2:
The control collar performs a preliminary action of compressing the spring before torque transmission begins. This pre-compression reduces the spring's inside diameter to match the shaft diameter, ensuring optimal torque transmission capability is established in advance before the clutch operates under load.
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
Enables torque transmission without electrical power and ensures complete disengagement even in applications with low momentum or high drag, minimizing wear and power consumption.
Implementation Method 1
A permanent magnet is disposed proximate an input end of the control collar and provides a magnetic field which magnetically attracts the control collar
Implementation Method 2
the magnetic field generated by the permanent magnet tends to pass through the pole, control collar, end element, clutch housing and input flange, thereby attracting the moveable control element toward the permanent magnet
Implementation Method 3
a coil, disposed in a coil housing, that can be selectively supplied with an electrical current. When electrical current is caused to pass through the coil, it will generate a magnetic field that functions to redirect the magnet field generated by the permanent magnet
Data Source
AI summary
A permanent magnet activated wrap spring clutch (10). A coil spring (32) surrounds an input hub (14) and an output hub (22) and is selectively engaged to wrap down upon the hubs for the transmittal of torque. In an unpowered, engaged condition of the clutch, a permanent magnet (40) attracts a control collar (38) attached to the spring into frictional engagement with a rotating input element (20). Rotation of the control collar causes the spring to wrap down from its somewhat oversized diameter at rest to grip the hubs. In a powered, disengaged condition of the clutch, an energized coil (44) causes the magnetic field of the permanent magnet to move away from the control collar, thereby removing the frictional engagement and allowing the spring to unwrap. The clutch provides torque transmittal without electrical power and ensures complete disengagement regardless of a low momentum or high drag on the output.