Magnetic Viscous Torque Layout for High Shear in Compact Drives
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Solution Overview
Problem
Existing torque generating devices using magnetic viscous fluids face challenges in achieving large shear stress while maintaining miniaturization, as the magnetic field is primarily applied near the outer peripheral portion of the rotor, limiting braking force and shear stress generation.
Innovation Solution
A torque generating device design featuring a magnetic disk with a third yoke that extends beyond the magnetic disk's outer peripheral edge, allowing a wide range of magnetic flux to cross between the first and second yokes, generating resistance force without increasing device size, and incorporating a permanent magnet for initial magnetic field application and flux control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the magnetic field is applied only near the outer peripheral portion of the rotor, then the device size can be reduced, but the braking force and shear stress generation are insufficient
Solution Approach 1:
The patent extends the magnetic field application from a limited radial position to include the axial dimension by adding a third yoke that spans the axial direction. This allows magnetic flux to pass through a larger volume of magnetic viscous fluid without increasing the radial footprint, thereby generating sufficient braking force while maintaining compact device dimensions.
Solution Approach 2:
The magnetic circuit is divided into three separate yokes (first, second, and third yokes) that work together to create an extended magnetic path. The third yoke segments the magnetic flux path to allow it to traverse axially through the magnetic viscous fluid, increasing the effective area for shear stress generation without expanding the overall device volume.
2Area of stationary object
If the third yoke is positioned on the outer side of the magnetic disk, then magnetic flux can pass through a wide range, but the device complexity increases
Solution Approach 1:
The three yokes are designed to work as an integrated magnetic circuit system where the first, second, and third yokes are magnetically coupled. This merging of components allows the complex function of extended flux passage to be achieved through coordinated interaction of multiple simpler elements rather than a single complex structure.
Solution Approach 2:
The third yoke serves multiple functions: it provides a magnetic path for flux to pass through the magnetic viscous fluid, it structures the magnetic field distribution, and it maintains the geometric relationship between the magnetic disk and yokes. This multi-functionality reduces the need for additional components, thereby managing complexity while achieving large flux passage area.
3Stress or pressure
If magnetic flux crosses between the first and second yokes, then large shear stress can be generated, but the magnetic field distribution becomes non-uniform
Solution Approach 1:
The magnetic field distribution is optimized to have different characteristics in different regions: near the center where high shear stress is needed, the flux density is concentrated, while toward the edges the third yoke distributes the flux more uniformly. This local quality variation allows high shear stress generation in critical areas while maintaining overall field stability.
Solution Approach 2:
The magnetic viscous fluid acts as an intermediary that transmits the magnetic field effects from the yoke structure to the magnetic disk. Its presence in the gap between the yokes allows the magnetic flux to generate shear stress on the rotating disk while the fluid's properties help distribute and stabilize the magnetic field throughout the interaction region.
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 design enables the generation of large shear stress and resistance force while allowing for miniaturization, with the magnetic field applied uniformly across the magnetic disk, ensuring effective torque generation and preventing magnetic particle sedimentation.
Implementation Method 1
a coil disposed so as to overlap the magnetic disk when viewed in a direction along a direction in which the rotation axis extends, a third yoke of which at least a region proximity to the magnetic disk is located on an outer side of the magnetic disk and the coil and that makes up a magnetic path of a magnetic field that is generated by the coil
Implementation Method 2
a magnetic viscous fluid filled between the magnetic disk and each of the first yoke and the second yoke... a resistance force (torque) can be generated in a direction based on the direction of the magnetic flux
Data Source
Figure 1(A)~1(B)
Figure 2
Figure 3
AI summary
[Object] To provide a torque generating device that uses a magnetic viscous fluid and that is suitable for miniaturization and able to obtain large shear stress. [Solution] The torque generating device includes a magnetic disk configured to rotate around a rotation axis, a first yoke located on one side and a second yoke located on an other side across the magnetic disk, a coil disposed so as to overlap the magnetic disk when viewed along a direction in which the rotation axis extends, a third yoke of which at least a region proximity to the magnetic disk is located on an outer side of the magnetic disk and the coil and that makes up a magnetic path of a magnetic field that is generated by the coil in cooperation with the first yoke and the second yoke, and a magnetic viscous fluid filled between the magnetic disk and each of the first yoke and the second yoke. The third yoke has a magnetic gap between the third yoke and the first yoke. The magnetic gap is formed at a position on an outer side of an outer peripheral edge of the magnetic disk or a position that overlaps the outer peripheral edge of the magnetic disk when viewed in the direction along the direction in which the rotation axis extends.