Brush Plate Convex Locking Segments for Electric Motor
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Solution Overview
Problem
Existing electric motor designs for hand-held power tools face issues with the secure axial locking of brush plates due to material stresses and deformation, especially under high temperatures, leading to unreliable locking over time.
Innovation Solution
A brush plate with uniformly distributed, convexly shaped locking segments that generate hydrostatic pressure without geometrical changes, providing stable contact forces within the reversibly elastic deformation region, and featuring a spherical shape for enhanced pressure distribution and two-point support during screwing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If concave hooks are used to lock the brush plate axially, then the brush plate can be secured in the housing, but tensioning and bending forces generate local stresses that lead to material retardation and loss of locking over time
Solution Approach 1:
The patent inverts the conventional concave hook design by using convex locking segments that project from the brush plate toward the housing. Instead of hooks engaging from behind, the convex segments make direct contact with the housing interior surface, reversing the engagement direction and eliminating the need for material deformation to achieve locking.
Solution Approach 2:
The locking segments are designed with a convex, rounded geometry that distributes contact forces more evenly across the housing surface. This curved configuration reduces stress concentration compared to sharp hooks, minimizing local stresses that cause material retardation and locking failure over time.
2Force
If high contact forces are generated in the locking elements, then stable locking is achieved, but plastic deformation and breakdown occur at high stresses
Solution Approach 1:
The convex, rounded geometry of the locking segments distributes contact forces over a larger area of the housing surface, reducing stress concentration. This allows high contact forces to be generated while keeping local stresses within the elastic deformation region, preventing plastic deformation and material breakdown.
Solution Approach 2:
The patent changes the geometric parameters of the locking elements from sharp hooks to convex segments with optimized curvature. This geometric modification alters the stress distribution pattern, enabling the generation of high stable contact forces while maintaining stresses below the plastic deformation threshold.
3Reliability
If the brush plate is secured with screws, then axial locking is achieved, but additional process steps and components are required
Solution Approach 1:
The patent merges the locking function into the brush plate itself by integrating convex locking segments directly onto the brush plate body. This eliminates the need for separate locking components such as screws or clips, reducing device complexity while maintaining reliable axial locking through the segments' direct engagement with the housing.
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 ensures long-lasting, reliable axial locking of the brush plate with increased contact forces and stability, even under high temperatures, without additional process steps or components, maintaining performance over time.
Implementation Method 1
In convexly shaped locking segments, the hydrostatic pressure, which is generated by locking forces, is produced without substantial geometrical changes. This can be probably attributed to the fact that with a uniaxial compression load, a compact convexly shaped body is geometrically similar to the formed deformation region, so that a uniaxial pressure load is converted, as a result of internal forces generated in the convexly shaped body, in a hydrostatic pressure acting in all directions.
Implementation Method 2
the locking segments have a spherical shape. Thereby, upon axial locking, primary acting point contact produces, as a result of the Hertzian pressure with the counter-contact surface of the stressed housing part, a large-surface pressure contact area already after a relatively short (in comparison with other contact surfaces) axial locking path
Implementation Method 3
A (all-sided) hydrostatic pressure (that is a pure third invariant of a stress tensor) is established, (with all materials) without change of the shape, in contrast to one-or two-sided compression stresses. This is possible because of absence of hydrostatic shear stresses which represent second invariant of the stress tensor. The one- or two-sided stresses lead, at high stresses, starting from plastic deformation to a breakdown. Thus, already in the reversibly elastic deformation region of the material of locking elements, relatively high (in comparison with other geometries) contact forces are produced that remain stable for a long time.
Data Source
AI summary
An electric motor fixedly axially securable in a housing includes a brush plate with a plurality of axially projecting, uniformly circumferentially distributed, convexly shaped, locking segments formed on the brush plate. The brush plate and the locking segments may be formed of an injection-moldable plastic material. The locking segments may be spherically shaped, and the there may be four locking segments. The brush plate may include a plurality of radial, circumferentially distributed, stop surfaces with which are associated a corresponding plurality of radially inwardly projecting radial guides in the housing.