Direct-Drive Lawn Mower Spindle Assembly With Slip Blade Coupling
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Solution Overview
Problem
The direct-drive electric motor in lawn mower spindle assemblies lacks a force transmission element to absorb impact forces, risking damage from blade impact events, and the lower spindle bearing wears out faster, requiring careful servicing to avoid damaging sensitive electrical components.
Innovation Solution
An electric motor design with a spindle housing, upper and lower bearings, a blade adapter, and a debris guard that includes a biasing mechanism to generate frictional coupling between the blade and spindle shaft, allowing the blade to slip during impact and limiting spindle shaft movement during bearing replacement, thus protecting the motor components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a direct-drive electric motor is used in the spindle assembly, then the motor can directly drive the blade without belts or transmission elements, but the motor becomes vulnerable to damage from blade impact forces and lower bearing wear
Solution Approach 1:
The patent applies beforehand cushioning by incorporating a belt-driven transmission system between the electric motor and blade, where the belt acts as a cushioning element that can absorb impact forces from blade strikes on objects. This allows the motor to be protected from direct impact loads while still achieving effective blade drive, resolving the contradiction between direct-drive efficiency and motor protection reliability
Solution Approach 2:
The patent uses an intermediary belt transmission system that mediates between the electric motor and blade. The belt serves as a protective intermediary that can slip or stretch during impact events, preventing direct transmission of harmful forces to the motor and bearing components while maintaining operational drive capability
2Ease of repair
If the lower bearing is serviced or replaced in traditional spindle assemblies, then the bearing can be maintained, but the spindle shaft may tilt or move from its operational position without damaging other components
Solution Approach 1:
The patent applies beforehand cushioning by designing the lower bearing support structure with compliance elements that accommodate bearing removal and installation without transmitting excessive forces to the spindle shaft. This cushioning effect prevents shaft misalignment during routine bearing maintenance while maintaining precise operational alignment
Solution Approach 2:
The patent implements dynamics by creating a lower bearing support structure that is dynamically compliant during maintenance operations but rigid during operation. The support structure allows for easy bearing removal and installation while automatically maintaining proper spindle shaft alignment when the bearing is installed, resolving the contradiction between ease of repair and alignment reliability
3Reliability
If a force transmission element like a belt is used to absorb impact forces, then the belt can protect components through elasticity or slipping, but the system lacks the direct coupling efficiency of a direct-drive system
Solution Approach 1:
The patent applies parameter changes by carefully selecting belt tension, material properties, and transmission ratios to optimize both impact absorption capability and power transmission efficiency. The belt system is parameterized to provide sufficient slip or stretch during impacts while maintaining high efficiency during normal operation, resolving the contradiction between reliability and productivity
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 effectively absorbs impact forces and facilitates safe servicing of the lower bearing without damaging the electric motor, reducing the risk of component damage and extending the spindle assembly's lifespan.
Implementation Method 1
a biasing member positioned in the gap and deflected by the blade mounting fastener when the gap is narrowed, wherein the biasing member generates a blade coupling force on the blade
Implementation Method 2
the blade coupling force generates a blade coupling friction between the blade and the bearing surface to frictionally couple the blade and the spindle shaft for rotation together
Data Source
AI summary
A configuration of a direct drive lawnmower spindle assembly to protect sensitive electric motor components is provided. A spindle shaft of the spindle assembly is supported by upper and lower bearings. An upper end of the spindle shaft is mounted to a rotor of the electric motor and a lower end of the spindle shaft extends through the clearance opening. The lower bearing is supported by a lower bearing carrier that is mounted to the bottom of the spindle housing. The lower bearing can be serviced by removing the lower bearing carrier. A clearance gap between the spindle shaft and the clearance opening is sufficiently small to limit spindle shaft tipping to a degree that will not damage the motor. The invention also provides a friction coupling system for coupling a blade with the rotating spindle shaft.