Brushless Motor FET Heat Dissipation via Aluminum Housing
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Solution Overview
Problem
Brushless motors in electric grass cutters experience overheating of FETs due to increased motor load, leading to drive circuit burning and reduced motor power, particularly in work machines with varying load conditions.
Innovation Solution
The electric grass cutter design incorporates a brushless motor with a housing made of aluminum alloy serving as a heat sink for FETs, along with a control system that includes a voltage detecting circuit and current detecting circuit to manage FET operation, and a rotor with an annular magnet and fan for cooling, ensuring efficient heat dissipation and preventing overheating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If FETs are used as switching elements in the drive circuit to improve motor control efficiency, then motor power and efficiency are improved, but heat generation increases causing FET overheating and potential drive circuit burning
Solution Approach 1:
A heat sink is introduced as an intermediary component between the FET and the environment. The heat sink absorbs heat from the FET through thermal conduction and dissipates it to the surrounding air, serving as a mediator that protects the FET from overheating while allowing the FET to operate at high power levels.
Solution Approach 2:
The patent utilizes air flow (pneumatic principle) for cooling the FET. A fan generates air flow that passes over the heat sink, enhancing convective heat transfer from the heat sink surface to the air, thereby improving the dissipation of heat generated by the FET.
2Productivity
If motor load is increased to improve cutting performance, then productivity is improved, but FET heat generation increases leading to reduced motor power and reliability
Solution Approach 1:
The heat sink acts as a protective intermediary that decouples the FET from the thermal effects of high motor load. By providing a dedicated heat dissipation path, the heat sink allows the FET to withstand higher loads without compromising reliability, thus enabling improved cutting performance.
Solution Approach 2:
The cooling system operates autonomously to manage FET temperature during high-load operation. The fan continuously provides air flow to the heat sink, creating a self-regulating thermal management system that maintains FET reliability under varying load conditions without requiring external intervention.
3Temperature
If conventional cooling methods are used separately from the motor, then heat dissipation is achieved, but device complexity and space requirements increase
Solution Approach 1:
The cooling system is merged with the motor structure. The heat sink is integrated into the motor housing or directly coupled with the FET mounting area, and the fan is positioned to utilize the motor's existing air flow path. This integration combines the motor and cooling functions into a unified system, reducing overall complexity and space requirements compared to separate cooling systems.
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
This design effectively prevents drive circuit burning and maintains high motor efficiency by managing FET heat and load variations, ensuring reliable operation in varying conditions.
Implementation Method 1
the FET is fixed in contact with the housing or a heat sink provided at the housing
Implementation Method 2
The rotor is provided with a fan
Data Source
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AI summary
An electric grasscutter includes a motor (50) which drives a rotary blade (42). The motor (50) is a brushless motor accommodated in a motor housing (51) and including a rotor (53) provided integrally with an output shaft (52), and a stator (54) fixed to the motor housing (51). A motor control circuit which drives the motor (50) is accommodated in the motor housing (51). The motor control circuit includes an inverter having FETs (81-86) as switching elements, and a control section to control the FETs (81-86). The FETs (81-86) are fixed in contact with the motor housing (51).