Brushless Motor Drive Circuit Cooling in Power Tool Grip
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Solution Overview
Problem
The arrangement of switching elements on the rear surface of the circuit board in brushless DC motor-based electric power tools requires significant space, leading to increased length in the front-rear direction of the housing, and existing cooling methods are inadequate for large electric current flows, especially when the circuit board is positioned apart from the motor.
Innovation Solution
The electric power tool incorporates a brushless DC motor with the drive circuit and switching elements mounted on a board in the grip or handle portion of the housing, with an electric fan provided to cool the switching elements, and includes a temperature sensor for controlled fan operation, air intake and outlet on the side surfaces, and a detachable battery to optimize cooling and compact design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If switching elements are mounted on the rear surface of the circuit board with height direction parallel to the motor rotational shaft, then cooling performance is improved, but the length in the front-rear direction of the housing increases
Solution Approach 1:
The circuit board is rotated 90 degrees so that its surface extends in the radial direction of the motor rather than the axial direction. This dimensional reorientation allows switching elements to be mounted on the rear surface with their height direction parallel to the rotational shaft, achieving effective cooling through the motor's air flow path while preventing the housing length from increasing due to axial extension.
2Length of moving object
If the circuit board is provided in another position apart from the motor to reduce housing length, then the front-rear length of the housing is reduced, but effective cooling of the switching element becomes difficult
Solution Approach 1:
The circuit board is positioned in the radial direction of the motor rather than extending axially, allowing the switching element to be located close to the motor for effective cooling while maintaining a compact housing length. The board's surface extends radially to provide mounting space without increasing the front-rear dimension.
Solution Approach 2:
The housing is divided into distinct functional zones: the motor occupies the central axial space, the circuit board is positioned in the radial direction, and cooling air flow paths are segmented to direct air from the motor's front surface through the switching element to the rear surface, enabling independent optimization of each component's position.
3Temperature
If switching elements are cooled by a cooling fan rotated by the motor, then cooling is achieved, but the motor rotation state must be maintained for cooling to function
Solution Approach 1:
The switching element utilizes the motor's own rotational motion and air flow as a self-contained cooling mechanism. The motor's rotation naturally generates air flow that passes through the switching element mounted on the circuit board, eliminating the need for a separate cooling fan and ensuring cooling functionality is inherently tied to motor operation without requiring additional components.
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 configuration allows for effective cooling of the switching elements, reduces the front-rear length of the housing, and ensures reliable operation by maintaining efficient cooling regardless of motor rotation state, while preventing dust and heat from entering the housing.
Implementation Method 1
an electric fan is provided in the vicinity of the switching element in order to cool the switching element. There are provided below the grip portion of the housing an air intake for sucking the external air by the electric fan, and an air outlet for exhausting the air blown in the switching element
Implementation Method 2
since the large electric current flows in the switching element, it is necessary to cool the switching element
Data Source
AI summary
According to an aspect of the invention, an electric power tool which includes a brushless direct-current motor and a drive circuit that supplies drive power to the motor, and which rotates or drives a tool, characterized in that the drive circuit includes plural switching elements, and is arranged on a board provided in a grip portion of a housing or below the grip portion; and an electric fan is provided in the vicinity of the switching element for cooling the switching element.