Cordless Power Tool Control Scheme for Battery Temperature Limits
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Solution Overview
Problem
Cordless power tools suffer from reduced power compared to corded counterparts and face issues with battery performance in cold temperatures, leading to potential damage or inefficiency due to high or low battery temperatures.
Innovation Solution
A control scheme is implemented in the power tool that regulates power supply to the motor based on battery temperature, using closed-loop and open-loop speed control modes, and adjusts ramp-up rates and PWM duty cycles to manage battery temperature and voltage thresholds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If cordless power tools use battery packs to provide convenience and portability, then ease of operation is improved, but power output decreases compared to corded tools
Solution Approach 1:
The patent implements dynamic control of the power tool operation based on real-time battery temperature monitoring. The system transitions between different operational modes (normal mode and cold mode) depending on temperature conditions, dynamically adjusting the duty cycle of the power switch circuit to optimize both power delivery and battery protection, thereby resolving the contradiction between maintaining power output and ensuring battery safety in cold environments
Solution Approach 2:
The patent changes the operational parameters of the power tool based on battery temperature. In cold mode, the system modifies the duty cycle parameter and ramp-up rate to prevent excessive current draw that would otherwise cause voltage sag and potential battery damage. This parameter adjustment allows the tool to maintain adequate power output while protecting the battery from cold-temperature stress
2Ease of operation
If the power tool operates in cold temperature conditions, then portability advantage is maintained, but battery voltage sags below nominal voltage due to increased impedance
Solution Approach 1:
The patent implements preliminary protective action by monitoring battery temperature before voltage sag occurs. When cold temperature is detected, the system proactively switches to cold mode operation, adjusting the duty cycle and ramp-up rate in advance to prevent excessive current draw and subsequent voltage sag, rather than reacting after voltage instability occurs
Solution Approach 2:
The patent employs feedback control by continuously monitoring battery temperature and using this information to adjust the power delivery parameters. The temperature signal feeds back to the controller, which modifies the duty cycle and ramp-up rate accordingly, creating a closed-loop system that maintains voltage stability in cold conditions
3Power
If the power tool uses high current draw to maintain power output, then power performance is improved, but battery temperature increases causing damage and fire hazard
Solution Approach 1:
The patent implements periodic duty cycle modulation through PWM (pulse-width modulation) control. Instead of continuous high current draw, the system uses periodic switching of the power switch circuit with variable duty cycles. This periodic action delivers average power while allowing thermal dissipation during off-periods, preventing excessive temperature rise while maintaining adequate power output
4Reliability
If the power tool implements temperature-based control modes, then battery protection is improved, but device complexity increases
Solution Approach 1:
The patent applies local quality by implementing temperature-specific control strategies in different operational regions. The controller detects battery temperature and applies appropriate control parameters (normal duty cycle vs. cold mode duty cycle with modified ramp-up rate) localized to the specific temperature condition, providing targeted protection without requiring complete system redesign
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
Enhances battery performance by preventing damage from extreme temperatures and maintaining efficient power delivery, ensuring safe and reliable operation across varying conditions.
Implementation Method 1
The controller is configured to set a pulse-width modulation (PWM) duty cycle associated with the power switch circuit based on the rotational speed of the motor in closed-loop speed control
Implementation Method 2
an electric motor disposed within the housing
Data Source
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AI summary
A power tool comprising: a housing; an electric motor disposed within the housing; a power terminal arranged to received electric power form a power supply; an actuator supported by the housing and engageable by a user to supply electric power from the power terminal to the electric motor; a power switch circuit disposed between the power terminal and the electric motor; a controller configured to control a switching operation of the power switch circuit to regulate power being supplied to the electric motor; a power contact switch coupled to the actuator and disposed on a first current path from the power terminal to the power switch circuit to selectively connect the power switch circuit to the power supply; a solid-state load switch disposed on a second current path from the power terminal to the controller, the solid-state load switch being controllable via at least one of an output of the power contact switch or a selfactivating feedback signal from the controller; and an override switch controllable via a self-deactivating signal from the controller and having an output commonly coupled to the output of the power contact switch to turn off the load switch even when the power contact switch is closed.