Power Tool Engine Speed Limiting for Safe Clutch Engagement
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Solution Overview
Problem
Existing hand-held power tools with internal combustion engines face challenges in safely starting the engine without unintentionally engaging the centrifugal clutch, leading to potential operator injury, as the start safety function often delays deactivation and fails to recognize intentional operator actions.
Innovation Solution
A control system with a rotation speed sensor and speed limitation controller that deactivates the speed limitation upon sensing acceleration and deceleration above the limitation speed, allowing the engine to operate above the clutch-in speed when the operator is actively using the tool, thereby ensuring safe and efficient start-up.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the speed limitation controller is activated during starting procedure to prevent accidental engagement, then operator safety is improved, but the deactivation is delayed and fails to recognize intentional operator actions
Solution Approach 1:
The control system continuously monitors throttle position and engine speed, using this feedback to detect intentional operator actions. When the throttle is opened beyond a predetermined threshold position, the system receives feedback indicating the operator intends to use the tool, triggering deactivation of the speed limitation controller. This feedback mechanism resolves the contradiction by making the safety system responsive to genuine operator intent while maintaining protection during accidental startup.
2Productivity
If the throttle valve is positioned in starting position with more air flow, then engine start-up efficiency is improved, but the engine speed quickly rises above clutch-in speed before operator is ready
Solution Approach 1:
The speed limitation controller is activated in advance during the starting procedure, before the operator releases the throttle. This preliminary action prevents the engine speed from reaching the clutch-in speed even when the throttle is in the starting position with high air flow. The limitation remains in place until the operator intentionally opens the throttle beyond the threshold position, at which point the limitation is deactivated. This resolves the contradiction by providing immediate protection during startup while allowing efficient operation once intended use begins.
3Reliability
If the start safety function remains active during idle to wide open throttle transitions, then safety is maintained, but the rotational speed cannot reach above clutch-in speed for normal operation
Solution Approach 1:
The speed limitation controller dynamically adjusts its operation based on real-time throttle position and engine speed conditions. During normal idle operation, the limitation keeps engine speed below clutch-in speed for safety. However, when the operator intentionally opens the throttle beyond the predetermined threshold position, the system detects this dynamic change and deactivates the speed limitation, allowing the engine speed to rise above clutch-in speed for normal operation. This dynamic behavior resolves the contradiction by adapting the safety function to the operator's actual intent rather than maintaining a static limitation.
Data Source
AI summary
A hand-held power tool comprising an internal combustion engine (4), a working tool (6), a centrifugal clutch (8), and a control system (10) is disclosed. The engine (4) has a clutch-in speed, above which the engine (4) drives the working tool (6). The control system (10) comprises a rotation speed sensor (12), and a speed limitation controller (14), which is configured to limit an engine speed at a limitation speed below the clutch-in speed. It is active or activated during a starting procedure of the internal combustion engine (4). The control system (10) is configured to deactivate the speed limitation controller (14) upon sensing at least one acceleration at a level above the limitation speed and sensing at least one deceleration at a level above the limitation speed, such that the engine (4) is rotatable above the limitation speed to drive the working tool (6).