Hand-held Power Tool Speed Limitation Controller
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Solution Overview
Problem
Existing hand-held power tools with internal combustion engines face challenges in safely managing the start-up process, as the rotational speed can quickly exceed the clutch-in speed before the operator is ready, potentially leading to unintentional tool activation and safety risks.
Innovation Solution
A control system that includes a rotation speed sensor and a speed limitation controller, which calculates the integral of the rotational speed and deactivates the speed limitation after reaching an integration limit value, allowing the engine to operate above the clutch-in speed only when the operator is actively engaging the tool.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the throttle valve is positioned in a starting position to ensure efficient start-up, then the rotational speed of the combustion engine increases quickly above the clutch-in speed, but this presents a risk of unintentional working tool rotation and operator injury
Solution Approach 1:
The patent applies preliminary anti-action by implementing a start safety function that actively prevents the engine speed from reaching the clutch-in speed during start-up. The control system detects start-up conditions and limits the throttle opening or engine speed to keep the working tool stationary, counteracting the natural tendency of the engine to accelerate quickly when the throttle is opened for starting.
Solution Approach 2:
The control system performs preliminary action by detecting the start-up state and activating speed limitation before the engine reaches clutch-in speed. The system prepares the safety function in advance by monitoring engine speed and throttle position, and applies limiting action proactively to prevent unintentional activation before the operator is ready.
2Object-affected harmful factors
If a rotational speed limitation is initiated to prevent the combustion engine from reaching the clutch-in speed, then safety is improved, but the rotational speed limitation has to be deactivated to rev up the combustion engine above the clutch-in speed
Solution Approach 1:
The patent applies dynamics by making the start safety function dynamic rather than static. The control system continuously monitors engine speed, throttle position, and operating conditions to dynamically adjust the safety function's active state. The function is automatically activated when start-up conditions are detected and deactivated when normal operating conditions are detected, allowing the engine speed to freely exceed clutch-in speed during normal operation.
Solution Approach 2:
The control system uses feedback by continuously monitoring engine speed, throttle position, and other operating parameters to determine when to activate or deactivate the start safety function. The system receives feedback from sensors about the current operating state and adjusts the throttle control accordingly - limiting speed during start-up conditions while allowing full throttle control during normal operation.
3Object-affected harmful factors
If the start safety function remains active due to premature throttle opening, then safety is maintained, but the operator cannot increase the rotational speed above the clutch-in speed to operate the tool
Solution Approach 1:
The control system applies dynamics by continuously adapting the start safety function's state based on real-time monitoring of operating conditions. When the system detects that the engine is operating above idle speed for a predetermined period or that the throttle is held in a specific position range, it dynamically transitions from safety mode to operation mode, automatically deactivating the speed limitation to allow full throttle control and tool operation.
Data Source
Figure 1a~1b
Figure 1c~2a
Figure 2b
AI summary
Herein a hand-held power tool comprising an internal combustion engine (4) is disclosed. The hand-held power tool comprises, a working tool (6), a centrifugal clutch (8), and a control system (10). The internal combustion engine (4) has a clutch-in speed (ωC) above which the internal combustion engine (4) drives the working tool (6). A speed limitation controller (14), is configured to limit an engine speed at a limitation speed below the clutch-in speed (ωC). The control system (10) is configured to calculate an integral of the rotational speed of the internal combustion engine (4), and to deactivate the speed limitation controller (14) after the integral reaches an integration limit value, such that the internal combustion engine (4) is rotatable above the limitation speed (ωL) to drive the working tool (6) via the centrifugal clutch (8).