Two-Stage Belt Drive Braking for High-Inertia Hand Tools
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Solution Overview
Problem
Existing hand-held tools lack the ability to be braked independently of their speed, particularly at high speeds and when equipped with high-inertia components like cutting disks, requiring excessive forces to brake effectively.
Innovation Solution
A hand-held tool with a two-stage belt drive system where the braking device acts on the belt drive directly or indirectly via a clutch drum, utilizing deflection rollers to maintain belt tension and increase the angle of wrap, allowing for speed reduction and efficient braking torque transmission, regardless of tool speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-stage belt drive is used, then the device complexity is reduced, but the braking force required at high speeds becomes excessively high
Solution Approach 1:
The belt drive is divided into two stages: a first belt drive stage with a first driving pulley and first driven pulley, and a second belt drive stage with a second driving pulley and second driven pulley. This segmentation allows progressive speed reduction, where the first stage reduces speed from the engine to an intermediate level, and the second stage further reduces it to the tool operating speed. This multi-stage approach distributes the braking force requirements across different speed levels, reducing the peak braking force needed compared to a single-stage system.
Solution Approach 2:
The patent introduces a clutch drum as an intermediary element between the first driven pulley and the second driving pulley. The clutch drum serves as both the driven element of the first stage and the driving element of the second stage, facilitating smooth power transmission and speed reduction across the two stages. This intermediary component enables the system to manage high-speed inertial forces more effectively by providing a transition point in the power transmission chain.
2Force
If the tool speed is reduced through multi-stage belt drive, then the inertial forces are reduced enabling effective braking, but the device complexity increases
Solution Approach 1:
The patent merges the clutch drum with the belt drive system, combining the functions of power transmission and speed reduction into a unified structure. The clutch drum is integrated as both the driven pulley of the first stage and the driving pulley of the second stage, eliminating the need for separate clutch and belt drive components. This merging reduces overall device complexity while achieving the desired multi-stage speed reduction to manage inertial forces.
Solution Approach 2:
The clutch drum serves multiple functions: it acts as the driven element of the first belt stage, the driving element of the second belt stage, and provides the mounting surface for the braking device. This multi-functionality reduces the total number of components needed in the system, simplifying the overall structure while enabling effective speed reduction and braking control.
3Loss of time
If a braking device acts directly on the tool, then the braking response is immediate, but the forces required are excessively high at high speeds
Solution Approach 1:
The braking device is positioned to act on the first driving pulley, which rotates at the higher engine speed, rather than directly on the tool which rotates at the lower operating speed. By applying brakes earlier in the power transmission chain, the system can reduce the speed of the engine and subsequently reduce the tool speed through the belt drive stages. This preliminary braking action allows the belt drive to progressively reduce inertial forces before they reach the tool, enabling effective braking without requiring excessively high forces.
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
Enables the tool to be braked quickly and efficiently at any speed, reducing the forces required for braking and ensuring reliable transmission of braking torque, even at high speeds and with high-inertia components, through a compact and structurally simple design.
Implementation Method 1
the deflection roller advantageously increases the angle of wrap on at least one belt pulley over which the at least one drive belt is guided
Implementation Method 2
The first and the second drive stage each cause a reduction in speed. The speed of the driven pulley of each drive belt is therefore lower than the speed of the driving pulley of this drive belt
Implementation Method 3
During operation, the braking device is held in the released position by the flyweights of the centrifugal clutch
Data Source
Figure 1~3
Figure 4~5
Figure 6~7
AI summary
The invention relates to a hand-held implement having a drive motor (14) which drives a tool (4) in rotation by means of a belt drive (70). The belt drive (70) has at least one first, driving belt pulley (27) and at least one second, driven belt pulley (28). A second belt pulley (28) is non-rotatably connected to the tool (4). The rotational speed of the second belt pulley (28) in operation is less than the rotational speed of the first belt pulley (27). The implement has a braking device (25) which acts on the belt drive (70). At least one first drive belt (31) of a first drive stage and a second drive belt (32) of a second drive stage act between the first belt pulley (27) and the second belt pulley (28) for transmission of the driving torque. The first drive belt (31) and the second drive belt (32) each effect a reduction in the rotational speed. The belt drive (70) comprises at least one deflecting roller (35, 36) which bears against at least one drive belt (32). In this way braking of the tool (4) is made possible regardless of the rotational speed of the tool.