KEVOS® MAKEOS · Power Transmission
Centrifugal Clutch Check (Engagement Speed, Torque at Running Speed, Idle Clearance)
For a centrifugal clutch with spring-held shoes, at what speed does it start to engage, how much torque does it carry at running speed, and will it stay free at idle?
Check of a shoe-type centrifugal clutch: the centrifugal force on each shoe at speed (as the centrifugal force tool), the speed at which it equals the spring force holding the shoe in (engagement speed), the net shoe force and the friction torque at the running speed from the number of shoes, friction coefficient and drum radius, against the torque needed with a service factor and the idle speed at which the clutch must stay disengaged.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Number of shoes | shoes | Number of friction shoes. |
| Mass of each shoe | kg | Mass of each shoe with its lining. |
| Radius to the shoe centre of gravity | mm | Radius from the clutch axis to each shoe’s centre of gravity when engaged. |
| Spring force holding each shoe in (at contact) | N | Inward force of the springs on each shoe when it just touches the drum. |
| Drum inside radius | mm | Inside radius of the drum where the linings rub. |
| Lining friction coefficient | Friction coefficient of the lining on the drum. | |
| Duty | ||
| Running speed | rpm | Speed the clutch runs at under load. |
| Idle speed (must not engage) | rpm | Engine idle speed, at which the clutch must not drag. |
| Torque needed at running speed | N·m | Torque the driven machine needs. |
| Service factor | Factor for starting and shock loads. | |
Method and formulas
- Centrifugal force F = m ω² r (as the centrifugal force tool).
- Engagement when m ω² r = spring force: ω = √(F_s ÷ (m r)).
- Torque = shoes × μ × (m ω² r − F_s) × drum radius.
- Example: engages at 1,232.8 rpm; carries 83.055 N·m at 3000 rpm.
Limitations
- Leading and trailing shoe effects (self-energising) are ignored; pivoted shoes can carry more torque one way.
- Linings worn so the shoes travel further change the spring force.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check a centrifugal clutch for an engine-driven machine
- Choose spring force for a set engagement speed
- See whether a clutch slips under load
Who it is for
- Design engineers
- Small engine mechanics
- Machine designers
What you get
- Centrifugal force per shoe
- Engagement speed
- Torque at running speed
Interpreting the result
- Clutch torque rises with the square of speed above engagement, so the clutch slips at low speed and grips firmly at full speed.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 187–190, 2433–2446. Topic reference; no source tables or recommended settings are reproduced.
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