What is a Clutch?
A clutch is a mechanical device which is used to connect (or disconnect) two rotating shafts on the will of operator. One of the most prominent application of clutch is in modern automobiles.
Many times, it has been found that people confuse between Clutch, Coupling and Brakes. Let us understand differences between them with the help of their definitions.
Coupling: A coupling is a mechanical joint which is used to connect two rotating shafts together permanently. Operator can not engage or disengage the rotating shafts during operation.
You can read here a detailed article on coupling and its types.
Brakes: A brake is a joint between one stationary and one rotating part and the result of braking is stopping of the rotating part. A brake is always used to stop rotating parts.
Classification of Clutches
Clutches are classified into four types.
- Fluid Clutches
- Electromagnetic Clutches
- Friction Clutches
- Positive contact Clutches
Now we will explain each type of clutch in detail.
Positive engagement clutches
In these types of clutches engagement happens with the help of jaws or teeth. It means once engaged there is no chances of slip.
Advantages of positive engagement clutched
- No heat generation during operation
- No slip due to positive engagement
Disadvantages of positive engagement clutched
- Used when speed difference between the shafts is low
- They cannot be used at high speeds because it may result in a shock
In friction clutches engagement between the shaft happens due to friction between them. Single plate and multi plate, centrifugal clutches and cone clutches are the examples of friction clutches.
Image source: NPTEL
Advantages of friction clutch
- Its engagement is smooth
- No heat generation unless the operation requires frequent starts and stops
- Once engaged there is no slip
- In same cases it works as safety devices because it gets disengaged when torque crosses safety limit
Disadvantages of friction clutch
- Slip occurs at start and stop
- Due to slip wear and tear can happen
Desirable properties of friction material in friction clutches
- It should have high coefficient of friction
- Coefficient of friction should not vary with temperature
- It should have good thermal conductivity
- It should divide pressure equally in contacting surfaces
- To should have high resistance to wear
- It should remain unaffected by dirt and moisture
In these types of clutches power transmission achieved by means of electromagnetic field. Magnetic particle clutches, magnetic hysteresis clutches and eddy current clutches are the examples of electromagnetic clutches.
Advantages of electromagnetic clutches
- Their start and stop are smooth
- It has rapid response time
- It is easy to control
Disadvantages of electromagnetic clutches
- It has high initial cost
- Not suitable for high temperatures
- Risk of overheating during engagement
- Periodic check should be done for coil brushes
In these types of clutches power transmission happens by means of hydraulic pressure.
Advantages of fluid clutches
- It has extremely smooth starts and stops
- It has ability to absorb shocks
Disadvantages of fluid clutches
- There is always a slip
- Fluid used should be compatible with the clutch material