Short Answer:
An isochronous governor is a type of governor in which the equilibrium speed remains constant for all positions of the governor balls. In this type, there is no range of speed between the minimum and maximum limits, meaning the governor maintains the same speed regardless of load changes. The isochronous governor provides very high sensitivity and keeps the engine speed perfectly constant.
It is generally used in engines that require uniform speed, such as generators and turbines. However, due to its extreme sensitivity, it is rarely used in practical applications without damping mechanisms.
Detailed Explanation :
Isochronous Governor
An isochronous governor is a special type of centrifugal governor designed to maintain a constant engine speed, regardless of load variations. The term isochronous means equal time or constant speed. In this governor, the equilibrium speed remains the same for all radii of rotation of the governor balls, which means the governor operates at a single speed for all positions of the sleeve.
In a normal centrifugal governor, there is a certain speed range called the “range of speed” between the minimum and maximum equilibrium speeds. But in an isochronous governor, this range of speed is zero. Therefore, it provides an extremely quick response to any change in engine load. It is ideal for applications requiring a very steady speed, such as electric generators or precision engines.
Construction of Isochronous Governor
An isochronous governor can be constructed using a spring-loaded mechanism, similar to a Hartnell governor, but with carefully adjusted parameters to achieve zero speed range. The main components include:
- Spindle:
A vertical rotating shaft connected to the engine crankshaft. It transmits rotational motion to the governor mechanism. - Balls (Fly Balls):
Two or more balls mounted on arms rotate around the spindle due to centrifugal force. - Arms and Links:
The arms connect the balls to the sleeve. They convert the radial motion of the balls into vertical movement of the sleeve. - Sleeve:
The sleeve is mounted on the spindle and can move up or down. Its movement is linked to the throttle valve, which controls the fuel supply to the engine. - Spring (in Spring-Loaded Type):
A helical compression spring provides the controlling force that balances the centrifugal force of the balls. - Throttle Valve Mechanism:
It regulates the fuel or working fluid supply according to the sleeve movement to control engine speed.
Working of Isochronous Governor
The working principle of an isochronous governor is based on balancing the centrifugal force of the rotating balls with the controlling force provided by a spring or weights.
- At Normal Speed:
The centrifugal force on the balls equals the controlling force (spring tension or dead weight). The sleeve remains at a fixed position, and the fuel supply is constant. The engine runs at its designed constant speed. - When Speed Increases (No Range of Speed):
In a typical governor, an increase in speed causes the balls to move outward and the sleeve to rise. However, in an isochronous governor, the spring and linkage are designed so that the equilibrium speed does not change with ball movement. Thus, any small speed change immediately corrects itself — the system returns to the same speed instantly. - When Load Increases (Speed Falls):
Similarly, if the engine speed decreases, the spring immediately adjusts the sleeve position, increasing the fuel supply to restore the same speed.
This balance between the centrifugal and spring forces is maintained for all positions, ensuring that the speed remains truly constant.
Characteristics of Isochronous Governor
- Zero Range of Speed:
The difference between the minimum and maximum equilibrium speeds is zero. - Perfect Sensitivity:
The governor is infinitely sensitive, meaning even a very small change in speed causes a corrective action. - Stable Speed Control:
The speed of the engine remains absolutely constant, regardless of load fluctuations. - Fast Response:
The governor reacts immediately to any change in engine speed. - Unstable in Practice:
Due to very high sensitivity, it can cause continuous oscillations in engine speed if not damped properly.
Advantages of Isochronous Governor
- Maintains a perfectly constant speed.
- Provides quick corrective action.
- Suitable for machines requiring precise and uniform speed, such as electric generators.
- Reduces fuel fluctuations during load variations.
- Useful for high-performance engines and turbines.
Disadvantages of Isochronous Governor
- Extremely sensitive and may cause hunting (continuous speed oscillation).
- Difficult to achieve practically without damping.
- Requires precise adjustment and balancing of spring tension.
- Not suitable for heavy-load variations.
- Complex design compared to ordinary centrifugal governors.
Applications of Isochronous Governor
- Steam and gas turbines
- High-speed engines
- Electric power generators
- Aircraft engines
- Precision laboratory machines
In these applications, maintaining a constant speed is critical for performance and safety.
Difference between Isochronous and Ordinary Governor
| Feature | Isochronous Governor | Ordinary Governor |
| Range of speed | Zero | Has a range of speed |
| Sensitivity | Infinite | Finite |
| Stability | May become unstable | Generally stable |
| Speed control | Constant | Varies with load |
| Practical use | Limited | Widely used |
Conclusion
An isochronous governor is a highly sensitive type of centrifugal governor that keeps the engine speed constant for all positions of the governor balls. It eliminates the range of speed, making the engine run steadily under varying loads. Though its accuracy and response are excellent, its high sensitivity can lead to instability. Therefore, damping mechanisms are often used to make it suitable for practical applications such as turbines and generators, where constant speed is essential.