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; instead, the governor maintains the same speed for all loads.

It is designed so that the controlling force is exactly proportional to the square of the speed, resulting in no variation in speed under steady-state conditions. Isochronous governors are ideal for maintaining a constant engine speed but can sometimes cause instability or hunting if not properly damped.

Detailed Explanation :

Isochronous Governor

An isochronous governor is a special type of centrifugal governor designed to maintain a constant mean speed of an engine, regardless of load variations. The word isochronous means “equal time” or “constant speed.” In this governor, the equilibrium speed of rotation remains the same for all positions of the governor balls. This means that when the load on the engine changes, the governor immediately corrects the fuel supply so that the engine speed remains constant without any delay or difference between minimum and maximum speeds.

In a normal governor, there exists a range of speed known as the governor effort range, which is the difference between the maximum and minimum equilibrium speeds for different positions of the balls. But in an isochronous governor, this range is zero. The entire operation takes place at one uniform speed. This feature makes it highly useful where precise speed control is essential, such as in power generation or high-speed engines.

Principle of Isochronous Governor

The working of an isochronous governor is based on the principle that the controlling force acting on the rotating balls must be directly proportional to the square of the angular speed of rotation. When this condition is perfectly maintained, the governor becomes isochronous.

When the engine load decreases, the speed of the engine tends to increase. The governor balls move outward due to the increased centrifugal force. This movement adjusts the throttle valve to reduce the fuel supply, thereby bringing the engine speed back to its normal value. Similarly, when the load increases, the engine speed tends to fall, causing the balls to move inward and increase the fuel supply. Because the equilibrium speed remains constant, the correction happens immediately, maintaining uniform speed.

Characteristics of Isochronous Governor

1. Zero speed range: The minimum and maximum equilibrium speeds are the same; hence the speed range is zero.
2. Constant equilibrium speed: The governor operates at one constant speed irrespective of load changes.
3. High sensitivity: It can detect very small changes in speed and respond quickly.
4. Possibility of hunting: Due to extreme sensitivity, the governor may become unstable if damping is not provided.
5. Ideal behavior: In practice, perfect isochronism is difficult to achieve due to friction and mechanical imperfections.

Construction and Working

An isochronous governor can be achieved in spring-loaded governors like the Hartnell governor by adjusting the spring stiffness and initial tension such that the controlling force curve becomes a straight line passing through the origin. In this condition, the controlling force is proportional to the square of the speed.

When the engine runs at the designed speed, the centrifugal force on the balls is balanced by the spring force or controlling force. When there is a change in load, the governor immediately moves the sleeve up or down to correct the fuel supply so that the speed remains constant. Since the equilibrium speed does not change, all positions of the sleeve correspond to the same engine speed, which is the key feature of the isochronous governor.

Advantages of Isochronous Governor

1. Constant speed operation: It maintains an absolutely uniform speed, which is important in generators and precision machines.
2. Quick response: It reacts instantly to small speed variations due to high sensitivity.
3. Efficient fuel control: It provides accurate fuel regulation and minimizes waste.

Disadvantages of Isochronous Governor

1. Hunting tendency: The governor may cause speed oscillations if there is no proper damping mechanism.
2. Difficult to achieve practically: Perfect isochronous conditions are rare due to friction and spring imperfections.
3. Unsuitable for large engines: Large load changes require small speed variations for stable operation, which is not possible in an isochronous system.

Applications

Isochronous governors are used in high-speed engines, electric generators, and turbines where constant speed is crucial for performance and synchronization. Modern electronic control systems often use the principle of isochronism to maintain precise speed regulation.

Conclusion:

An isochronous governor is a highly sensitive type of governor designed to maintain a constant engine speed under all load conditions. It eliminates the range of speed variation, ensuring steady operation. However, due to its over-sensitivity, it may cause hunting, and hence, damping is necessary for stability. Despite this limitation, it remains an important concept in precise speed control systems used in modern engineering applications.