Mechanical Governors

What is a mechanical governor?

10 min readJun 18, 2022

A Governor is a mechanical device used to govern the speed of machines. From small engines to tractors to standby power systems even your automobiles are enabled with governors to regulate their speed. It allows the engine to run at the speed you select, without any effect of changing the load.

With the continuous change of load, the configuration of the governor varies, which helps to control the supply of fuel required by the engine. In simple words, a Mechanical Governor is a speed control device, with suspended masses that respond to the changing speed with the help of inertia.

Functions of a governor:

The functions of a governor is to regulate the mean speed of an engine, when there are variations in the load.
When the load on an engine increases, its speed decreases, therefore it becomes necessary to increase the supply of working fluid.
On the other hand, when the load on the engine decreases, its speed increases and thus less working fluid is required.
The governor automatically controls the supply of working fluid to the engine with the varying load conditions and keeps the mean speed of the engine within certain limits.

Types of Governors:

Governors are mainly divided into two types, although they are further subdivided into several parts.

Two main types of governors are following

Centrifugal governor
Inertia governor
Hydraulic governor
Pneumatic governor

1)Centrifugal Governor

Centrifugal Governor only centrifugal force and change in speed are responsible for controlling the actions. It is widely used due to the variety of applications and mostly preferred when balance on the masses is needed in the operation.

Principle:

It works on the principle of balancing centrifugal force of the rotating balls.

Construction:

A Centrifugal Governor has a simple design. This type of governor has multiple masses known as governor balls which rotate at the distance from the axis of a shaft and driven through suitable gearing from the engine crankshaft. It has two balls of equal masses attached to the arm. These balls are provided by the combination of dead weight or spring. Spindle axis is connected to the sleeve and driven by a bevel gear mechanism connected with the crankshaft. Throttle valve is connected to the sleeves and operated by the actual change of speed of the engine. As load increases speed decreases and the speed of governor ball as well as governor also decreases which is geared with the crankshaft.

Working:

It works as the mechanical link between the throttle which is responsible for fuel supply and the speed. The governor balls revolve with spindles and create a centrifugal force in the inward direction which is generally known as the controlling force. A governing action depends upon the change of speed and centrifugal force provided by the balls. As soon as the throttle valve opens it increases the supply of fluid increasing speed of the engine. The inward and upward movement of the ball is transmitted by the governor sleeve to the throttle valve which controls the amount of fuel supplied to the engine. As soon as the shaft rotates, the object starts rotating around the shaft and goes away from it due to the action of centrifugal force which operates the throttle valve.

Applications

1. It limits the rotation speed in the internal combustion engine of automobiles and keeps it controlled according to desired speed.

2. It is used to control the speed of the turbine shaft in a Hydro-electric power plant.

3. Centrifugal governors are also used to control the speed of mechanical music boxes.

2)Inertia governor

Inertia governors are quite different from centrifugal governors because they work on different principles. The Governor balls are arranged such the inertia force generated from the angular acceleration of the Governor shaft tend to vary their positions. The displacement of the balls is controlled by Spring and the mechanism of governor. Through this the availability of air fuel mixture are often controlled. In this governor the positions of the balls depends on the speed of change of speed of the Governor shaft. Because of this the quick response will be obtained as we change the load. This type of governor takes action thanks to acceleration and undue to finite change in speed.

Centrifugal governor is preferred over inertia governor because inertia governors have practical difficulty of arrangements and expected balance of revolving parts.

3)Hydraulic Governor

Hydraulic Governor is one of the types of governor. Alike a Mechanical type, Hydraulic Governor is an all-speed governor, which means that the governor is in control during the entire rack and not directly by the accelerator to the supply to maintain the speed, regardless of the power that needs from moment to moment.

Construction of Hydraulic Governor

The Construction of Hydraulic Governor is not as easy as the Mechanical Governor due to the number of components involvement and its working principle. The construction of hydraulic type of governor consists of Speeder Spring, Fly Weights, Oil Inlet, Oil Outlet, Servo Piston, Hydraulic Oil, Pilot Valve

You can see how the parts are constructed in the above image.

The balanced mechanism of a hydraulic governor is connected to a control valve rather than the fuel that controls racks directly, as in a mechanical governor.
This valve is in charge of directing hydraulic fluid, which regulates the fuel racks and, as a result, the engine’s power or speed decreases and increases. Due to the increasing flow of fuel, greater force is created and vice versa.

Working of Hydraulic Governor

The operational agent in a mechanical governor is the centrifugal force, but in the Hydraulic Governor, the pressure differential of the Hydraulic across an orifice is the operational agent in the Carburetor.
In a hydraulic governor to pass the oil flow from a positive oil pump is operated by an Engine. The pressure differential varies in proportion to the square of the engine speed. At equilibrium, it is governed by the driver’s foot pressure on the accelerator pedal.
Hydraulic governors remove the drive’s strong mechanical forces bearing loads and potential torsional vibrations. As a result, they outperform mechanical governors.
Once the load is increased, the Flyweights will lift the spindle and allows the hydraulic to flow into the piston.
Now, the piston will move upwards and allows the throttle valve in the carburetor to open, which allows the more fuel to supply to the engine. Due to which the engine receives more fuel supply and able to overcome the load and increases the speed of the whole vehicle.

The advantages of Hydraulic Governors

They provide a high output power.
They have a high level of accuracy and precision.
They are highly efficient.
Hydraulic governors are simple to maintain.
This type of automobile governor is used in medium to large size engines.
Hydraulic governor has low-cost and basic and basic design.

4)Pneumatic Governor

A Pneumatic governor, also known as flap valve governor is often employed to control fuel injection of an IC engine. Pneumatic Governor is an all-speed type of governor. It regulates an engine’s whole speed range. The Venturi effect governs the operation of these automobile governors. They respond to the velocity of air in the engine’s intake manifold.

Construction of Pneumatic Governor

The pneumatic governor is composed of two major components.

Venturi Section Attached To The Air Intake Manifold — This portion monitors the airflow velocity and generates a vacuum based on it. It has a butterfly valve attached to the accelerator pedal.
Diaphragm Unit Installed On The Fuel Injection Line — A diaphragm device installed on the end of the fuel pump can manage the fuel delivery based on the rise or decrease in vacuum created by the Venturi Unit. A spring is attached to one side of the diaphragm, while a control rod is attached to the other.

Other than these two major components, there are other different parts like Diaphragm Unit, Diaphragm, Diaphragm Spring, And Few others

The Pneumatic Governor is directly connected to the Carburetor. Whenever the load is increased and there is requirement of more fuel supply; the pneumatic governor creates the vacuum and able to open the throttle valve. Due to which the valve opens and allows the more fuel to supply into the injector or engine.

Working of Pneumatic Governor

The velocity of airflow in an engine’s intake manifold varies with engine speed. When the engine is stopped, the spring pushes against the diaphragm, keeping the fuel supply entirely open, that is maximum fuel supply position. When the engine is operating, the vacuum generated determines the location of the diaphragm and hence the fuel delivery.
As the engine speed increases, the load on the engine lowers. The bigger the air intake, the greater the engine speed. This raises the suction generated by the Venturi section installed on the intake manifolds.
The vacuum formed in the venturi portion drew the diaphragm and control rod together, which leads to immediate cut off of the gasoline supply. This reduction in fuel supply gradually reduces an engine’s speed.
When a motor vehicle’s accelerator pedal is pressed, the butterfly valve opens, allowing more air to flow through it. It does, however, reduce airflow via the auxiliary venturi device, which controls fuel delivery that results in more fuel supply. Likewise, depressing the accelerator closes the butterfly valve while increasing airflow via the venturi unit which results in less fuel supply.

The advantages of Pneumatic Governor are

It has an Outstanding sensitivity.
Pneumatic governors have shown to be most effective in small and medium-sized engines.
They are sensitive to torque loading fluctuations and provide reliable idling control.

The disadvantages of Pneumatic Governor are

Hydraulic governors are oversensitive at higher speeds. This might result in an abrupt shift in engine torque.
This type of automobile governors may sometimes cause leakage.
The density of the air influences the flow velocity

What Are Digital Governors?

On the opposite hand, digital governors are supported one hardware platform, which makes them much more convenient. Basically, these are speed control units that provide accurate and efficient speed control, with in no time response to load changes.

Advantages of Digital Governors:

· They are created to withstand severe environments

· They are very durable in the long run

· They are designed to regulate motor speed and aren’t subject to drift.

· The Hydro digital governor also comes with a back-up speed and creep detection system that makes the device even more reliable.

Application of governor mechanism for engine :

Fig 7: Governor used in engine, image source -learnmech.com

Figure shows a sketch of a governor along with linkages which regulates the supply to the engine. The governor shaft is rotated by the engine.

If the load on the engine increases the engine speed tends to reduce, as a result of which governor balls move inwards. This causes the sleeve to move downwards and this movement is transmitted to the valve through linkages to increase the opening and, thereby, to increase the supply.
On the other hand, a reduction in the load increases engine speed. As a result of which the governor balls try to fly outwards. This causes an upward movement of the sleeve and it reduces the supply.
Thus, the energy input (fuel supply in IC engines, steam in steam turbines, water in hydraulic turbines) is adjusted to the new load on the engine. Thus the governor senses the change in speed and then regulates the supply.

Due to this type of action it is a simple example of a mechanical feedback control system which senses the output and regulates input accordingly.

Difference between flywheel and governor:

Many people confuse flywheels and governors, but they are totally two different things. Here are some differences between them.
A flywheel is used to mitigate cyclic fluctuations in available energy but a governor is used to adjust the supply of fuel as per the load.
The energy stored in the flywheel is kinetic which is 100% available but the governor mechanism involves friction.
The flywheel is not used when cyclic fluctuation of energy is small or negligible.
While a governor is necessary for all the types of engines because it limits the fuel supply as per demand.
If we have constant load then the governor will remain idle but due to cyclic fluctuations in energy available, the flywheel will always work.
Governor has no influence on cyclic fluctuations in energy and flywheel has no influence on the mean speed of an engine.
Governor controls mean speed of the engine and flywheel controls cyclic fluctuations in energy.