What is Engine Governor?
A governor, or speed limiter or controller, is a device used to measure and regulate the speed of a machine, such as an engine.
A classic example is a centrifugal governor, also known as the Watt or fly-ball governor on a reciprocating steam engine, which uses the effect of inertial force on rotating weights driven by the machine output shaft to regulate its speed by altering the input flow of steam.
An Engine governor is a device that automatically maintains the rotary speed of an engine or other prime mover within reasonably close limits regardless of the load. A typical governor regulates an engine’s speed by varying the rate at which fuel is furnished to it.
Nearly all governors depend for their action on centrifugal force and consist of a pair of masses rotating about a spindle driven by the prime mover and kept from flying outward by a controlling force, usually applied by springs.
With an increase in speed, the controlling force is overcome and the masses move outward; the movement of the masses is transmitted to valves supplying the prime mover with its working fluid or fuel. The revolving masses are balls attached to a vertical spindle by link arms, and the controlling force consists of the weight of the balls.
If the load on the engine decreases, the speed will increase, the ball M will move out, and member C will slide up the vertical spindle and reduce the steam admitted to the engine, thus reducing the speed. An increase in the load will have the opposite effect.
Modern governors are used to regulating the flow of gasoline to internal combustion engines and the flow of steam, water, or gas to various types of turbines.
Types of Governors
Following are the three different types of governors used in automobile vehicles:
- Mechanical or centrifugal governor.
- Pneumatic governor.
- Hydraulic governor.
1. Mechanical or Centrifugal Governor
These governors consist of weighted balls, or flyweights, that experience a centrifugal force when rotated by the action of the engine crankshaft. This centrifugal force acts as the controlling force and is used to regulate the fuel supplied to the engine via a throttling mechanism connected directly to the injection racks.
These weight assemblies are small and hence the force generated is not enough to control the injection pumps of large engines. They can be used where exact speed control is not required. They have a large dead band and have small power output.
Working of Mechanical Governor
When the engine starts, the weights take up a position to maintain a stable idling speed. As the accelerator pedal is depressed against the spring, the weight moves inwards, and since the weight is linked to the control rod, the fuel delivery is increased and hence the engine speed also increases.
The increased engine speed causes the pump camshaft to rotate faster, which moves the weights outward against the action of control springs, reducing the fuel delivery until the correct balance is arrived at for a particular engine operating condition.
Thus, the accelerator does not increase delivery directly but delays the action of the governor. The relative position of governor-weight and control-rod positions when the engine is at idling and full-load positions.
Advantages of mechanical governors
- They are cheap.
- They can be used when it is not necessary to maintain an exact speed depending on the load.
- They are simple in construction and have only a few parts.
2. Pneumatic Governor
Pneumatic governors are most successfully used in small and medium-sized engines. They are sensitive to variations in torque loading and ensure stable idling control. As with pneumatic induction pipe control, the air supply at light loads is throttle by a butterfly valve placed in a choke.
This valve is directly operated by the accelerator pedal. The throttle unit is placed between the air cleaner and the entry to the inlet manifold. Which results in reduced air pressure at the end of induction.
Injection then takes place into less dense air than with unrestricted induction, and the control thus becomes quantity rather than quality control. The fuel injection is controlled by the depression at the choke to a diaphragm chamber mounted on the end of the injection pump.
The diaphragm plate is mounted on the end of the control rack of the pump. It is pushed to the full load position (to the right) by the main control spring. Again, the increased depression at the throttle arises when the accelerator pedal is released. It will pull the diaphragm and control rod to the left, thus reducing the fuel supply.
An auxiliary spring is also used to balance the height depression at idling speed. It is brought into action progressively by the action of a cam.
3. Hydraulic Governor
Hydraulic governors eliminate the high mechanical forces bearing loads and possible torsional vibrations in the drive. And, hence they are preferred over mechanical governors.
In a mechanical governor, the operative agent is the centrifugal force which governs the speed. In a hydraulic governor, it is the pressure difference across an orifice required to pass the oil flow from a positive oil pump driven by an engine.
The pressure difference varies as the square of the engine speed. And it is determined at equilibrium by the pressure of the driver’s foot on the accelerator pedal.
A hydraulic governor, like a mechanical governor, is an all-speed governor i.e., the governor is in control throughout the whole rack is operated by the governor and not directly by the accelerator to the supply to maintain the speed, no matter what the power requirements may be from moment to moment.
Advantages and Disadvantages of Hydraulic Governors
- They have a high-power output,
- They have high accuracy and precision
- They have high efficiency
- Maintenance of hydraulic governors is easy