The governor is an automatic adjusting device that automatically increases or decreases the fuel supply of the fuel injection pump according to the change of the diesel engine load, so that the diesel engine can run at a stable speed.
The governor has been widely used in industrial DC motor speed regulation, industrial conveyor speed regulation, lighting and lighting mediation, computer power supply cooling, DC fan, etc.
Mode of operation
The governor is used to reduce the automatic adjustment of non-periodic speed fluctuations in some machines.
Keep the machine speed constant or close to the set value.
Unlike turbines, turbines, steam turbines, gas turbines, and internal combustion engines do not automatically adapt their output torque to their own load changes, so when the load changes, the units driven by them lose stability.
This type of unit must be equipped with a governor to enable it to establish an adaptive relationship between the load and the energy supply at any time in accordance with conditions such as load to ensure proper operation of the unit.
The theoretical and design issues of the governor are the research content of mechanical dynamics.
There are many types of governors.
One of the most widely used is the mechanical centrifugal governor.
The governor with a tachogenerator or other electronic device as a sensor has been widely used in various industrial sectors.
The governor must meet the stability conditions:
① When the unit speed deviates from the set value, the governor can respond accordingly, and at the same time, there must be a repetitive force that often acts to return the governor to the initial state.
The spring in the centrifugal governor is the part that produces restoring force.
Such a governor is called a statically stable governor.
However, statically stable governors may also exhibit dynamic instability during the adjustment process.
When the adjustment is excessive and the reverse adjustment occurs, the actual adjustment action forms an oscillation process.
The governor that makes the oscillations decay quickly is called a dynamically stable governor, otherwise it is a dynamically unstable governor, which does not guarantee the normal operation of the machine.
② Increasing damping in the conditioning system is one way to improve dynamic stability.
Damping in the adjustment system, such as friction in the motion pair, makes the governor a certain insensitivity, that is, when the speed of the controlled shaft deviates slightly from the set value, the governor does not generate a corresponding action.
The insensitivity of a mechanical governor is typically about 1% of its set point.
Excessively sensitive governors will also have unacceptable adjustments due to periodic speed fluctuations during normal operation of the unit.
The governor is used to keep the speed of the diesel engine stable.
During the change of the load of the diesel engine, its rotational speed will change accordingly.
When the speed is reduced, if the governor is not adjusted, the diesel will eventually stop.
When the speed increases, if the governor does not work, the diesel engine will eventually be unable to withstand excessive centrifugal force and be damaged.
The role of the governor is to keep the speed of the diesel engine stable.
In addition, the governor can maintain the minimum speed and maximum speed of the diesel engine to prevent “speeding” during low-speed operation and “speeding” during high-speed operation, resulting in mechanical damage.
According to its working principle, it can be divided into:
- Mechanical and pneumatic composite
- Mechanical hydraulic composite
- Electronic, etc.
However, the most widely used one is the mechanical governor, which has a simple structure, reliable operation and good performance.
The hydraulic governor adds a hydraulic amplifying element (hydraulic servo) between the sensing element and the oil quantity adjusting mechanism, so that the output signal of the sensing element is transmitted to the oil quantity adjusting mechanism through the amplifying element, so it is also called indirect action type adjustment governor.
The hydraulic amplifying element has an amplification and execution function, and is mainly composed of two parts of control and execution.
- Hydraulic governor without feedback
Its working principle is as follows:
When the load is reduced, the rotational speed of the drive shaft driven by the crankshaft is increased, the centrifugal force of the flying ball is increased, and the speed lever is pushed to the right.
Then, the rocker rotates counterclockwise around point A, the spool moves to the right, and the pressurized oil enters the right space of the servo cylinder.
At the same time, the left space of the cylinder communicates with the low-pressure oil passage through the oil hole, and the oil therein is discharged.
Under the action of the pressure difference, the servo piston drives the fuel pump rack to the left to reduce the oil supply.
When the speed returns to the original value, the spool valve also returns to the center position and the adjustment process ends.
When the load increases and the speed decreases, the speed control process proceeds in the opposite direction.
From the above analysis, the centrifugal force generated by the governor flying ball is only used to push the slide valve, so the weight of the flying ball can be made smaller.
As the force of the hydraulic servo of the amplifier, different sizes of servo pistons and different oil pressures can be selected to amplify as needed.
However, in such a governor, since the sensing element directly drives the spool valve, it is difficult to accurately return to the original position and close the oil hole regardless of which direction it is moving.
This makes the engine speed unstable and causes severe fluctuations.
In order to make the governor stable, a device is added to the governor.
Its function is to counteract the slide valve while the servo piston is moving, moving it to the equilibrium position, reducing the possibility of diesel engine speed fluctuation.
This type of device is called a feedback mechanism.
- Hydraulic governor with rigid feedback mechanism
Its construction is basically the same as the above-mentioned non-feedback hydraulic governor.
Only the upper end A of the lever sense AC is not attached to the fixed hinge but to the piston rod of the servo piston.
This change causes the relationship between the sensing element, the hydraulic amplifying element, and the oil amount adjusting mechanism to change as follows.
When the load is reduced, the engine speed is increased, and the flying ball is opened outward to drive the speed lever to move to the right.
At this time, the servo piston has not yet operated, so the upper end point A of the feedback lever AC temporarily serves as a fixed point.
The lever rotates counterclockwise around A to drive the spool to the right to open the control hole. The high pressure oil enters the right chamber of the power cylinder, and the left chamber communicates with the low pressure oil passage.
This high-pressure oil pushes the servo piston to move the fuel injection rod to the left and reduces the fuel supply according to the new load.
While the servo piston is moving to the left, the lever AC swings to the left at point C and the spool connected to point B also moves to the left, thereby moving the spool in the opposite direction.
Thus, a lever device that can adversely affect the movement of the spool when the servo piston moves is referred to as a rigid feedback system.
When the adjustment process is finished, the spool returns to the starting position, closing the control oil hole and cutting off the oil path to the servo cylinder.
At this point, the servo piston stops moving, and the fuel pump adjustment lever moves to a new equilibrium position, and the engine operates under the corresponding new load.
Therefore, the governor has different steady speeds corresponding to different loads of the engine.
Because the fuel supply needs to be changed when the engine load changes, the position of point A changes with the load.
The point B connected to the spool valve should be in the original position under any stable conditions, regardless of the load.
Thus, the position of point C must be changed correspondingly to point A, thus causing a change in the rotational speed.
If the load is reduced, after the speed control process is finished, when the spool returns to the original position, the servo piston is at the position of reducing the fuel supply, so that point A is to the left and point C is to the right, because point C is to the right, the spring is further Under pressure.
Only at a slightly higher speed can the centrifugal force of the flying ball be balanced with the spring pressure.
This shows that after the steady operation of the load is reduced, the speed of the diesel engine is slightly higher than the original.
Similarly, when the load increases, after the stable operation, the speed of the diesel engine is slightly lower than the original.
The hydraulic governor with rigid feedback can ensure stable working characteristics of the speed regulation process.
However, after the load changes, the engine speed changes, and the steady rate t cannot be zero.
If the load change is required, the speed regulation process is stable, and the engine speed can be kept constant (ie, a hydraulic dispatcher with an elastic feedback system must be used.