Posted tagged ‘diesel engine’
Frequently Asked Interview Questions for Mechanical Engineers!!
September 18, 2011MECHANICAL GOVERNORS
September 13, 2011
This Meeting Guide is the third in a series dealing with the basic
diesel engine fuel system and components. It is about the diesel
governor.

Diesel engines can accelerate-increase speed-at the rate of more
than 2000 revolutions per second. Yes, PER SECOND. Without a
governor a diesel engine can quickly destroy itself.

you were to move the fuel rack of a diesel engine to the full “ON”
position without a load and with the governor not connected, the
engine speed might climb and exceed safe operating limits before
you could shut it down. One second…two seconds…before you
knew what was happening, the engine may have been seriously
damaged by overspeeding.
This warning – never operate a diesel engine without a governor
controlling it – is concerned with one of the purposes of governors:
to prevent engine overspeeding. Governors also keep the engine at
the desired speed and increase or decrease engine power output to
meet load changes.

The mechanical governor is the simplest of the various types of
governors and is basic to their operation.
Besides the mechanical governor, Caterpillar engines use: servomechanical
governors, hydraulic governors and electronic
governors. These governors will be discussed in future
presentations.
governor control lever, the control linkage, the governor and the fuel
injection pump housing.

This is a closeup of the governor, mounted on the rear of the fuel
injection pump housing.
governor using schematic illustrations.
mechanisms: the speed measuring mechanism and the fuel changing
mechanism.
fuel supplied the engine to correct these changes.
Let’s look at each basic mechanism separately and learn how it
operates.

The speed measuring mechanism is simple, has few moving parts
and measures engine speed accurately. The main parts are:
flyweights move outward pivoting the ballarms upward. The amount
of outward force depends on the speed of rotation.
Centrifugal force is the basic operating principle of the speed
measuring mechanism. Now, what is centrifugal force?

If we tie a ball on a string . . . .
the ball. This centrifugal force swings the ball outward and upward
until the ball is nearly straight out.
And, we can see that the faster we swing it, the greater the pull on
the string and the farther outward it swings.
speed measuring operation of the diesel engine governor. Keep
centrifugal force in mind as we discuss the other parts of the speed
measuring mechanism. Remember, the greater the engine speed, the
greater the centrifugal force and, therefore, the greater the
movement of the flyweights and ballarms.

spring. The spring acts against the force of the rotating flyweights
and tends to oppose them. The force exerted by the spring depends
on the governor control setting.

the spring. The spring force opposes the flyweights to regulate the
desired engine speed setting.
The governor control, shown here as a simple push-pull knob, may
be a hand operated control lever or a foot operated accelerator
pedal.
As long as the spring force equals the flyweight centrifugal force,
engine speed remains constant.

speed changes. The fuel changing mechanism links the speed
measuring mechanism with the fuel injection pumps to control
engine.
speed changes, are transferred through the simple linkage to the
rack and, therefore, to the fuel injection pump plunger.
speed decreases. The flyweight force decreases, and the spring
moves the linkage and rack to increase the fuel to the engine. The
increase fuel position is held until the engine speed returns to the
desired setting, and the flyweight force again balances the spring
force.

force increases, overcoming the spring force, moving the rack to
decrease fuel to the engine. The decrease fuel position is held until
engine speed returns to the governor control setting, and the spring
force again balances the flyweight force.
drive gears, flyweights, spring, and control lever of the speed
measuring mechanism, and the connecting linkage, rack and fuel
injection pump of the fuel changing mechanism.

segments extends from the injection pump housing into the
governor. The rack and fuel injection pumps are parts of the fuel
injection pump housing assembly.
fuel injection pump operation and how the fuel injected into each
cylinder is increased or decreased.

that the rack extends into the governor. Rack movement controls the
amount of fuel injected in each cylinder.
Let’s look at a closer view of our cutaway governor.
spring seat and thrust bearing. The thrust bearing (not previously
mentioned) is an anti-friction bearing between the flyweight
ballarms which rotate and the spring seat which, of course, does not
rotate.

pump camshaft.
The control lever has been removed from its shaft in the governor
housing and set in place to show how it is positioned.
flyweights , spring, spring seats, control lever and the collar and bolt
which connects to the rack. The purpose of the collar is explained
later.
spring, (4) spring seat and thrust bearing and (5) flyweight
assembly.
The arrows indicate drive gear rotation and rack movement.
between LOW IDLE position and the HIGH IDLE position.
The low idle stop and high idle stop are simply minimum and
maximum engine rpm settings with no load on the engine.

prevent them from turning after they are adjusted.
low idle, high idle or fuel off.

spring loaded plunger in the lever assembly contacts the low idle
stop of the adjusting screw.
lever contacts the high idle adjusting screw.

– past . . . .
shoulder on the low idle screw . . .

The low idle and high idle screws, then limit minimum and
maximum engine rpm with no load on the engine. What limits
engine power output when the engine is fully loaded?

output. The collar is secured by a bolt connecting the rack linkage.
The stop bar is mounted in the governor housing. With the rack
moved to the FULL LOAD position, the collar just contacts the stop
bar.

picks up a load, the speed decreases, flyweight centrifugal force
lessens, and the spring moves the rack to give the engine more fuel
increasing power. The collar (2) and stop bar (3) limit the distance
the spring can move the rack. As the collar contacts the stop bar,
full load position is reached. This limits the fuel delivered to the
engine so as not to exceed design limitations.

Like other diesel engine components, the governor must be
lubricated for long life. Let’s look at a governor lubrication system
schematic.
from the diesel engine oil manifold is directed to the governor drive
bearing. All other governor parts are lubricated by splash.
The oil drains from the governor, through the fuel injection pump
housing, back to the engine crankcase.

In summary, we have discussed the mechanical governor’s primary
components and principle of operation. Remember a governor has
two basic mechanisms: the speed measuring mechanism and the
fuel changing mechanism.
flyweights, thrust bearing, drive gears and rack. We also discussed
the high and low idle settings and the full load stop.
At the beginning of this lesson we warned: NEVER OPERATE A
DIESEL ENGINE WITHOUT A GOVERNOR CONTROLLING
IT. Why are governors so important to a diesel engine?
Note: The instructor should make clear we are not saying
gasoline engines never have a governor. Some
gasoline engines use a governor for the same reasons as
First, gasoline engines are self-limiting. Engine speed is controlled
by a butterfly valve in the intake manifold which limits the air
supply Limiting the amount of air taken in for combustion, limits
engine speed.

not limited, and the cylinders always have more air than is needed
to support combustion. The amount of fuel injected into the
cylinders controls engine speed.

into the air intake manifold, engine response is immediate. This,
resulting greater power stroke, adds up to very rapid acceleration.
As we said earlier, diesel engines can accelerate at a rate of more
than 2000 revolutions per second. Because of this rapid
acceleration, manual control is difficult, if not impossible.

This governor works fine on engines whose engine speed is held
fairly constant and the governor is controlled by hand. However, on
other engines, the force needed to compress the governor spring or
to move the rack -just operating the governor – could be very tiring
to the operator.
compressing the governor spring is done with engine oil pressure.

injection pump rack is done with engine oil pressure.
These governors are discussed in . . . .
Governor
September 8, 2011A governor is essentially a speed-sensitive device, designed to maintain a constant engine speed regardless of load variation. Since all governors used on diesel engines control engine speed through the regulation of the quantity of fuel delivered to the cylinders, these governors may be classified as speed-regulating governors. As with the engines themselves there are many types and variations of governors. In this module, only the common mechanical-hydraulic type governor will be reviewed.
The major function of the governor is determined by the application of the engine. In an engine that is required to come up and run at only a single speed regardless of load, the governor is called a constant-speed type governor. If the engine is manually controlled, or controlled by an outside device with engine speed being controlled over a range, the governor is called a variable speed type governor. If the engine governor is designed to keep the engine speed above a minimum and below a maximum, then the governor is a speed-limiting type. The last category of governor is the load limiting type. This type of governor limits fuel to ensure that the engine is not loaded above a specified limit. Note that many governors act to perform several of these functions simultaneously.
Operation of a Governor
The following is an explanation of the operation of a constant speed, hydraulically compensated governor using the Woodward brand governor as an example. The principles involved are common in any mechanical and hydraulic governor.
The Woodward speed governor operates the diesel engine fuel racks to ensure a constant engine speed is maintained at any load. The governor is a mechanical-hydraulic type governor and receives its supply of oil from the engine lubricating system. This means that a loss of lube oil pressure will cut off the supply of oil to the governor and cause the governor to shut down the engine. This provides the engine with a built-in shutdown device to protect the engine in the event of loss of lubricating oil pressure.
Simplified Operation of the Governor
The governor controls the fuel rack position through a combined action of the hydraulic piston and a set of mechanical flyweights, which are driven by the engine blower shaft.
Figure 28 provides an illustration of a functional diagram of a mechanical-hydraulic
governor. The position of the flyweights is determined by the speed of the engine. As
the engine speeds up or down, the weights move in or out. The movement of the
flyweights, due to a change in engine speed, moves a small piston (pilot valve) in the
governor’s hydraulic system. This motion adjusts flow of hydraulic fluid to a large
hydraulic piston (servo-motor piston). The large hydraulic piston is linked to the fuel
rack and its motion resets the fuel rack for increased/decreased fuel.

Fig 28 simplified Mechanical-Hydraulic Governor
With the engine operating, oil from the engine lubrication system is supplied to the
governor pump gears, as illustrated in Figure 29. The pump gears raise the oil pressure to a value determined by the spring relief valve. The oil pressure is maintained in the annular space between the undercut portion of the pilot valve plunger and the bore in the pilot valve bushing. For any given speed setting, the spring speeder exerts a force that is opposed by the centrifugal force of the revolving flyweights. When the two forces are equal, the control land on the pilot valve plunger covers the lower ports in the pilot valve bushing.

Fig 29 Cutway of Woodward Governor
When the engine load increases, the engine starts to slow down in speed. The reduction in engine speed will be sensed by the governor flyweights. The flyweights are forced inward (by the spring), thus lowering the pilot valve plunger (again, due to the downward spring force). Oil under pressure will be admitted under the servo-motor piston (topside of the buffer piston) causing it to rise. This upward motion of the servo-motor piston will be transmitted through the terminal lever to the fuel racks, thus increasing the amount o f fuel injected into the engine. The oil that forces the servo-motor piston upward also forces the buffer piston upward because the oil pressure on each side of the piston is unequal.
This upward motion of the piston compresses the upper buffer spring and relieves the pressure on the lower buffer spring.
The oil cavities above and below the buffer piston are common to the receiving
compensating land on the pilot valve plunger. Because the higher pressure is below the compensating land, the pilot valve plunger is forced upward, recentering the flyweights and causing the control land of the pilot valve to close off the regulating port. Thus, the upward movement of the servo-motor piston stops when it has moved far enough to make the necessary fuel correction.
Oil passing through the compensating needle valve slowly equalizes the pressures above and below the buffer piston, thus allowing the buffer piston to return to the center position, which in turn equalizes the pressure above and below the receiving
compensating land. The pilot valve plunger then moves to its central position and the
engine speed returns to its original setting because there is no longer any excessive
outward force on the flyweights.
The action of the flyweights and the hydraulic feedback mechanism produces stable
engine operation by permitting the governor to move instantaneously in response to the load change and to make the necessary fuel adjustment to maintain the initial engine speed.
SKYACTIV TECHNOLOGY
August 23, 2011Highlights of the SKYACTIV technologies:
-
SKYACTIV-G: a next-generation highly-efficient direct-injection gasoline engine with the world’s highest compression ratio of 14.0:1
-
SKYACTIV-D: a next-generation clean diesel engine with the world’s lowest compression ratio of 14.0:1
-
SKYACTIV-Drive: a next-generation highly-efficient automatic transmission
-
A next-generation manual transmission with a light shift feel, compact size and significantly reduced weight
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A next-generation lightweight, highly-rigid body with outstanding crash safety performance
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A next-generation high-performance lightweight chassis that balances precise handling with a comfortable ride
– First product to be equipped with SKYACTIV technology will be a Mazda Demio featuring an improved, fuel-efficient, next-generation direct-injection engine that achieves fuel economy of 30 km/L.
Overview of the SKYACTIV technologies
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A next-generation highly-efficient direct-injection gasoline engine that achieves the world’s highest gasoline engine compression ratio of 14.0:1 with no abnormal combustion (knocking)
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The world’s first gasoline engine for mass production vehicles to achieve a high compression ratio of 14.0:1
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Significantly improved engine efficiency thanks to the high compression combustion, resulting in 15 percent increases in fuel efficiency and torque
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Improved everyday driving thanks to increased torque at low- to mid-engine speeds
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A 4-2-1 exhaust system, cavity pistons, multi hole injectors and other innovations enable the high compression ratio
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A next-generation clean diesel engine that will meet global emissions regulations without expensive NOx after treatments — urea selective catalytic reduction (SCR) or a Lean NOx Trap (LNT) — thanks to the world’s lowest diesel engine compression ratio of 14.0:1
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20 percent better fuel efficiency thanks to the low compression ratio of 14.0:1
-
A new two-stage turbocharger realizes smooth and linear response from low to high engine speeds, and greatly increases low- and high-end torque (up to the 5,200 rpm rev limit)
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Complies with global emissions regulations (Euro6 in Europe, Tier2Bin5 in North America, and the Post New Long-Term Regulations in Japan), without expensive NOx after treatment
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A next-generation highly efficient automatic transmission that achieves excellent torque transfer efficiency through a wider lock-up range and features the best attributes of all transmission types
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Combines all the advantages of conventional automatic transmissions, continuously variable transmissions, and dual clutch transmissions
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A dramatically widened lock-up range improves torque transfer efficiency and realizes a direct driving feel that is equivalent to a manual transmission
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A 4-to-7 percent improvement in fuel economy compared to the current transmission
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A light and compact next-generation manual transmission with crisp and light shift feel like that of a sports car, optimized for a front-engine front-wheel-drive layout
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Short stroke and light shift feel
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Significantly reduced size and weight due to a revised structure
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More efficient vehicle packaging thanks to its compact size
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Improved fuel economy due to reduced internal friction
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A next-generation lightweight, highly-rigid body with outstanding crash safety performance and high rigidity for greater driving pleasure
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High rigidity and lightness (8 percent lighter, 30 percent more rigid)
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Outstanding crash safety performance and lightness
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A “straight structure” in which each part of the frame is configured to be as straight as possible. Additionally, a “continuous framework” approach was adopted in which each section functions in a coordinated manner with the other connecting sections
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Reduced weight through optimized bonding methods and expanded use of high-tensile steel
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A next-generation high-performance lightweight chassis that balances precise handling with a comfortable ride feel to realize driving pleasure
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Newly developed front strut and rear multilink suspension ensures high rigidity and lightness (The entire chassis is 14 percent lighter than the previous version.)
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Mid-speed agility and high-speed stability — enhanced ride quality at all speeds achieved through a revision of the functional allocation of all the suspension and steering components
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