Diesel fuel systems 357 Diesel fuel systems: general 358 Fuel injection systems 359 Fuel supply pumps 361 Fuel filters 363 Injectors 365 Types of injectors 366 Distributor injection pumps: axial type 369 Governor for axial pumps 371 Complete axial distributor pump 373 Distributor injector pumps: radial type 373 Radial pump schematic: operation 375 Commonrail injection systems 376 Injectors for commonrail systems 380 Basic inline injection pumps 382 Inline pump construction 383 Inline pump installation 384 Electronic diesel control 384 Injection pumps with electronic control 386 Technical terms 387 Review questions 387
Trang 1Diesel fuel systems
Chapter 19
Diesel fuel systems: general
Fuel injection systems
Fuel supply pumps
Fuel filters
Injectors
Types of injectors
Distributor injection pumps: axial type
Governor for axial pumps
Complete axial distributor pump
Distributor injector pumps: radial type
Radial pump schematic: operation
Common-rail injection systems
Injectors for common-rail systems
Basic in-line injection pumps In-line pump construction In-line pump installation Electronic diesel control Injection pumps with electronic control Technical terms
Review questions
Trang 2The correct operation of a diesel engine depends on its
fuel injection system, which must supply the
com-bustion chambers with just the right amount of fuel at
the right time The parts of the injection system that do
this are made with a high degree of accuracy and
operate with very small clearances.
This chapter will cover diesel fuel systems in
general and also provide an understanding of the
different types of injection systems – what they are and
how they function.
Diesel fuel systems: general
The locations of the parts of a diesel fuel system for a
light commercial vehicle are shown in Figure 19.1.
This has a fuel-supply system and an injection system.
Similar systems are used in four-wheel-drive vehicles
and in some passenger cars.
A schematic diagram of the system is shown in
Figure 19.2 The system includes the following parts,
although all these parts are not in the diagram.
1 Fuel tank – to hold distillate.
2 Fuel feed pump – to supply fuel from the fuel tank
to the injection pump.
3 Fuel filter – to filter minute particles from the fuel.
4 Sedimenter – to filter out water that might enter or condense in the system.
5 Injection pump – to deliver fuel at high pressure to the injectors at the right time.
6 Injector pipes – to connect the injection pump to the injectors.
7 Injectors – to spray fuel into the combustion chambers.
8 Overflow and leak-off pipes – to return excess fuel from the injection pump and the injectors to the tank.
9 Governor – to control the engine speed.
10 Control lever on the governor – connected to the driver’s accelerator.
figure 19.1 Location of the parts of a diesel fuel system in a light commercial vehicle FORD
Trang 3System operation
The system operates in the following way:
1 Fuel taken from the tank by the feed (supply) pump
passes through the sedimenter where water is
filtered out.
2 Fuel passes from the feed pump through the fuel
filter to the injection pump The feed pump does
not provide pressure, but keeps the system full.
A hand-priming pump on the top of the filter is used to prime and bleed the system.
3 The injection pump has a pumping element that
produces high pressure for the injectors It also
distributes high-pressure fuel to the injectors
through the injector pipes.
4 The injectors are operated by the high-pressure fuel
to spray fuel into the combustion chambers.
5 The injection pump has an internal vane pump
(feed pump) to provide a low pressure and to keep
the injection pump full The feed pump supplies
more fuel than is needed.
6 The surplus fuel is taken from the top of the pump
through the overflow pipe back to the fuel tank.
Circulation of the fuel cools and lubricates the
injection pump and also bleeds air from the system.
7 The leak-off pipe on the top of the injectors carries
a small quantity of fuel back to the fuel tank This
is fuel that leaks up inside the injector It is used to lubricate and bleed the injector before being returned to the fuel tank.
8 The engine speed and power is controlled by the accelerator and linkage, which is connected to the pump governor.
9 The fuel cut-off solenoid that is fitted to the injection pump is used to stop the engine When the engine switch is turned off, it cuts off the fuel to the pumping element.
■ The system has two main functions – fuel supply and fuel injection Some components are respons- ible for fuel supply and others are responsible for fuel injection.
Fuel injection systems
There are a number of different injection systems for diesel engines The main difference is that they have different types of injection pumps, although some are electronically controlled.
The types of injection systems are:
figure 19.2 Schematic arrangement of a fuel system with a distributor-type injection pump ZEXEL
injector
injection pipe
fuel tank sedimenter
VE injection pump
Trang 41 distributor pump systems
2 common rail, or accumulator, systems
3 in-line injection pump systems
4 unit-type systems.
Distributor pump systems and common-rail systems
are the most commonly used on engines in passenger
and light commercial vehicles In-line systems are now
used mainly on medium to heavy diesel engines and
unit-type injection systems are used on heavy diesels.
Distributor pump systems
The system previously described has an axial-type
distributor pump There are two designs of distributor
pumps: axial pumps and radial pumps These are the
types that are used on most light diesel engines.
Distributor pumps are designed for engines that
operate at relatively high speeds They have a single
pumping element, regardless of the number of
cylinders of the engine The pumping element and the
distributing arrangement are designed to suit the
number of cylinders of the engine.
The main difference in these two injection pumps is
the design of the high-pressure pumping element.
As the names suggest, the axial type has a pumping
plunger that acts axially, that is backwards and
forwards within the pump.
The radial type has a pumping element with
plungers that act radially, that is inwards and outwards
in relation to the centreline of the pump shaft.
■ The diagram in Figure 19.2 shows one injector
only; a four-cylinder engine would have four
injection pipes and four injectors.
Common rail systems
The arrangement of a common rail injection system is
shown in Figure 19.3 This has a low-pressure electric
pump in the fuel tank and a high-pressure fuel pump
that is driven by the engine The low-pressure pump
delivers fuel to the high-pressure pump, where the
pressure is increased to injection pressure A fuel line
connects the pump to the common fuel rail, and
injector pipes connect the common rail to the
injectors.
The injectors are fitted with an electric solenoid
that is controlled by an electronic control unit (ECU).
Electronic control opens and closes the injectors so
that they deliver a specified quantity of fuel at the right
time.
The system has a return line that returns surplus fuel from the top of the injectors, from the high- pressure pump and from the filter.
figure 19.3 Arrangement of a common rail fuel injection
system for a four-cylinder engine
injectors
fuel rail ECU
pump
filter
electric
In-line injection pump systems
The arrangement of a system with an in-line injection pump is shown in Figure 19.4 This has six separate pumping elements, one for each cylinder of the engine Injection pipes connect the pumping elements to the injectors In-line pumps are used with some light diesel engines and with many engines of commercial vehicles.
The in-line system shown has a supply pump mounted on the side of the injection pump It takes fuel from the tank and pumps it through the filters to the injection pump It also has an overflow line from the top of the filter to the tank, and a leak-off pipe from the injectors The fuel flow in the system is marked on the diagram.
Trang 5Unit injector systems
In these types of systems, the functions of the injection
pump element and the injector are combined within the
injector itself This enables the injectors to provide a
high-pressure charge of fuel and also to inject it as a
fine spray into the combustion chamber.
The injector is operated by a rocker arm and
pushrod by a cam on the engine’s camshaft Each
cylinder has its own injection unit.
The diagram in Figure 19.5 shows this type of
arrangement Fuel is taken from the tank by a transfer
pump It passes first through the primary filter, then
through the pump to the secondary filter, and on to the
injector At the appropriate time, the plunger of the
injector is operated by the rocker arm This pressurises
the fuel in the injector and the correct amount is
sprayed into the combustion chamber.
In this system, fuel at a low pressure is being
constantly circulated through passages in the cylinder
head This supplies the injectors with fuel and returns
the surplus to the fuel tank.
Fuel supply pumps
All diesel fuel systems have some form of supply
pump that takes fuel from the tank and delivers it to
the injection pump or, in the case of unit injectors, directly to the unit injector Vane pumps, diaphragm pumps, plunger pumps and gear pumps are all used, but this depends on the type of system.
■ Pumps that supply the low-pressure fuel are referred to as supply pumps feed pumps, lift pumps
or transfer pumps.
figure 19.4 Diagram of a fuel system with an in-line injection pump BOSCH
figure 19.5 Arrangement of a diesel fuel system with a
unit injector
Trang 6Vane pumps
Vane pumps are used with distributor-type injection
pumps The vane pump is located inside the injection
pump housing It is used to take fuel from the fuel tank
and supply it to the high-pressure pumping element.
The vane pump is driven by the injection pump
shaft (Figure 19.6) It has a rotor that is mounted
off-centre in the pump housing Slots in the rotor carry the
vanes, which slide backwards and forwards as the rotor
turns Fuel taken into the pump inlet is carried around
between the vanes and the body of the pump and
discharged from the outlet.
■ Vane pumps used with distributor-type pumps are
usually referred to as feed pumps.
Plunger pumps
Plunger pumps are used with in-line injection pumps.
They are often fitted to the side of the injection pump
and operated by a cam on the injection pump’s
camshaft (Figure 19.7).
The cam moves the plunger backwards and
forwards to take fuel in through the suction valve and
pump it out through the discharge valve, so
main-taining a flow of fuel.
Figure 19.8 illustrates plunger pump operation, as
follows:
1 Upstroke Fuel is forced through the discharge
valve into the outlet and also into the outer chamber
under the plunger.
2 Downstroke The plunger is forced down by the
spring, and fuel from the outer chamber is pumped
through the outlet At the same time, fuel is also
taken into the inner chamber through the suction valve.
3 Reduced stroke When the pressure beneath the plunger exceeds the spring pressure on top of the plunger, the stroke will be reduced The plunger will be held away from the pushrod, and its stroke will be reduced until the pressure under the plunger drops This is how pump pressure is controlled.
Priming pumps
Priming pumps are used during servicing to fill the system with fuel and to bleed air from the pump and injector pipes.
A hand-priming pump is fitted to the top of the supply pump on in-line injection systems This is operated by unscrewing the plunger and then moving it
up and down by hand In other systems, a separate hand pump can be fitted, or it can be combined with a filter (as shown in Figure 19.12).
Electric pumps
The common rail system uses an electric fuel pump (Figure 19.9) This is located inside the fuel tank and is used to supply low-pressure fuel to the main high- pressure pump.
The electric pump consists of an electric motor with permanent magnet fields connected to a roller-cell pump Fuel drawn into the pump passes through the body of the pump before leaving the tank.
figure 19.6 Arrangement of a vane-type feed pump,
used with a distributor-type injection pump
ZEXEL
figure 19.7 Plunger fuel supply pump BOSCH
Trang 7A pressure limiter, in the form of a spring-loaded
valve, opens when operating pressure is reached This
limits the pressure in the low-pressure side of the
system.
Fuel filters
Filtering of diesel fuel is most important because of the
very small clearances that exist between the working
parts in the injection pump and the injectors Diesel fuel must be clean.
The clearance between some injection parts is as little as 2 to 4 microns A micron is one-thousandth of
a millimetre (0.001 mm) To get some idea of the size
of the dust particles that need to be filtered out, Figure 19.10 compares the size of dust particles with a human hair A medium-sized particle that can be floating in the air has about one-tenth the diameter of the hair.
■ Care must be taken so that fuel put into the tank of
a vehicle is not contaminated in any way.
There are a number of different designs of filters, and they can be located in different parts of the system.
figure 19.8 Operation of a plunger-type supply pump ZEXEL
outer chamber
cam
inner chamber
discharge valve
suction valve
spring plunger
figure 19.9 Electric fuel pump for a common-rail
injec-tion system BOSCH
pump
commutator
figure 19.10 Size of dust particles compared with human
hair – D diameter of hair
Trang 8Filters can be fitted between the supply pump and the
tank, or between the supply pump and the injection
pump.
Faulty sealing of a filter on the suction side of a
supply pump will allow air to enter and fuel to leak,
while faulty sealing on the pressure side will allow fuel
to leak.
Filter with separate element
Figure 19.11 shows a fuel filter with a replaceable
element The filtering material is made of pleated
paper which will filter out very small particles.
Sedimenter
Figure 19.12(c) shows a sedimenter that has a away filter It has a filter canister similar to an engine- oil filter The sedimenter is serviced by fitting a new canister This also has a hand-priming pump.
throw-A sedimenter filters out water and small solid particles and these form sediment in the bottom of the filter bowl Most sedimenters are fitted with a switch that operates a warning light when the water in the filter reaches a certain level Water in a system can block filters and will cause considerable damage if it reaches the injection pump.
figure 19.11 Fuel filter with replaceable element
LUCAS/CAV
figure 19.12 Types of diesel fuel filters TOYOTA
Filter with glass bowl
The filter in Figure 19.12(a) has a glass bowl and a
filtering element The filter can be checked for
deposits or water by viewing through the clear glass
bowl The bowl can be removed for cleaning.
Water and sediment filters
Sedimenters, or sediment filters, are used to remove
water and sediment In Figure 19.12(b), a fuel filter
and a sedimenter are used side by side Any water in
the fuel is removed by the sedimenter before it
reaches the fuel filter A warning light is switched on
if the water level builds up in the bowl The sedimenter
shown is fitted with a hand-priming pump.
Trang 9The sedimenter in Figure 19.13 has a water-level
detector If the water level becomes too high, the float
will rise to operate the switch and light the warning
indicator.
■ Sediment is a collection of fine particles that settles
to the bottom of a liquid, in this case, water.
The filtering action of the sedimenter is as follows:
1 When the engine is running, fuel that enters the
sedimenter flows over the top of a cone, and this
acts as a diffuser to spread the fuel.
2 The fuel then passes down towards the bottom of
the sedimenter where it changes its direction and
flows upwards to the outlet.
3 As the fluid changes direction, any heavy particles
or water in the fuel fall to the bottom to remain as
sediment, and this can be drained off.
Combined filter and sedimenter
Figure 19.14 shows a compact design combined fuel
filter and sedimenter for a small vehicle It includes a
priming pump and a water-level warning sensor.
Injectors
Injectors come in various shapes and sizes The connection for the injection pipe can be at the top or at the side of the injector Injectors for engines of passenger cars and light commercial vehicles are either threaded and screwed into the cylinder head or secured
to the cylinder head with a clamp Other injectors have
a flange that is bolted to the cylinder head.
The nozzle at the lower end of the injector either fits against the combustion chamber, or projects slightly into it At the appropriate time, the nozzle directs a fine spray of fuel into the combustion chamber This occurs
at around 200 times a minute at engine idle, and up to around 2000 times a minute at high engine speed.
Injector operation
A simplified injector is shown in Figure 19.15 The operating parts are the needle, the spindle, and the spring Spring force is transferred through the spindle
to the needle This holds the needle on its seat and prevents fuel leaking from the end of the nozzle With the engine stopped, the injector holds fuel, but it is not under pressure.
figure 19.13 Sedimenter with water-level detector FORD figure 19.14 Combined fuel filter and sedimenter
DAIHATSU
Trang 10The simple injector works like this:
1 The fuel charge from the injection pump enters the
injector through the inlet connection It passes
down the drilled passage to the gallery in the nozzle
near the bottom of the injector.
2 When the gallery is pressurised with fuel, pressure
under the needle forces it upwards against the
spring, and the high-pressure fuel in the gallery is
sprayed into the combustion chamber.
3 When delivery from the injection pump ceases, the
pressure in the injector drops and the spring returns
the needle to its seat.
4 A small amount of fuel leaks up past the needle.
This lubricates and cools the injector before passing
out through the leak-off connection near the top of the injector.
The speed at which the pressure in the injector drops causes the needle to close rapidly This gives a sharp cut-off and prevents dribble The fuel has to be injected at high pressure and as a fine spray Any fuel that dribbles into the combustion chamber will not burn properly.
■ Dribble from a faulty needle and seat will cause soot and black smoke from the exhaust.
figure 19.15 Simplified diagram showing injector action
fuel inlet
figure 19.16 Sectional view of an injector
Trang 11Some injectors are threaded into the cylinder head,
others are clamped or bolted to the cylinder head.
Flanged injector
A flange-mounted injector is shown in Figure 19.18.
When installed in the cylinder head, it is secured by
two bolts This injector is the type used with direct
injection and mainly on larger engines It has a long
nozzle to reach through the cylinder head to the combustion chamber Figure 19.19 shows its internal construction.
figure 19.17 Dismantled parts of an injector TOYOTA
figure 19.18 Flanged-type injector
figure 19.19 Internal construction of a flanged-type
injector LUCAS/CAV
Injector nozzles
The function of an injector nozzle and its needle is to inject a spray of fuel into the combustion chamber in a form which will readily burn To achieve this, various types of nozzles have been designed These vary in length, number of holes and the angle of the holes The shape of the end of the needle can be flat, tapered or conical.
Some of the types of nozzles are shown in Figure 19.20 The fine holes in some injector nozzles are drilled mechanically In others, a process of electrical- discharge machining is used.
Single-hole nozzles
These nozzles have a single small hole drilled through the nozzle end The diameter of the hole can be from 0.2 mm upwards The conical-end single-hole nozzle has a single hole drilled at an angle to suit the particular engine design.
Multihole nozzles
These nozzles have two or more holes drilled in the end of the nozzle The number of holes and their size and position depend on the requirements of the engine.
Trang 12Long-stem nozzles
This type of nozzle has a long stem which is an
extension of the underside of the nozzle The end of
the stem carries the normal holes and valve seat The
long stem enables the part of the nozzle that has fine
clearances (between the needle and the nozzle) to be
kept away from the combustion chamber This enables
this part of the injector to operate in a comparatively
cooler area of the cylinder head.
Pintle nozzles
This type of nozzle has a much larger hole than other
types, and the end of the needle is formed into a pin or
pintle that protrudes through the hole By modifying
the shape and size of the pintle, injectors can produce
different spray patterns The spray can be varied from
a small hollow cone to a hollow cone with an angle of
60°.
Delay nozzles are a modified pintle-type in which
the shape of the pintle has been designed to reduce the
rate of injection at the beginning of the delivery This decreases the amount of fuel in the combustion chamber when combustion commences, and so reduces diesel knock.
■ Pintle nozzles are designed for use in engines with indirect injection, that is, those with an air cell, a swirl chamber or a precombustion chamber.
Sac-hole and seat-hole nozzles
Some nozzles have a small chamber under the tip of the needle into which the holes are drilled This is called a sac-hole and the nozzles are referred to as sac- hole nozzles Other nozzles have their holes drilled into the nozzle seat and are referred to as seat-hole nozzles These two designs are shown in Figure 19.21 With seat-hole nozzles, the taper on the needle tip covers the hole and so the needle is not exposed to the com- bustion gases.
figure 19.20 Types of injector nozzles LUCAS/CAV
figure 19.21 Injector nozzles
(a) sac-hole nozzle (b) seat-hole nozzle BOSCH
Electronically controlled injectors
The injectors used with common-rail injection systems have a solenoid that is electronically controlled These are different to other injectors which are hydraulically operated by fuel pressure.
■ Operation of these injectors is covered later under the section ‘Injectors for common-rail system’.
Trang 13Distributor injection pumps:
axial type
Figure 19.22 shows the external parts of a
distributor-type injection pump This design of pump is fitted to
the diesel engines of many passenger cars and light
commercial vehicles The pump is flange-mounted and
driven from the engine’s timing chain or timing belt It
rotates at camshaft speed.
Pump operation
To understand pump operation, it is necessary to consider both plunger motion and pumping action When the pump rotates, the cam disc and the plunger also rotate and the disc and the plunger are moved backwards and forwards by the action of the cams against the rollers The plunger therefore slides
in and out in its barrel and it also rotates.
The plunger has intake slits which cover and uncover the intake port as the plunger rotates It also has distribution slits that cover and uncover the distribution port as the plunger rotates.
The motion of the plunger performs three functions:
1 It opens and closes the fuel intake port to the pressure chamber, which is located at the end of the plunger.
2 It pressurises the fuel in the pressure chamber.
3 It distributes pressurised fuel to the correct injector
at the right time.
Functions 1 and 3 are performed by the rotary motion of the plunger opening and closing ports, while function 2 is performed by its sliding motion.
■ A fourth function, metering the quantity of fuel, is performed by the control sleeve.
Pumping action
The pumping section is shown in Figure 19.24 This is the part of the injection pump that pumps, meters and distributes high-pressure fuel to the injectors.
figure 19.22 External parts of a distributor-type injection
pump TOYOTA
figure 19.23 Schematic arrangement of the high-pressure
pumping section of an axial-type distributor pump ZEXEL
Operating parts of the pump
The main operating parts of the pump, excluding the
governor, are shown schematically in Figure 19.23.
These are:
1 A vane feed pump that supplies fuel at low pressure.
2 A cam disc that has one cam on its face for each
engine cylinder.
3 Rollers that the cam disc operates against.
4 A cam spring that holds the cam disc against the
rollers.
5 A plunger in a barrel that produces high fuel
pressure for injection.
6 Delivery valves that deliver the fuel to the injectors.
7 A control sleeve that controls the quantity of fuel
delivered to the injectors.
The cam disc is held against the rollers by the
spring The plunger is attached to the disc and they
both rotate together with the pump shaft.
Trang 14The pumping actions that occur are shown in the
diagrams in Figure 19.25 These are as follows:
1 Intake stroke When the intake slit comes in line
with the intake port, fuel from the feed pump will
flow into the pressure chamber and into the
drillings in the plunger body.
2 Injection stroke During the injection stroke, the
plunger will be pushed down its barrel The intake
port will have closed and the fuel will be
compressed.
As the plunger rotates, the distributing slit in the
plunger will come into line with the distribution
port Pressurised fuel will raise the delivery valve
and deliver fuel through the injector pipe to the
injector (as shown in the illustration).
3 End of delivery As the plunger slides to the right,
the cut-off port in the plunger will become exposed,
and pressurised fuel will spill from the cut-off port.
This reduces pressure, and the delivery valve will
close to end delivery.
Controlling the quantity of fuel
The quantity of fuel injected is metered by the control
sleeve, which determines the end of delivery If the
sleeve is moved to the left, the quantity of fuel will
decrease – if the sleeve is moved to the right, the
quantity of fuel will increase.
Sliding the sleeve along the plunger alters the tive length of the plunger stroke When the sleeve is moved to the left, the cut-off port is exposed earlier, and when the sleeve is moved to the right, the cut-off port is exposed later.
effec-■ The start of delivery remains the same, but the point where pumping ceases is altered to suit the quantity of fuel to be injected.
Delivery valve action
The delivery valves that are located in the distributor head of the pump play an important part in injector operation The valve is lifted off its seat by the pressure of fuel from the plunger during delivery When pumping ceases, it is forced back onto its seat
by the spring.
The valve has a small piston that moves down its bore as the valve closes This reduces the volume in the delivery valve assembly so that the pressure in the injector pipe drops rapidly This allows the needle in the injector to snap shut and give a clean cut-off of the fuel spray.
Timing advance
The arrangement for automatically advancing the injection is shown in Figure 19.26 The roller assembly that operates the cam disc is rotated a few degrees in a direction opposite to pump rotation This causes the plunger action to commence earlier, and so injection timing is advanced.
The movement of the roller assembly is controlled
by a piston in a cylinder which is subject to feed pump pressure As the speed of the injection pump increases, feed pump pressure also increases to move the piston against the spring This turns the roller assembly to advance injection.
Stopping the engine
The fuel cut-off solenoid is used to stop the engine It does this by closing off the fuel passage to the intake port (refer to Figure 19.25).
When the engine is switched on, the solenoid is energised and its plunger is raised This opens the fuel intake port so that fuel from the feed pump can reach the plunger.
When the engine is switched off, the solenoid is energised and the plunger is pushed down by its spring
de-to close off the intake port and block the supply of fuel This stops the engine.
figure 19.24 Pumping section of an axial distributor pump
ZEXEL
Trang 15Governor for axial pumps
Figure 19.27 is a schematic arrangement of the
mechanical governor for an axial-type distributor
pump The actual governor has three levers, but these
have been simplified and shown as a single lever.
The main parts of the governor and control are as
follows:
1 Control lever – connected externally to the driver’s
accelerator and internally to the governor spring.
2 Governor spring – holds the lever against the governor sleeve Spring tension is altered by movement of the control lever, which is moved by the accelerator.
3 Flyweights – rotated by the governor shaft and thrown outwards by centrifugal force.
4 Governor sleeve – moved against the lever by the action of the flyweights.
figure 19.25 Action of the plunger of an axial-type distributor pump ZEXEL
Trang 165 Lever – pivots on the pivot pin It has the governor
spring at the top and a ball that fits into the control
sleeve at the bottom.
6 Control sleeve – slides on the plunger to vary the amount of fuel injected.
Governor operation
The governor shaft and flyweights are driven by gears from the pump shaft so that they rotate at a higher than pump speed When the flyweights are rotated, their ends are moved outwards by centrifugal force This outward movement is related to rotational speed – the faster the flyweights rotate, the further out they move Movement
of the flyweights is transferred to the governor linkage and used to control the engine speed and power.
Referring to Figure 19.27, outward movement of the flyweights will move the governor sleeve along its shaft to push against the lever Lever movement will then slide the control sleeve on the pump plunger to vary the quantity of fuel injected This will control the speed of the engine.
The governor spring opposes flyweight movement When the tension of the spring is reduced, the fly- weights are allowed to move outwards to increase engine speed When the tension of the spring is increased, the flyweights are allowed less movement The position of the flyweights is therefore a balance between centrifugal force and spring force.
figure 19.26 Timing device used on an axial distributor
pump ZEXEL
figure 19.27 Governor arrangement for an axial distributor pump