Pt fuel system

PT fuel system is made from the fuel tank, float tank, filter, governor, PT fuel pump, injector and low- pressure pipeline and return pipe. When working, PT fuel pump is responsible for oil regulator, PT injector completes the tasks that generate high pressure and timing injection.

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PT FUEL SYSTEM








FOREWORD
This manual gives an explanation of the structure and function of the PT fuel system
used in Cummins original engines mounted in construction machines manufactured by
Komatsu Ltd.
Use this manual for class room lectures on the structure and function of the PT fuel
system for training courses for fuel system specialists. Also, if a senior mechanic reads this
manual he will gain knowledge about the structure and function of the PT fuel system.
This will assist him in his daily trouble shooting and he will understand better service
news and other materials concerned with technical information included in this manual.

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CONTENTS

1. FUEL SYSTEM IN CUMMINS ENGINE……………… …………………………..…3

2. INJECTORS…………………………… …………………………………… …....……..7

2.1 General .................................................................................................................7
2.2 Metering Action by Flange Type Injector ........................................................ ..8
2.3 Fuel Flow through Injector .............................................................................. .10
2.4 Care of the Injector ........................................................................................... 12
2.5 Plunger Movement ........................................................................................... 14
2.6 Injector Removal and Installation .................................................................... 18
2.7 Cylindrical PT (Type D) Injector ..................................................................... 20

3.PT PUMP .........................................................................................................................27

3.1 General ............................................................................................................. 27
3.2 Construction of the PT Pump ........................................................................... 28
3.3 PTG Governor .................................................................................................. 30
3.4 Throttle ..............................................................................................................35
3.5 MVS Governor ..................................................................................................36
3.6 Shutoff Valve .................................................................................................... 39
3.7 Integral Type PT (Type G) Fuel Pump Cooling Feature .................................. 40
3.8 Aneroid Control Valve ...................................................................................... 41
3.9 AFC Control ...................................................................................................... 46
3.10PTG-VS Governor ............................................................................................48
3.11 Fuel Flow of PTG-VS Fuel Pump with AFC .................................................. 50

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2.7 Cylindrical PT (type D) Injector

The injectors used with the PT fuel system are grouped into two basis groups,
cylindrical in shape without a flange or flange type. The details of the flange type have been
covered in the preceding paragraphs. Cylindrical injectors are used in engines with the
cylinder head with internal fuel drillings. Cylindrical PT (type D) will be described in details
following the brief description of cylindrical injectors of other types.

• Cylindrical PT Injector

A limited number of engines with internal
fuel drillings in the cylinder head used this
type. An adjustable orifice plug was
contained in the inlet passage.

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Cylindrical PT (type B) Injector

A ball valve (10) (Fig. 2-27) is
included to aid in the control of fuel
flow and the adjustable orifice plug is
burnished to size during testing.





















This type has the same features as the
PT (type B) injector, plus a two-piece
cup consisting of a cup (1) and cup
retainer (16) (Fig. 2-28).

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 PT (type D) Injector


The PT (type D) is a refinement of the PT (type B and C) cylindrical injectors. The
changes in parts design of PT (type D) provides more parts interchangeability, and the areas
of the parts subject to wear are localized in smaller parts for easier servicing.
While former injectors have a body with the moving part or plunger running the full
length, the PT (type D) has a short barrel and plunger to provide the same function. The
shorter barrel plunger bore made it possible to use materials of greater wear resistance and
result in smaller replacement assembly.
The barrel and plunger assembly is made up of a coupling (3), plunger (11) and barrel (12).
The coupling (3) and plunger (11) are swaged assembly.
Plunger and barrel kit part number--- AR-40G63 (Cummins Parts No.), CUAR-40063
(Komatsu Part No.)--- is available as follows;

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Injector parts-flange type and PT (type B and C)
 Adjustable orifice plug
Orifice plug used in inlet drilling of flanged injectors and cylindrical injectors to
adjust fuel delivery. Fuel delivery is adjusted by changing the orifice plug or by
burnishing the plug in operating position, see injector description. Some orifice plugs
have a flange and required a gasket beneath the flange.
 Drain Orifice
The drilled orifice in cup end of the injector is the drain drilling. This orifice is fixed
in size and must not be altered in any way.
 Metering Orifice
The orifice in cup end of the injector allowing fuel to enter injector plunger bore and
cup. This orifice is fixed in size and must not be altered in any way.
 Cup Gasket
When PT fuel system injectors are fitted with oversize plungers, thicker cup gaskets
must be used to provide the original relationship between the plunger and metering
orifice. PT (type C) injectors do not use a cup gasket.

Injector parts-PT (type D)
 Adapter
 In Fig. 2-29, the adapter (2) houses the plunger return spring (1), adjustable orifice
(5), orifice gasket (4), fuel screen (6) and screen retainer (7) and carries the "O" ring
seals (8) on the outside which seal against the head to form fuel inlet and drain
passages. Fuel enters through orifice (5) and flows to barrel (12), pass check ball (10)
to the cup-to-barrel passage up to the metering orifice where it is metered into the cup
(14). Fuel not used circulates past the metering orifice, around the plunger and out the
drain passage while the plunger is seated in the cup. The cup, adapter and barrel are
held in assembled position by the cup retainer (13).

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 Metering Orifice of PT (type D) Injector
The metering orifice near the cup end of the barrel is of fixed size and must not be
altered in any way; barrels differ for engine model in relation to the size of the
metering orifice as governed by engine fuel requirements.

PT (type D) is found in three forms. These being identified by the plunger diameters and
found on the following engine models

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Upstroke Start (Fuel Circulates)
Fuel at low pressure enters the injector through
screen (A) and flows through inlet orifice (B), internal
drillings and drain passage (D) and to the fuel tank.
The amount of fuel flowing through the injector
is determined by the fuel pressure at the inlet orifice
and the inlet orifice diameter. Fuel pressure is also
determined by engine speed, governor and throttle.













Upstroke Complete (Fuel Enters Injector Cup)
As the injector plunger moves upward, the metering
orifice is uncovered and fuel enters the injector cup. The
amount is determined by the fuel pressure. The drain
passage is blocked momentarily, stopping circulation of fuel
and isolating the metering orifice from pressure pulsations.

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Down stroke (fuel injection)
As the plunger moves down and
closes the metering orifice, fuel entry into
the cup is cut off. As the plunger continues
down, it forces fuel out of the cup through
tiny holes at high pressure as a fine spray.
This assures complete combustion of fuel in
the cylinder. When the drain passage is
uncovered by the plunger undercut, fuel
again begins to flow through the return
passage to the fuel tank.













Down stroke complete
After injection is complete the plunger remains
seated until the next metering and injection cycle. No
fuel is reaching the injector cup. However, it does
flow freely through the injector and returns to the
fuel tank.

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3.7 Integral Type PT (type G) Fuel Pump Cooling Feature


Fuel pumps have been revised to incorporate a new fuel pump cooling feature as an
integral part of the gear pump.
The small amount of fuel which this new cooling device routes back to the fuel tank,
previously was recirculated internally. Therefore, this method of cooling does not use any of
the normal delivery of the gear pump and present fuel pump calibration specifications will
still apply.
This bleed fuel is that fuel which flows through and lubricates gear pump bearing
bores. Previously, this fuel was dumped back into the suction side of the gear pump. With the
integral bleed gear pump, the lubricating fuel flow through three gear pump bearings is bled
off through an external tapped drain hole. The former internal pump drillings which permitted
this fuel to return to the suction side, have been eliminated.
The inboard main shaft bearing bore still returns its fuel to the gear pump suction. The
inboard idler shaft bearing fuel flows through the hollow idler shaft to the external drain line.
As can be seen from the sketch both outboard gear pump bearings drain externally.
Since three of the bearing bores drain externally, it is apparent that both tapped holes
in the gear pump housing cannot be plugged. Plugging both tapped openings will prevent
lubricating and cooling fuel flow through the three bearing bores and gear pump seizure will
occur.
Both ends of the through drain drilling are tapped so that gear pumps can be
converted from R.H. to L.H. in the normal manner.
Under no circumstances should the pump be operated with the cooling return flow
plugged. This fuel flow is necessary to lubricate the bearing surfaces within the gear pump.
It has to be noted that the spring loaded check valve is included in the elbow fitting at
the outlet of the gear pump to prevent the reverse flow.

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3.8 Aneroid Control Valve





When an engine is running at low speeds, and an accelerator pedal is depressed
quickly, intake air does not increase in volume appropriate to increased fuel. Since the fuel
control system is connected mechanically by linkage, fuel supply can be increased almost
simultaneously. On the other hand, air intake increases only after engine speed rises.
In order to prevent black smoke, which easily arises from a lack of air, the aneroid
control valve controls fuel supply so that only fuel appropriate to air volume supplied to the
engine is injected.

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Structure and function





Fuel flow is as in drawing above. A part of the fuel under the pressure from the PT pump
goes to the aneroid control valve to make by-pass circuit.

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 Starting;
When the engine is started with a starting motor, volume of fuel supplied by the PT
pump is small and its pressure also is low. Consequently the stop valve for starting
remains closed, fuel is not by-passed and starting is made easy.




 Idling;



Once the engine starts fuel pressure overcomes the force of the spring of the stop valve for
starting, pushes the valve up, and some of the fuel flows into the valve (throttle shaft).

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When running at low speed, the valve is fully open because air intake manifold
pressure is low, and fuel passes through the notches and is by-passed to the float tank.
 Rapid Acceleration

When engine speed is increased rapidly (when accelerator pedal is depressed suddenly)
the turbocharger speed cannot be increased fast enough, and air intake manifold pressure is
low. Therefore, the valve is open and fuel is by-passing.
As air intake manifold pressure rises and becomes greater than the bellows spring force,
the bellows are pushed up, the valve (throttle shaft) is rotated by a lever and the notch begins
to close. Until before the notch is fully closed, the fuel continues to by-pass through the valve
that the fuel pressure to the injection is low not to cause the black smoking.

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 Normal Driving
During normal running when engine speed increases (turbocharger revolutions also increase)
and air intake manifold pressure is greater than the set pressure of the bellows spring, the
notch of the valve (throttle shaft) is shut. Therefore, since fuel cannot by-pass, the engine
gives the same performance (output) as an engine without an aneroid control valve.






The graph on the left indicates torque to engine
RPM relationship of a particular cummins engine. It
shows that this engine performs in the same manner
as the engine without a turbocharger at RPMS
higher than that shown by (2).







(1): Point where notch begins to close (air intake manifold pressure ………100 - 130mmHg)
(2): Point where notch has finished closing (air intake manifold pressure ……….355mmHg)

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3.9 AFC Control






The new model PT (type G) AFC fuel pump has been newly designed as an alternate
to the PT (type G) fuel pomp plus aneroid combination for engines with turbocharger. It
basically differs from the aneroid valve which by-passes fuel pressure in on or off manner. Its
function is to control the air to fuel mixture rate by limiting fuel pressure and fuel flow so that
during engine acceleration period air and fuel mixture rate are in the correct proportion.
There is a particular plug to be installed in the housing of fuel pumps for engines
which do not require an air/fuel mixture control. All engines have this housing as a standard.

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Functional Principle








The difference between the PT (type G) and PT (type G) AFC fuel pumps is in the
line between the fuel pump throttle shaft and fuel shutoff valve. Fuel flows from the throttle
shaft directly to the fuel shut-off valve in the PT (type G) fuel pump.
In the PT (type G) AFC fuel pump, fuel leaving the throttle shaft passes through the
AFC unit to the fuel shut-off valve. (See above left figure).
Above right figure shows the fuel flow when the AFC control plunger is in "NO-AIR"
position. It shows the condition when an engine (with turbocharger) starts and its speed are
low so intake manifold pressure is too low to overcome AFC spring force. Fuel flows from
the throttle shaft along the "NO- AIR" needle valve passage. The needle valve acts to check
pressure and flow. The AFC plunger blocks the passage of fuel flow through the AFC barrel

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3.10 PTG-VS Governor



























Comparing the arrangement of the PTG-VS governor and the PTG-MVS governor



The VS governor has been designed to supplement the current PT (type G) standard
automotive governor. This pump plays a role of PT (type G) MVS.
This pump regulates speed over the total engine speed range without surging. With
PTG-VS governor engine speed droop rate is less than that with all previous pumps as shown
in Fig. 3-38.
Also, when compared with MVS governor its stability and response is superior.
(Movement of the VS governor plunger is smooth because it rotates.)

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The governor spring of the VS governor assembly is balanced with thrust of the
centrifugal force due to the revolution of the VS governor weight. The PTG-MVS governor
spring is balanced by the oil pressure of oil discharged from the gear pump.
The pressure regulator valve (as shown in Fig. 3-36) is for the purpose of pressurizing
inside the PTG-VS governor housing assembly.
The VS governor assembly is located above the fuel pump housing and front cover.
The VS governor weight is inside the upper front cover, and is gear-driven by the fuel pump
main shaft via an idler gear assembly. PT (type G) governor is located inside the bottom of
the housing as previously.
Since engine acceleration performance is very closely related to the adjustment of the
aneroid control valve, the bellows spring and shims, which control opening of the valve
(throttle shaft), under various engine running conditions are specified to the engines
respectively and are adjusted precisely with much attention.

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3.11 Fuel Flow of PTG-VS Fuel Pump with AFC
The following schematics show how the fuel flow situations vary with PTG-VS fuel
pump with AFC which was covered previously, depending on the running conditions.

Engine stopped
Solenoid valve is closed with ignition switch open. Turbo boost pressure is not
available to act upon diaphragm to defect AFC spring. AFC plunger is in the closed position.

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Starting and idling





With the ignition switch closed and solenoid valve caused to open, the fuel needed for
idling at low speeds flows through the stricted "NO-AIR" needle valve, VS governor and
solenoid valve (shut-off valve). The AFC plunger blocks fuel from passing through the AFC
barrel due to insufficient turbo "boost" pressure available to act upon the diaphragm to deflect
the AFC spring.

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Normal driving



Operator controls fuel flow and rail pressure to the injectors by a throttle pedal or
lever. The position of VS governor plunger controls the fuel flow and the rail pressure. VS
governor weight force and the counter acting forces by the VS governor spring force
determine the position of the VS governor plunger.
The governor weight force increases as speed increases. The amount of fuel delivered
to the VS governor depends upon the regulating counteracting forces of the governor spring
and torque spring which influences the amount of fuel by-passed at the end of the governor
plunger and idle spring plunger.
The maximum fuel pressure and fuel flow are regulated in the speed range of the
engine by the governor itself. Fuel is passing through the needle valve and AFC barrel since
sufficient turbo "boost" is available to act upon the diaphragm and overcome the AFC spring.
The final fuel flow is regulated at the VS governor and passes through the solenoid valve on
to the injector.

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Beginning of high speed governing






Fuel is flowing from PTG governor through both the needle valve and AFC barrel to
the VS governor. However, it can be noticed that the VS governor port is being closed which
causes more fuel to be by-passed by the governor plunger (5) and idle spring plunger (11), in
Fig. 3-39. The VS plunger and port thereby control governor regulation on the droop curve
by restricting fuel flow.

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Complete high speed governing



The fuel flow provided by the gear pump is restricted by VS governor. The supplied
fuel is being by-passed by the governor plunger (5) and idle spring plunger (11) and dump
ports (18), in Fig. 3-39, thus the fuel sufficient to maintain only high idle speed passes
through restricted "NO AIR" needle to the VS governor. AFC plunger blocks fuel from
passing through AFC barrel. Turbo boost pressure is not available to act upon diaphragm to
deflect AFC spring.

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