fuel injection pump

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D ESEL ENGINEFUNDAMENTALS

D ESELD I E S E L E N G I N E S & F U E L S Y S T E M S E - T E X T

Overview

Fuel supply systems

In-line pump

Rotary pump

Common rail

Unit injection

Fuel supply pumps

Plunger pump

Diaphragm pump

Gear pump

Roller cell

Fuel filters

Filtering material

Types of filters

Fuel pipes

Water separators

Filter service

Injector filters

Revision questions

4 MECHANICAL FUEL INJECTIONSYSTEMS4.1 FUEL SUPPLY SYSTEMS


D ESELMECHANICAL FUEL INJECTION SYSTEMS

D I E S E L E N G I N E S & F U E L S Y S T E M S E - T E X T

SECTION CONTENTS

2011 DEFS 4.1 FUEL SUPPLY SYSTEMS 3

MODULE CONTENTS

Common Rai l Fuel System

A general fuel system layout of a common rail fuel system is shown in Fig 3. In a common rail system an electric or gear pump is used to supply fuel to the high pressure pump. Electric supply pumps are mainly used on cars and the gear pump is used on all other commercial applications.

The electric fuel supply pump is located inside the fuel tank and operates as soon as the ignition switch is turned on. This ensures fast engine starting as the low pressure fuel circuit is charged prior to engine being started.

The gear supply pump on the other hand is flanged to the back of the high pressure common rail pump and is driven by its input shaft. Both fuel supply pumps draw fuel via a pre filter in the fuel tank then pump the fuel through the fuel filter before delivering it to the high pressure pump. Fuel bypassed from the fuel rail helps to supplement the fuel flow in the low pressure circuit and leak off fuel from within the high pressure pump returns to the fuel tank.

Fig 2. Schematic diagram of a distributor pump fuel injection systemCourtesy of Bosch

Fig 3. Schematic diagram of a common rail fuel injection system. Courtesy of MAN Nutzfahrzeuge




SECTION CONTENTS

2011 DEFS 4.1 FUEL SUPPLY SYSTEMS 5

MODULE CONTENTS

Fuel tank

Common rail fuel pump

Fuel filter Fuel rail (common rail)

Injector

High pressure fuel line

Fuel supply pump

Fuel tank

Distributorpump

Injector

Fuel filterGlow plug

Fuel return line

Return line




SECTION CONTENTS

2011 DEFS 4.2 INJECTORS 15

MODULE CONTENTS

44.2 INJECTORS

Overview

Injector operation

Injector nozzles

Multi hole nozzles

Pintle nozzles

Mechanical unit injector operation

Electronic unit injector operation

Common rail injector

Injector service (conventional)

Injector service (common rail)

Injector testing

Isolating a faulty injector

Revision questions

Industry updates

Related web sites

Additional diagrams/photos

MECHANICAL FUEL INJECTION SYSTEMS

The injector section consists of a nozzle body and needle valve assembly. The operation of the nozzle assembly is identical to that of a conventional injector in that fuel pressure acts on the needle valve shoulder lifting the needle valve off its seat allowing fuel to pass through the multi spray holes and atomise into the combustion chamber.

Injector operation is described under the following headings:

No injection

Start of injection

End of injection

No injection

With the solenoid coil not energised, the solenoid valve spring presses the valve body and valve ball onto the ball seat of the orifice plate closing off fuel flow through the orifice plate. Inside the control chamber the pressure rises to that of the fuel rail. The same pressure is also applied to the nozzle needle shoulder. The fuel pressure now acting on the nozzle needle shoulder cannot overcome the combined forces of the fuel pressure acting on top of the command piston and the nozzle spring. Therefore, the nozzle needle stays seated on the nozzle seat as shown in Fig 12.

Start of injection

When the solenoid coil is energised by the electronic control module, the electromagnetic force draws the valve body upward allowing the ball seat to open. Fuel in the control chamber now passes through the orifice plate and flows to the fuel tank. With the pressure of the fuel in the control chamber now reduced, the fuel pressure acting on the underside of the nozzle needle shoulder is great enough to lift the nozzle needle off it seat. Fuel under pressure now flows through the nozzle spray holes and is atomised as it enters into the combustion chamber as shown in Fig 13. Note: As fuel flow into and out of the control chamber is controlled by inlet and outlet restricting orifii, rail pressure is not noticeably reduced during injection by the small quantity of fuel returning to the fuel tank.

The engine control unit determines the length of the injection period by energising the injectors electrical solenoid coil for the pre-injection, main and possibly post-injection periods. In order to achieve multiple injections during the power stroke, some injectors are using a second solenoid coil to assist in the rapid opening and closing of the nozzle needle.

Fig 12. Schematic diagram of a common rail injector showing no injection

Courtesy of Mitsubishi Heavy Industries Ltd

Fig 13. Schematic diagram of a common rail injector showing start of injection

Courtesy of Mitsubishi Heavy Industries Ltd




SECTION CONTENTS

2011 DEFS 4.2 INJECTORS 21

MODULE CONTENTS

Solenoid coil

Valve body

Orifice plate

Control chamber

Nozzle needle

Nozzle spring

Command piston

Fuel - (from common rail)

Ball valve & seat

Solenoid valve spring

Valve body

Spring Solenoid coil

Nozzle needle

Nozzle spring

Command piston

Fuel - (from common rail)

Fuel - (to fueltank)

Ball valve(open)

Reduced pressure in control chamber




SECTION CONTENTS

2011 DEFS 4.3 FLANGE & IN-LINE INJECTION PUMPS 31

MODULE CONTENTS

MECHANICAL FUEL INJECTION SYSTEMS44.3 FLANGE & IN-LINE INJECTION PUMPS

Overview

Function of injection pump

Flange mounted injection pumps

Construction

Pumping principle

Plunger and helix

Delivery valve function

In-line injection pump

Construction

Camshaft design

Pump lubrication

Automatic advance unit

Pump servicing

Pump to engine timing

Mark method

Spill time method

Advanced and retarted timing

Revision questions

Industry updates

Related web sites

Delivery of fuel ceases when the plunger helix passes the barrel spill port (or control port), and the delivery valve returns to its seat. During the remainder of the stroke, the fuel displaced by the plunger simply returns to the gallery via the vertical slot, cut away area and spill port. Thus fuel ceases to be injected when the helix uncovers the spill port.

Metering the fuel chargeSince the plunger is cam driven, its stroke is constant and cannot be varied to control the quantity of fuel injected per stroke. However, the effective part of the pumping stroke can be

varied to control the quantity of fuel injected per stroke simply by rotating the plunger in the barrel.

Fuel delivery begins at the instant the top of the plunger covers the barrel ports and continues until the helix edge uncovers the spill port, at which point fuel trapped above the plunger is allowed to return to the fuel gallery.

Thus the effective pumping stroke ceases when the spill port is uncovered, and is directly controlled by the distance through which the plunger must travel before the edge of the helix passes the bottom of the spill port.

Fig 5. Charging and delivery cycle (maximum fuel position)Courtesy of Bosch

Fig 6. Control of fuel deliveryCourtesy of Bosch




SECTION CONTENTS

2011 DEFS 4.3 FLANGE & IN-LINE INJECTION PUMPS 35

MODULE CONTENTS

Charging cycle Port closing(start of delivery)

Delivery Spill port opening(end of delivery)

Plunger helix

Inlet port Spill

port

No delivery Partial delivery Maximum delivery

Inlet port

Spill port

Plunger helix




SECTION CONTENTS

2011 DEFS 4.4 DISTRIBUTOR TYPE INJECTION PUMP 44

MODULE CONTENTS

MECHANICAL FUEL INJECTION SYSTEMS44.4 DISTRIBUTOR TYPE

INJECTION PUMP

Overview

VE Pump

Construction and operation

Fuel supply pump

Pumping and fuel distribution

Fuel metering

Delivery valve

Mechanical governor

Variable speed

Solenoid shut off valve

Automatic advance unit

Air-fuel ratio control

Pump timing

Revision questions

Industry updates

Related web sites

Additional diagrams/photos

Fuel Supply PumpLow pressure charging of the pump housing is accomplished, by a vane type fuel supply pump situated at the drive end of the distributor pump. Fuel flow is from the fuel tank through the fuel filter and into the vane pump, from here it enters the pump housing at pressures that vary between 360 kPa and 810 kPa. Generally there is no fuel feed pump fitted to this fuel system, as the vane pump serves this purpose.

Being a constant displacement pump, the fuel supply pump can deliver several times the amount of fuel required for injection.

Therefore, when the pump housing pressure reaches a predetermined level, excess fuel delivery is relieved via a pressure control valve and returned back to the inlet side of the fuel supply pump, as shown in Fig 3.

The pressure control valve is located beside the fuel supply pump and is of the spring loaded piston type. This valve is pre-set on manufacture and requires no further adjustment.

For the purpose of self bleeding and cooling of the entire pump, fuel circulates through an overflow restricting orifice back to the fuel tank. The overflow restricting orifice is 0.6 mm in diameter and is situated in the banjo bolt in the fuel return line on top of the pump housing as shown in Fig 2. While this orifice allows fuel to return to the fuel tank, it offers sufficient restriction to fuel flow from the fuel supply pump to cause the injection pump housing to be pressurised. Further, in conjunction with the fuel supply pump pressure control valve, the orifice is responsible for the pump housing fuel pressure necessary for the charging of the high pressure chamber and the operation of the automatic injection advance unit.

Fig 2. Cut away section of a VE fuel injection pump Courtesy of Bosch

Fig 3. Schematic diagram of the operation of a vane type fuel supply pump




SECTION CONTENTS

2011 DEFS 4.4 DISTRIBUTOR TYPE INJECTION PUMP 46

MODULE CONTENTS

Cam plate

Solenoid shut off valve

Governor assembly

Overflow restriction orifice

Distributor head with high pressure pump

Automatic advanceunit

Pressure controlvalve

Fuel supplypump

Maximum fuel adjust screw

Fuel from tank

Pressure control valve piston

Drive shaft

Vane

Rotor

To pump housing




SECTION CONTENTS

2011 DEFS 4.5 GOVERNORS 57

MODULE CONTENTS

MECHANICAL FUEL INJECTION SYSTEMS44.5 GOVERNORS

Overview

Function of a governor

Classification of governors

Types of governors

Governor terminology

Graphs of governor control and engine fuelling

Mechanical governors

Constant speed

Variable speed

Idle maximum speed

Pneumatic governor

Electronic governor

Revision questions

Simple Constant Speed Governor

Constant speed governors are fitted to engines that are required to run at a set or constant speed, and are governed to this set speed.

Applications include engines that power alternator sets, water pumps, conveyors, etc.

The simple constant speed governor as shown in Figs 4 consists of two pivoted flyweights, fixed to a pivot plate, which rotates with the pump camshaft, a sliding control sleeve, a pivoted fork and a governor spring. Spring force acts against the sleeve, forcing it against the lever arm of the flyweights, which are forced in towards the shaft.

As the shaft rotates, centrifugal force causes the flyweights to move outwards from the shaft, the lever arm thrusting against the sleeve. Thus the sleeve is balanced between spring force on the one end and the force exerted by the flyweights on the other.

The governor mechanism connects to the pump rack via the pivoted fork, one end of which engages in a groove in the sleeve with the other end connecting to the rack via a link.

Should the engine speed drop due to an increase in engine load, the centrifugal force acting on the weights will decrease, allowing the spring to push the sleeve along the shaft. This movement will move the rack, via the pivoted fork, to increase the fuel supply to the engine.

On the other hand, should the engine speed increase due to a lightening of the load, the subsequent increase in centrifugal force will fling the flyweights outwards and the lever arms will force the sleeve along the shaft against the spring. Movement in this direction will move the rack to reduce the fuel delivery from the pump.

Thus any change in the engine speed will cause an immediate change in the quantity of fuel injected, which will compensate for the speed change.

Simple Variable Speed Governor

In applications where engines may be required to operate at any selected speed, variable speed governors are used. These governors govern the engine at any set engine speed, from idle to maximum. Governors of this type are used extensively in engines for earthmoving equipment and farm tractors.

Fig 3. Mechanical governor with centrifugal weights Courtesy of Bosch

Fig 4. A simple constant speed governor




SECTION CONTENTS

2011 DEFS 4.5 GOVERNORS 61

MODULE CONTENTS

Centrifugal weights

Control rack

Governorspring

Control lever

Fuel control rack

Maximum fuel rack stop screw

Pumping element

Fulcrum lever

Governor spring

Centrifugal weights

Sliding sleeve

Fixed throttleposition

fuel injection pump

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