tdi-tech.pdf

1,9 ltr-TDI-Industrial Engine

Technical Status: 4/1999

Contents

· Combustion process . . . . . . . . . . . . . . . .3

· Injectors . . . . . . . . . . . . . . . . . . . . . . . . .4

· Needle Lift Sender . . . . . . . . . . . . . . . . .5

· Air-mass Flow Meter . . . . . . . . . . . . . . .6

· Modulating piston movement sender . .7

· Installation position . . . . . . . . . . . . . . . .8

· System overview . . . . . . . . . . . . . . . . .10

· Fuel regulation . . . . . . . . . . . . . . . . . . .12

· Injection commencement control . . . . .17

· Exhaust gas recirculation . . . . . . . . . . .22

· Charge pressure control . . . . . . . . . . .24

· Glow plug system . . . . . . . . . . . . . . . .26

· Emission characteristics . . . . . . . . . . . .27

· Internal functions in the control unit . .29

· Self-diagnosis . . . . . . . . . . . . . . . . . . .30

· Performance diagram . . . . . . . . . . . . .31

· Specifications . . . . . . . . . . . . . . . . . . . .32

Detailed instructions regarding testing, adjustment and repair can be found in

the Workshop Manual "Volkswagen Industrial Engine".

Combustion process

In the direct injection engine, diesel fuel is injected directly into the main combustion

chamber. This results in more efficient combustion and lower consumption.

The intake port, pistons and injectors have been designed specifically to optimise

the combustion process with respect to noise emission and running characteristics.

Inlet swirl port

The intake port is shaped in such a way that it

induces a swirling movement of the intake air

and, as a result, produces greater turbulence

in the combustion chamber and piston recess.

Piston recess

The shape of the piston recess has been opti-

mised specially for this engine.

5-hole injector

The fuel is injected into the piston recess in

two stages and is ignited by the hot air.

The two-stage injection process avoids a sharp

pressure rise.

Injector needle

Two-spring injector holder

To minimise the combustion noise level in the diesel engine and keep mechanical

load low, it is necessary for the pressure to rise gently in the combustion chamber.

In the case of chamber-type diesel engines, this gentle rise in pressure is achieved,

first, by injecting fuel into the pre-chamber or the swirl chamber and, secondly, by

using pintle-type injectors. Also, the fuel should be injected gradually, not all at once.

A two-spring injector holder has been developed for the 1.9-ltr. direct injection

engine. This injector holder, a key factor contributing to the engine's "soft" combus-

tion characteristic, allows fuel to be injected in two stages.

The injector is designed as a five-hole nozzle.

Stroke 1

Stroke 1+2

Function

Spring 1

Two springs with different

thicknesses are integrated

in the injector holder.

The springs have been

adapted in such a way

that the injector needle is

only lifted against the

force of the first spring

when injection starts.

A small quantity of fuel is

pre-injected through the

small gap which appears

at low pressure.

Stroke 2

Spring 2

This pre-injection cycle produces a gentle rise in the combustion pressure

and creates the conditions for igniting the main fuel quantity.

Injector needle

As the injection pump delivers more fuel than can actually flow through

the small gap, the pressure in the injector rises. The force of the second

spring is overcome, and the injector needle is lifted further. The main

injection cycle now follows at a higher injection pressure.

Needle Lift Sender

The injector of the 3rd cylinder is equipped with a needle lift sender (G80) for regis-

tering the point of commencement of injection.

The sender signals the actual opening time of the injector to the control unit. This

signal provides the control unit with feedback on whether the point of commence-

ment of fuel injection conforms to the map.

Injector holder

Solenoid

Function

Needle lift sender G80 is a

solenoid and is supplied with a

constant current by the control

unit. This produces a magnetic

field.

A pressure pin inside the sole-

noid forms an extension to the

end of the injector needle. The

movement of the injector nee-

dle alters the magnetic field

and causes distortion of the

DC voltage applied to the sole-

noid.

Pressure pin

The control unit calculates the

actual point of commencement

of fuel injection from the time

difference between the needle

lift pulse and the TDC signal

supplied by the engine speed

sender. At the same time, the

system compares the actual

point of commencement of

injection with the setpoint

stored in the control unit and

corrects any deviations from

the setpoint.

Substitute function

If the needle lift sender fails, an emergency running program is started. In this pro-

gram, the commencement of fuel injection is controlled according to fixed setpoints

as defined in a map. The injection quantity reduced in addition.

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