The 2.8 l Diesel engine in the LT ’97
Design and Function

In the LT ‘97 commercial vehicle series, Volkswagen is adding a high-performance 2.8 l engine with direct fuel injection to the
Diesel engine line.
In this self study programme we present the new designs and functions of individual systems of the new Diesel engine.

At a glance
Technical data .............................................................
Overview
4
Engine - mechanical ..................................................
Cylinder block
Oil circuit
Two-part flywheel
Timing gears
Direct injection
6
Diesel direct injection .................................................
14
General overview
Fuel supply
Distributor injection pump
Injection
Fuel cut-off
Speed control
Timing device
Injectors
Boost-pressure enrichment
Fuel filter
Turbocharger
Glow plug system ...................................................... 28
Self check .....................................................................
30
The Self Study Programme is not a repair manual!
For information on testing, adjustments and repairs, refer to the appropriate customer service literature.
New!
Important!
Note!
3

4
Technical Data
Engine data
Engine code:
Design:
Displacement:
Bore:
Stroke:
Compression ratio:
Rated output:
Maximum torque:
Mixture preparation:
AGK
4-cylinder in-line turbodiesel engine
2798 cm
3
93 mm dia.
103 mm
19 : 1
92 kW (125 HP) at 3500 rpm
280 Nm at
2200 rpm
Direct injection with mechanically controlled distributor injection pump
Oil cooler integrated in crankcase
Vibration damper for ribbed V-belt
100
90 300
80
70
60
50
40
30
1000 1500 2000 2500 3000 3500 4000 n (1/min)
197/1
275
250
225
200
Turbocharger
Oil filter
Tensioner for ribbed V-belt
Vibration damper
2 coolant thermostat valves
197/20

Overview
The 2.8 l turbodiesel engine achieves its maximum output of 92 kW (125 PS) at 3500 rpm.
The maximum torque of 280 Nm is already available to the engine at a speed of 2200 rpm.
A high torque of more than 250 Nm is available over the broad speed range of 1750 to 3250 rpm.
This is characterised by excellent tractive power.
The engine is suitable for so-called bio-Diesel (vegetable-oil methyl ester).
Temperature sender
4
Cylinder order
3 2 1
Intake manifold
Intake-manifold-dependent full-load enrichment
Distributor injection pump
Two-part flywheel
Hydraulic pump for power steering
Viscous fan
Oil pump
Direct drive with crankshaft
197/48
Cylinder 1 is located at the flywheel end.
5

6
Engine - mechanical
The cylinder block of the 2.8 l Diesel engine has been keep very „slim“ to reduce noise. The necessary rigidity is achieved with heavily pronounced ribbing.
Mounting holes for timing gears
Dry cylinder sleeves
Two thermostat valves
Installation opening for oil cooler
Oil filter mount
Lower crankshaft bearing, separate from crankcase to reduce noise
197/41
Additional devices are integrated in the block to reduce noise and leaks.
The baffle plate is used to stiffen the lower cylinder block and to calm the oil surge.
197/43
Baffle plate
197/42

The oil circuit is an important system for lubricating sliding metal parts and for internal engine cooling.
Cylinder order 2 1111
Jets for piston cooling
Turbocharger
Oil pump, driven by crankshaft
Oil pressure valve
Oil cooler
Camshaft
Timing gears h eeee n d
Crankshaft
Pressure relief valve
Oil filter
197/35
7

Engine - mechanical
The two-part flywheel
On internal-combustion piston engines, torsional vibrations are produced at the crank-shaft and flywheel due to the irregularity of the combustion process.
The two-part flywheel prevents these torsional vibrations from being transmitted to the drive train, and from causing resonant vibrations there.
Resonant vibrations are outwardly noticeable as disturbing noises.
The two-part flywheel divides the flywheel mass into two parts.
The primary flywheel mass is one part and belongs to the moment of inertia of the engine. The other part, the secondary mass, increases the moment of inertia of the gearbox.
The two isolated masses are connected with a spring/damping system.
With the moment of inertia of the gearbox components increased in this way, they only absorb vibrations at considerably lower speeds.
„Gearbox rattling“ in the idling speed range can no longer occur.
194/024
8
Vibration damper Crankshaft group
197/18
Primary flywheel mass of two-part flywheel
Vibration isolation
197/45

Ordinary flywheel-clutch design
Flywheel with clutch Clutch disc with torsion damper
Engine and gearbox vibrations in idling speed range
194/025 194/027
The two-part flywheel
Primary flywheel mass Secondary flywheel mass with clutch
Engine and gearbox vibrations in the idling speed range
Torsion damper
(spring/damping system) Rigid clutch disc
194/026 vibrations produced by the engine vibrations absorbed by the gearbox
194/028
9

Engine - mechanical
Timing gears
The camshaft is driven by the crankshaft with intermediate gears.
Cylinder 1 is located on the flywheel end.
Adjustment bearing lever
Intermediate gear
(for camshaft drive)
Injection pump
Camshaft sprocket
Intermediate gear of camshaft
Spacer fork
Coolant pump
Vane pump
Power steering
Intermediate gear to crankshaft
Gear group housing
Intermediate gear
Crankshaft
197/5
Valve timing adjustment
To adjust the valve timing, turn the crankshaft to cylinder 1.
Also turn the camshaft to cylinder 1 (with camshaft sprocket loosened) and lock in place with the camshaft lock 3445.
Then tighten the camshaft sprocket.
The intermediate gears have no marking for adjustment.
10

197/36
The tooth flank adjustment
The tooth flank clearance of the intermediate camshaft gear can be adjusted.
To adjust, insert the intermediate gear in the adjustment bearing lever.
Next the intermediate gear is pivoted downward into the spacer fork with the adjustment bearing lever.
197/37
197/38
Then pivot the intermediate gear with the spacer fork between the large intermediate gear and the camshaft sprocket until the specified tooth flank clearance is achieved.
Then tighten the spacer fork.
This device is patented.
11

12
Engine - mechanical
Injector Sheathedelement glow plug
Direct injection
The new engine is extremely efficient.
The fuel is injected directly into the main combustion chamber.
The injector extends into the cylinder combustion chamber at an angle.
The sheathed-element glow plug is located next to the injector.
In addition to direct injection, there are two design characteristics which make this possible.
– Three-valve technology (2 inlet, 1 exhaust valve)
– Inlet ports shaped as swirl ports
Advantages of three-valve technology are:
– Two inlet valves result in a large inlet crosssection,
– The improved degree of filling of the cylinders.
197/8
The design of the inlet ports
The inlet ports are shaped so that the air flowing in begins to swirl. This supports the intensive mixing of air and injected fuel.
This combination with direct injection, three-valve technology and the swirl port results in intensive combustion.
The pollutant exhaust gas components are considerably reduced.
The emission values drop far below the legal limits.
197/9

Oil jet
Rocker finger
The 2 inlet valves and 1 exhaust valve per cylinder are actuated by the overhead cam via rocker fingers.
Adjustment screw
The rocker finger rests on the adjustment screw on one side and on the valve on the other side.
The cam runs up against the back of the rocker finger.
This actuates the valve.
An oil jet lubricates the cam surface, i.e. the oil film forms a noise cushion.
197/4
Adjusting the valve clearance
Allan key
197/7
Feeler gauge
The valve clearance is mechanically adjusted.
Testing and adjustment are carried out with the engine cold.
A feeler gauge is used to measure the clearance between the cam surface and the rocker finger.
The adjustment is made with an Allan key by screwing the self-locking adjustment screw in or out.
The related cam of the cylinder to be checked must always be facing upward.
13

Diesel direct injection
General overview
The 2.8 l TDI engine operates with
– mechanically controlled, direct injection with a distributor injection pump
– exhaust-gas turbocharger, boost pressure pneumatically controlled with bypass
– boost-pressure-dependent enrichment, pneumatically controlled
– glow plug system, controlled in dependence on engine coolant temperature
– intercooler for cooling the intake air before it enters the intake manifold
– pre-heated fuel filter
Bypass
14
D = Ignition/starter switch
G62 = Coolant temperature sender
J52 = Glow plug relay
K29 = Glow period warning lamp
Q6 = Glow plugs
Exhaust-gas turbocharger
Intercooler

Q6
G62
J52
K29
D
Fuel filter
Distributor injection pump
C olllloo diiiinn
= Output signal g////LLLLeee geee d
= Input signal
= Positive
Fuel tank
= Fuel supply line
= Fuel return line
= Air
= Exhaust
197/10
15

Diesel direct injection
The fuel supply
The fuel is sucked in directly via the fuel filter from the fuel tank by the feed pump in the distributor pump housing.
The fuel is then carried via the high-pressure pump section of the distributor injection pump to the injectors for injection.
Excessive fuel flows back to the fuel tank via a return line.
Injector
16
Distributor injection pump
Pressure line
Return line
Suction line
Fuel filter
Fuel tank 197/11

The distributor injection pump
Quantity adjuster for boost-pressure enrichment
Centrifugal governor
Fuel inlet Fuel cut-off
Feed pump
197/25
Roller ring Eccentric disc Distributor piston
Injection distributor High-pressure pump
197/49
The high-pressure pump
In the high-pressure pump the distributor piston is moved forward by the eccentric disc and produces the necessary pressure on the enclosed fuel, which is carried via the distributor duct to the injectors for injection.
When replacing the distributor-type fuel injection pump, the new pump must be filled with fuel.
17

Diesel direct injection
The injection
Filling hole
Control slit
Filling
Turn the distributor piston to align the filling hole with the control slit.
The pressurised fuel flows into the highpressure chamber.
Distributor piston
197/39
Injectors
The distributor piston continues to turn. The control slit and filling hole are no longer aligned.
The distributor piston is moved forward by the eccentric disc and the fuel is pressed toward the injector via the distributor duct.
18
Distributor duct
197/40

Filling hole
High-pressure chamber
Solenoid valve
N109
Spring
Armature
197/2
The fuel cut-off
To shut off the engine, the solenoid valve N109 closes off the fuel supply hole.
The solenoid valve consists of a coil and an armature with a pressure spring.
When the ignition is switched on, the coil is supplied with voltage and pulls in the armature against the force of the spring.
The armature of the solenoid valve, which simultaneously acts as a check valve, holds open the filling hole to the high-pressure chamber.
After the ignition is switched off, the voltage supply is interrupted.
The magnetic field collapses.
The spring presses the armature onto the valve seat.
The filling hole is closed off.
The engine stops.
Electrical circuit
15
N109
31
197/3
Effects in case of failure
If the solenoid valve is defective or the voltage supply is interrupted, the engine stops.
19

20
Diesel direct injection
The speed control
The centrifugal governor controls the idling speed and cuts off the injection quantity at maximum speed.
Start
With the engine stopped, the leaf spring pushes the starting lever to the left.
In the process, the control valve moves to the right.
The distributor piston must carry out a long stroke until the cut-off hole is free.
With this device the starting quantity is increased.
Leaf spring
Starting lever
Control valve
Distributor piston
Cut-off hole
Stroke for start quantity
197/30
Idling
If the engine is revved-up, the centrifugal weights move the governor sleeve.
The starting lever is positioned on the tensioning lever.
This causes the control valve to move to the left.
The cut-off hole is opened above the idling speed.
Control takes place via the idling spring with a balanced force ratio between the centrifugal force and the idling spring.
Starting lever
Centrifugal weights
Idling spring
Tensioning leve
The stroke of the distributor piston is determined by the eccentric disc.
Control valve
Stroke for idling
197/31

Acceleration/Part throttle
The tensioning lever is pulled to the left with the drag element.
This causes the control valve to move to the right.
The stroke up to the opening of the cut-off hole becomes greater, thus increasing the injection quantity.
The engine revs accordingly.
The spring in the drag element still acts as a rigid connection.
Drag element
Control valve
Cut-off hole
Tensioning lever
Full throttle - cut-off
When the speed increases further, the forces of the centrifugal weights also increase.
This presses together the control spring in the drag element.
The control valve moves far to the left so that the cut-off hole is opened.
As a result, a pressure build-up in the distributor piston is prevented and the cut-off speed is reached.
Control spring
Stroke for art throttle
Stop screw
197/32
Correction lever
Pressure spring
197/33
21

22
Diesel direct injection
The injection distributor
As the engine speed increases, injection must be advanced.
This task is assumed by the injection distributor.
Injection distributor
The injection distributor has been turned by 90 o
for improved illustration.
Roller ring Roller Eccentric disc
197/28
197/44
Pump housing
Driver
Piston
Roller ring
Roller
197/29
197/50
Function
As the speed increases, the feed pump in the distributor injection pump increases the pressure in the distributor pump housing.
The increasing pressure also acts on the piston of the injection distributor.
The piston is deflected and turns the roller right against the rotating direction of the distributor piston via the driver.
The eccentric disc runs up against the cam earlier so that injection is carried out earlier.

The injectors are two-spring jets. They spray the fuel directly into the cylinder in two stages. This results in "soft" combustion and reduced combustion noise.
Two-spring jet holder
Spring 1
Spring 2
Gap for stroke 2
Gap for stroke 1
Stroke 1
197/23
Stroke 2
197/24
Jet needle
197/22
Function
The injector is designed as a fivehole jet.
There are two springs of different strengths located in the jet holder.
The springs are matched so that at the start of injection, the jet needle is only lifted against the force of spring 1.
197/46
A small quantity of fuel is preinjected at low pressure through the resulting small gap.
This pre-injection provides a gentle increase in the combustion pressure and creates the ignition conditions for the main fuel quantity.
As the injection pump feeds more fuel than can flow through the small gap, the pressure in the injector increases. The force of spring 2 is overcome and the jet nozzle is lifter further. Now the main injection is carried out at a higher injection pressure.
23

Diesel direct injection
The boost-pressure enrichment adapts the fuel quantity to the air mass.
Full-throttle enrichment
Boost-pressure valve Diaphragm
Boost pressure from intake manifold
Push rod small diameter
24
197/15
Control valve Distributor piston
Task
Adapt fuel quantity to the air filling of the cylinders:
– more air (due to turbocharging) = ensure high fuel supply
– reduced air mass = reduce fuel supply
An increasing boost pressure increases the cylinder filling, and more fuel must be injected accordingly.
This is achieved by adjusting the usable stroke of the distributor piston.
The adjustment is pneumatic-mechanical.
The high boost pressure presses the diaphragms in the boost-pressure valve downward. The pin resting on the diaphragm push rod glides from the large to the small diameter of the push rod.
This causes the control valve on the distributor piston to be moved to the right via the lever mechanism.
The usable stroke increases and more fuel is injected.

Idling/Part throttle
Diaphragm
Push rod large diameter
197/16
No enrichment is required at idle and at part throttle.
The boost pressure is not high enough to overcome the spring force under the diaphragms.
The spring pushes the diaphragms upward.
The pin is now resting on the large diameter of the push rod.
The lever mechanism moves the control valve to the left.
This reduces the usable stroke of the distributor piston.
Less fuel is injected.
25

26
Diesel direct injection
Fuel filter
Bimetal control valve
In the fuel filter mechanical impurities and water are kept out of the distribution injection pump.
As the specific weight of water is higher than that of
Diesel fuel, water collects in the lower section of the filter housing.
Return line from injection pump
Suction line
Water can collect during refuelling or due to the presence of condensed water in fuel.
– The water should be drained off in autumn before the winter period.
– Failure to change the filter at proper intervals may result in damage to the distributor injection pump.
Filter
Water drain screw
Bimetal control valve closed
Return line to fuel tank
197/12
The fuel pre-heating
At lower temperatures Diesel fuel tends to separate out paraffin, which clogs the fuel filter.
To prevent this, the heated fuel flowing back from the pump is used for „pre-heating“ in the filter.
Depending on the temperature, the bimetal control valve routes the fuel to the filter again or into the fuel tank.
At a temperature above +31 o
C the bimetal control valve is in the rest position, and the path to the filter is closed. The fuel flows to the fuel tank.
Bimetal control valve open
At a temperature below +15 o
C the bimetal control valve opens the passage to the filter and fuel flows to the filter.
197/13
197/14

The turbocharger is driven with the exhaust gas to compress the air required for combustion.
The air quantity per work cycle is increased.
The result is a power increase with the same displacement and at the same speed.
Waste gate
Bypass
Intercooler
Air cleaner
Turbine
197/17
Turbocharger Compressor impeller
The turbocharger contains a turbine and a compressor impeller on a common shaft.
With these the energy contained in the exhaust gas is transmitted to the compressor side.
At a certain boost pressure the boost pressure controller opens.
Part of the exhaust gas flows past the turbine.
The turbocharger speed drops.
The speed may be over 100,000 rpm.
As the turbocharger speed increases, so does the boost pressure.
In order not to endanger the life of the engine, the boost pressure is limited.
This task is assumed by the boost-pressure controller.
An output increase is also achieved through the use of an intercooler. The combustion air sucked in by the turbocharger via the air cleaner is particularly strongly heated in the turbocharger on the way to the engine. The air density, and thus the oxygen content, drop.
In the intercooler it is cooled down again, whereby the air density increases. Then the air is pressed into the combustion chamber.
27

28
Glow plug system
The AGK engine is equipped with a controlled glow plug system. The glow plug relay is connected to a glow period control unit.
If the engine it to be started at low temperature, the coolant temperature sensor G62 determines the preheating time.
Preheating is initiated with the ignition/starter switch
D.
It is indicated with the glow period warning lamp.
When the glow period warning lamp goes out, the preheating time for starting has been reached.
Preheating is continued for a certain period after the glow period warning lamp goes out
(ready time).
During this time the engine should be started.
If the engine is not started within the ready time, the connection on Terminal 50 of the control unit from the glow plug relay ensures that heating takes place as long as starting continues.
Following starting a after-glow phase begins.
In the after-glow phase, heating takes place for a few seconds dependent on the temperature. After glowing supports the warm-up phase, has a positive effect faultless, low-smoke engine operation and reduces exhaust emissions, e.g. the emission of unburned hydrocarbons.
If the engine has not been started within a certain time, the safety switch-off ends pre-heating.
120
80
40
1/1
1/2
0
60
80
100 120 km/h
140
40
20 km
160
180
200
ABS
ABD
20
30
40
50
10
60
70
9
12
3
6
SRS
197/21
The glow plug relay with the thermo fuse for the glow plugs is located on the auxiliary relay carrier in the engine compartment at the left.

30
15
K29
D
30
B
50
T6/6
50
T6/2
J52
T6/4
31
T6/3
15
T6/1
1 2 3 4
S39
80A
+
-
A
30
15
G62
Q6
31
The current flow diagram of the glow plug system with control unit
A
B
= Battery
= Starter
D = Ignition/starter switch
G62 = Coolant temperature sender
J52 = Glow plug relay
K29 = Glow period warning lamp
S39 = Thermo fuse for engine glow plugs
31
197/26
29

Self check
Which answers are correct?
Sometimes only one.
But maybe more than one – or even all of them!
Please fill in the blanks.
30
1.
It is
A.
the intermediate gear for the crankshaft.
B.
the intermediate gear of the camshaft.
3.
Valve actuation takes place
A.
directly with the overhead cam,
B.
via rocker arms,
C.
via rocker fingers.
2.
The timing gears for driving the distributor injection pump and the camshaft are located on the .............................. .
The cylinders are numbered starting on the .............................. end
?
Adjustment is carried out by pivoting the .................................. .
4.
Full throttle enrichment is a measure for adapting the .............................. of the air filling of the cylinders.
It takes place .............................. .
The boost pressure is tapped off at the .............................. .

5.
To pre-heat the Diesel fuel,
A.
the glow period control is used,
B.
the heated fuel flowing back from the pump is used in the filter,
C.
engine coolant flows around the filter.
7.
6.
The duration of the pre-heating and after-glow period of the glow plugs is
A.
manually influenced by operating the starter switch,
B.
controlled via a glow period control unit,
C.
is determined by the coolant temperature sensor.
The control pressure for wastegate is
A.
tapped off at the compressor air outlet,
B.
tapped off at the intake manifold air outlet,
C.
also controlled by the glow plug relay via a solenoid valve.
8.
To save space, the .............................. and the ..............................
are integrated in the cylinder block without intermediate lines.
9.
Which of the following statements are false?
A.
The combination of direct injection, three-valve technology and swirl port results in intensive combustion.
B.
The fuel is injected in 2 stages.
C.
The distributor injection pump operates with the full throttle stop in dependence on the atmospheric pressure.
10.
The injector is a .............................. .
Injection is carried out directly .............................. above the piston.
Injection in 2 stages is achieved with .............................. in the jet holder.
engths erent str
, spacer fork; 4. fuel quantity, pneumatic-mechanically
?
, intake manifold; 5. B; 6. B, C;
, in the combustion chamber, 2 springs of diff , thermostat housing; 9. C; 10. 5-hole jet
1. C; 2. flywheel end, output; 3. B
7. A; 8. oil cooler
Solutions:
31

Only for internal use. © VOLKSWAGEN AG, Wolfsburg
All rights and technical changes reserved
740.2810.16.20 Published: 08/97
❀ This paper was made from woodpulp bleached without using chlorine.