WSM_01!03!01_en.11,12 and 16 Litre Engine

01:03-01 Issue 4

11, 12 and 16 litre engines

123 134

Function description

ã Scania CV AB 2003, Sweden

1 585 748

en

Contents

Contents

2

Combustion and exhaust gases

.................................................................................. 3

Cylinder block

.................................................................................. 8 Cylinder liner............................................................ 9

Valve mechanism

................................................................................ 10

Crank mechanism

................................................................................ 12

Timing gear

................................................................................ 17

Fan drive

................................................................................ 21

Lubrication system

................................................................................ 23

Turbocharger

................................................................................ 31


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The function description applies to the new DC11 type 11 litre engine, i.e. the 11 litre engine which has 4 valves/cylinder.

Combustion and exhaust gases When diesel fuel is combusted, diesel exhaust gases are formed. The constituents in the exhaust gases that are regulated by law are: •

Nitrogen oxides, which are poisonous and contribute to photochemical smog and ground level ozone and also eutrophication and acidification.

•

Hydrocarbons, which give diesel exhaust gases their characteristic smell and contribute to photochemical smog and ground level ozone.

•

Particles which are considered to be harmful to people's health.

•

Carbon monoxide, which is a poisonous gas. The content of carbon monoxide is very small in diesel exhaust gases because there is a large surplus of air in a diesel engine.

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Nitrogen oxides, NOx The atmosphere contains: 80% Nitrogen and 20% Oxygen. N + O2

NO + NO2

•

Lower the combustion temperature.

•

Reduce the quantity of oxygen during combustion.

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When air is subjected to high temperatures, the nitrogen and oxygen in the air react and nitrogen oxides are formed. In order to reduce the discharge of nitrogen oxides, it is possible to:

N= nitrogen O2= oxygen The combustion temperature can be lowered by: •

Charge air cooling.

•

Water injection.

•

Re-circulation of exhaust gases.

•

Delayed injection timing.

NO+NO2=NOx=nitrogen oxides

The quantity of oxygen in the combustion chamber can be reduced by: •

Re-circulation of exhaust gases.

•

Reduced rotation of air in the combustion chamber.

A high injection pressure produces smaller fuel droplets which gives a higher concentration of oxygen around each fuel droplet, which in turn leads to the increased production of nitrogen oxides. Most methods to reduce the nitrogen oxides also reduce the efficiency of the engine, which leads to increased fuel consumption which in turn leads to the increased production of carbon dioxide.

4


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Hydrocarbons, HC Hydrocarbons are waste products of the fuel and result from incomplete combustion. Hydrocarbons also contain substances which give diesel exhaust gases their characteristic smell. The discharge of hydrocarbons can be reduced by: •

Raised temperature in the combustion chamber.

•

Increased rotation of air in the combustion chamber.

•

Greater atomisation of the fuel.

•

Reduced pressure chamber volume in the nozzle.

•

Increased injection pressure.

•

Catalytic post-treatment.

5 1

3 1 2 3 4 5

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2

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4

Nozzle needle Nozzle hole Pressure chamber volume Needle seat Fuel


5


Particles Particles contain soot and hydrocarbons from fuel plus lubrication oil, sulphuric acid and ash. Particles give rise to smoke and are formed in the event of incomplete combustion, from oil in the combustion chamber and from the sulphur in the fuel. The discharge of particles can be reduced by: •

More air in the combustion chamber.

•

Increased rotation of air in the combustion chamber.

•

Higher injection pressure, smaller holes in the nozzle which in turn means higher temperatures in the combustion chamber.

•

Reduced pressure chamber volume in the nozzle.

•

Smaller quantity of oil in the combustion chamber.

•

Lower sulphur-content in the fuel.

•

With a particle filter.

5 1

3 1 2 3 4 5

6


2

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4

Nozzle needle Nozzle hole Pressure chamber volume Needle seat Fuel

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Conclusion The measures that can be taken to reduce the production of one constituent in the exhaust gases can simultaneously lead to an increase in another constituent.

The relationship between nitrogen oxides, NOx and hydrocarbons, HC E (g/kWh)

The trend today is to: •

Delay the timing of injection in order to lower the combustion temperature, which reduces the production of nitrogen oxides.

NO x

HC

HC

The disadvantage is that the efficiency of the engine is reduced, which leads to increased fuel consumption. A

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NOx

B

A = Early injection time B = Late injection time

•

•

Reduce the quantity of oxygen at combustion, which reduces the production of nitrogen oxides.

The relationship between nitrogen oxides, NOx and fuel consumption NOx (g/Kwh)

Increase the injection pressure, which reduces the production of particles.

1 A

2 115 243

B

Fuel comsumption

1 = Early injection time 2 = Late injection time A = Engine with turbocharger B = Engine with turbocharger and charge air cooler

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Cylinder block

Cylinder block The cylinder block is cast in one piece, and each cylinder has a separate cylinder head. The cylinder bores have wet liners.

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11 and 12 litre engines

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16 litre engine

8


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Cylinder block

Cylinder liner The cylinder liners can be replaced. A steel gasket with vulcanised rubber seals provides sealing between cylinder liner and cylinder head. One gasket per cylinder. The cylinder liner protrudes slightly above the cylinder block surface and presses the gasket against the cylinder head, thus making sure it seals. The vulcanised rubber seals provide sealing against the coolant and lubrication oil channels.

01 1410

The temperature in and around the combustion chamber is very high. The cylinder liner has a low attachment which enables cooling right up to the cylinder head. This reduces the temperature on the piston rings, which results in a longer service life for both piston rings and cylinder liners. The low attachment of the cylinder liner reduces the risk of the liner sinking since the lower temperature reduces the material fatigue.

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Valve mechanism

Valve mechanism The purpose of the valve mechanism is to open and close the valves at the right time according to the crankshaft and piston position. The camshaft is driven by the timing gears and rotates at half the speed of the crankshaft. There are two designs of camshaft for 11 and 12 litre engines. The camshaft has two cams per cylinder on engines with an injection pump and it has three cams per cylinder on engines with a unit injector since the camshaft also drives the unit injector. The 16 litre engine has twin camshafts, one for each line of cylinders. The camshafts have three cams per cylinder. The 16 litre engine is only available with a unit injector. One end of the push rod rests on the roller tappet, and the other end acts on the rocker arm. At one end of the rocker arm there is an adjusting screw. The lower ball-shaped end of the screw rests in the pushrod, making the tappet adjust to the camshaft movement.

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Valve mechanism

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The valve seat inserts are firmly pressed to a tight fit in the cylinder head. The material in the seat inserts is very strong, so the valve seats have a long service life. If required the valve seat inserts can be renewed.

With four valves per cylinder the valve area is greater, which makes it easier to fill the cylinder with air. At the same time less power is required to drive out the exhaust gases.

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The effort required for gas flow is reduced and engine efficiency is improved. This in turn leads to a reduction in fuel consumption.

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Crank mechanism

Crank mechanism Pistons There are two different types of pistons. Integrally cast aluminium pistons and articulated pistons. Articulated pistons are split and have an aluminium skirt and a steel crown.

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One of the advantages of articulated pistons is that they withstand more stress than conventional pistons. This allows for a higher engine output.

Engine with articulated piston

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Crank mechanism

The combustion chamber is a recess in the piston crown. It is bowl-shaped with a raised section in the centre. The design of the combustion chamber affects the spinning (air rotation) in the combustion chamber.

In order for the piston to run smoothly there must be a gap between the piston and the cylinder wall. Therefore the piston has two compression rings that seal this space and dissipate the heat from the piston.

The oil scraper ring prevents lubrication oil from the crankcase getting into the combustion chamber and being combusted.

The design of the piston and the piston rings is vital for the reliability, lubrication, oil consumption and fuel consumption of the engine.

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Inside the oil scraper ring there is an expander which presses the ring against the cylinder wall. The expander consists of a coil spring.

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Crank mechanism

Connecting rods The small end of the connecting rod is wedgeshaped. This allows for larger contact surfaces in piston and connecting rod.

The big end of the connecting rod is split diagonally, so that the piston and the connecting rod can be pulled up through the cylinder.

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116 762

To prevent the connecting rod bearing cap and the connecting rod from becoming offset, the contact surfaces have grooves and pins, or they are unmachined fracture surfaces.

Connecting rod with unmachined contact surface

14

Connecting rod with grooved contact surface


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Crank mechanism

Crankshaft Each compression stroke acts to "slow down" the crankshaft and each combustion stroke acts to increase its rotational speed. The pistons and connecting rods change their direction of motion twice per revolution. The power impulses from the connecting rods cause torsional oscillations in the crankshaft. These oscillations are strongest at a specific engine speed. Torsional vibrations have the following effect: Imagine that the rear end of the crankshaft and the flywheel rotate at a constant speed. In relation to the constant speed of the flywheel, the rotational speed of the front end of the crankshaft will increase and decrease several times during each rotation. The material is important for the crankshaft service life. Strict requirements also apply to design and surface treatment. For example, the surface finish of the shaft journals is vital in preventing fatigue failure.

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Crank mechanism

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The bearing surfaces on the crankshaft are hardened to such a depth that they can be re-ground in several stages.

The bearing shells of the main bearings and the connecting rod bearings consist of three layers. The outer layer is steel, the mid layer lead bronze, and the inner layer is lead and indium or lead, tin and copper. The inner layer will normally wear off.

For the axial location of the crankshaft, the rear main bearing has thrust washers. These thrust washers are available in various thickness, keeping the axial clearance maintained after grinding.

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Timing gear

Timing gear The timing gears are located at the rear end of the engine. Important components such as the injection pump, unit injector and valve mechanisms require precise control. They are attached to the rear end of the crankshaft, close to the flywheel, where the crankshaft rotation is the smoothest.

11 and 12 litre engines with injection pump The crankshaft gear drives two intermediate gears and the oil pump gear. One of the intermediate gears drives the camshaft. The camshaft gear in turn drives the injection pump and the hydraulic pump. The other intermediate gear drives the air compressor.

6

5

The camshaft and the injection pump rotate at half the speed of the crankshaft.

7

4

3

1

1 2 3 4 5 6 7

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2

Oil pump gear Air compressor gear Crankshaft gear Intermediate gear Injection pump gear Camshaft gear Power steering pump gear


17

Timing gear

01 1407

To facilitate assembly the gears have markings, either on a tooth or in a tooth gap. The injection gear has an oval hole for setting the injection timing (α-angle).

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Timing gear

11 and 12 litre engines with unit injector

The crankshaft gear drives two intermediate gears and the oil pump gear. One intermediate gear drives the camshaft, air compressor and hydraulic pump. The other intermediate gear drives the power take-off and on buses it also drives a hydraulic pump which in turn drives the fan motor.

Engine with unit injector 1 Oil pump gear 2 Crankshaft gear 3 Intermediate gear 4 Hydraulic pump gear 5 Compressor gear (compressed air) 6 Camshaft gear 7 Power take-off

113 528

To facilitate assembly the gears have markings, either on a tooth or in a tooth gap.

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Timing gear

16 litre engine

7

5

4

3 10

8

The crankshaft gear drives both camshafts and the oil pump via an intermediate gear. One camshaft gear in turn drives the compressor.

9

One camshaft has a gear at the front end, which drives the hydraulic pump and the feed pump. The camshafts rotate at half the speed of the crankshaft.

6

1 2 3 4 5 6 7 8 9

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2

1

Crankshaft gear Intermediate gear (power take-off) Intermediate gear Camshaft gear Compressor gear Oil pump gear Front camshaft gear Hydraulic pump gear Feed pump gear

10 Power take-off drive gear

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To facilitate assembly the gears have markings, either on a tooth or in a tooth gap.

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Fan drive

Fan drive 11 and 12 litre engines There are two different belt drive designs. A new design was introduced in September 1997. The different designs are not interchangeable. Old design The fan is driven by the crankshaft by way of a clutch with rubber segments.

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To reduce oscillations at the front end of the engine there is a vibration damper, and there is also a fan coupling which is adjusted so that it too operates as a vibration damper. New design The fan is driven by the crankshaft. A vibration damper is used to reduce oscillations at the front end of the engine.

Old design

New design

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Lubrication system

Lubrication system 8 A piston cooling valve (located in the oil cooler housing on 11 and 12 litre engines and in the front timing gear casing on 16 litre engines).

In addition to the oil sump, the lubricating system consists of the following items. 1 An oil strainer

9 A oil pressure sensor (located in the oil filter housing on 11 and 12 litre engines and in the front timing gear casing on 16 litre engines).

2 An oil pump 3 A safety valve (located in the oil pump) 4 An oil cooler 5 An oil cleaner 6 A relief valve (located in the oil cleaner housing on 11 and 12 litre engines and in the front timing gear casing on 16 litre engines). 7 An oil filter

4, 8

9

9

2, 3

1

5, 6

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7

116 639

8

6

4

5

7

11 and 12 litre engines

1

116 457

2, 3

16 litre engine

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Lubrication system

Oil flow The oil pump draws lubrication oil from the oil sump via the oil strainer. After the oil pump, the lubrication oil passes a safety valve. If the oil pressure exceeds 9.5 bar, the safety valve opens and feeds the lubrication oil back to the oil sump. Too high oil pressure could cause excessive stress to the oil pump and other components in the lubrication system. The lubrication oil then passes through the oil cooler. Some of the lubrication oil is passed through the oil cleaner. After cleaning, the oil is fed back to the oil sump. The rest of the lubrication oil passes through a relief valve which regulates the pressure in the oil system. Surplus oil is drained back to the oil sump. The lubrication oil passes on to the oil filter for cleaning.

Oil flow in the 12 litre engine

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Lubrication system

Lubrication oil reaches the camshaft bearings and crankshaft main bearing via ducts in the cylinder block.

The channel is constantly pressurised. The oil is led to the roller tappet shafts via grooves in the camshaft bearing. The roller tappet shafts have drilled ducts for lubricating the roller tappets.

Ducts in the crankshaft lead the lubrication oil to the connecting rod bearings. A direct duct leading from the main duct takes lubrication oil to the rocker arms.

Oil flow to the oil filter in the 16 litre engine 1 2 3 4 5 6

To the cylinder heads To the valve mechanisms To the turbocharger Piston cooling nozzles Relief valve Piston cooling valve

Oil flow from the oil filter in the 16 litre engine

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Lubrication system

The pistons are cooled by the lubrication oil. Oil is sprayed up under the piston crown through special nozzles, one for each cylinder.

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The piston cooling valve opens at between 1.7-2.2 bar. It is located in the oil cooler housing on 11 and 12 litre engines and in the front timing gear casing on 16 litre engines.

768

There is no piston cooling at low speed (idling).

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Lubrication system

Schematic diagram of the oil circulation in the lubrication system 11 and 12 litre engines B 2

3

4

5

6

7

8

A

119 920

1

1 2 3 4 5 6 7 8

Oil sump Oil pump Safety valve Oil cooler Oil cleaner Relief valve Oil filter and by-pass valve Piston cooling valve

1 2 3 4 5 6 7 8 9

Oil sump Oil pump Safety valve Oil cooler Oil cleaner Front timing gear housing Relief valve Oil filter and by-pass valve Piston cooling valve

A = To bearing and turbo B = To piston cooling nozzles

16 litre engine 3

2

4

5

6

7

8

9

A

B

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1

A = To bearing and turbo B = To piston cooling nozzles

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Lubrication system

Oil pump The oil pump is driven by the crankshaft gear and generates the pressure which is necessary for the lubrication oil to reach all the lubrication points.

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The oil pressure must be high enough to ensure that each lubrication point receives the sufficient amount of oil for lubrication and cooling.

Oil pump for 11 and 12 litre engines

Oil cooler All the oil flows through the oil cooler and is cooled by the coolant in the cooling system.

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An opening valve for piston cooling is located in the oil cooler housing on 11 and 12 litre engines.

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Oil cooler for 11 and 12 litre engines

Oil cooler for 16 litre engine

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Lubrication system

Centrifugal oil cleaner The centrifugal oil cleaner has a rotor which is made to rotate by the force of the jet of lubrication oil spraying through two nozzles in the bottom of the rotor. Foreign particles are thrown against the rotor wall where they stick and form a solid coating. The centrifugal cleaner should be disassembled and cleaned in accordance with the intervals stated in the Scania Maintenance Program.

Centrifugal oil cleaner for 11 and 12 litre engines

115 751

A relief valve, regulating the pressure in the oil system, is located in the oil cleaner housing on 11 and 12 litre engines. Surplus oil is drained back to the oil sump.

Centrifugal oil cleaner for 16 litre engine

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Lubrication system

Oil filter The lubrication oil passes on to the oil filter for cleaning. The oil filter is a paper filter. If the filter becomes clogged up, an overflow valve opens. The engine is always supplied with lubrication oil, but if the filter is clogged up the lubrication oil is not cleaned. The overflow valve is fitted in the oil filter retainer or timing gear casing depending on the engine type. The filter for the 16 litre engine has a drain hole and is drained when the filter element is lifted out. The oil filter should be changed in accordance with intervals given in the Scania maintenance programme.

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Oil filter for 11 and 12 litre engines

Oil filter for 16 litre engine

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Turbocharger

Turbocharger The turbocharger increases the air mass in the engine cylinders. The extra air means that the engine can burn more fuel. An engine with a turbocharger thus produces a higher power output than the same engine without a turbocharger.

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The turbocharger consists of a turbine and a compressor. The turbine is driven by the engine exhaust gases. The compressor compresses the engine intake air.

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Turbocharger

The compressor wheel and turbine wheel are located on the same shaft. The bearing housing is situated between the compressor and the turbine. When the engine output increases, the engine produces more exhaust gases. This increases the speed of the turbine wheel, and thus of the compressor. The air mass is thus automatically adjusted to the requirements of the engine, and no separate regulating system is required.

The shaft is mounted on two radial bearings and one thrust bearing rotating freely in the bearing housing. The bearing housing is sealed off from the turbine and the compressor with sealing rings.

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The compressor and turbine wheels rotate very rapidly. At full output the speed of rotation is at about 100,000 rpm. At the same time the temperature at the turbine wheel is above 600°C. This places great demands on the rotating parts, on balance, cooling and lubrication. If the turbine or compressor wheels are damaged, the turbocharger must be renewed.

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Turbocharger

A blocked air filter will cause excessive vacuum in the intake pipe. There is then a risk of oil mist being drawn from the bearing housing. If the sealing ring on the turbine side is worn, the exhaust gases will be blue when idling. Foreign particles, e.g. grains of sand or metal particles, in the turbine or the compressor will ruin the vanes of the wheel. This will lead to imbalance and bearing wear. The power output of the engine decreases, and if the engine is still running the reduced air supply may cause overheating and engine damage. This type of overheating is not visible on the coolant temperature gauge. Even small leaks in the line between the air filter and the turbocharger will cause dirt to be deposited on the compressor wheel. The charging pressure is reduced which results in an increase in the exhaust gas temperature and smoke and leads to a reduction in the service life of the engine. Leaks in the exhaust pipe between the cylinder head and the turbocharger will result in a low charge pressure. Some engines have a smaller turbine, providing a higher charge pressure, to meet the demands in terms of smoke and fuel consumption at low engine speeds.

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Turbocharger

Some engine types are equipped with a wastegate valve. The function of the wastegate valve is to reduce the pressure so that the maximum speed of the turbocharger is not exceeded.

Turbocharger without wastegate valve

101749

101750

When the pressure in the compressor housing becomes too high, the wastegate valve opens. The exhaust gases move past the turbine through a by-pass tube and the rotation speed in the turbocharger is reduced.

Turbocharger with wastegate valve

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7

4

1 3

5

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6

1 2 3 4 5

34

Air in Air to the engine Exhaust gases from the engine Exhaust gases out Pressure regulator

6 By-pass tube 7 Compressor 8 Turbine 9 Wastegate valve


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WSM_01!03!01_en.11,12 and 16 Litre Engine

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