01:01-01 Issue 2
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9 litre engine Function description
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© Scania CV AB 1998-12, Sweden
Contents
Contents Function description
Valve mechanism ........................................... ........................................... 3 Cylinder block ........................................... ............................................... .... 4
Cylinder liner .............................................. .................................................. .... 4 Crank mechanism ......................................... ......................................... 6
Pistons............................................................. Pistons.......................................... ................... 6 Connecting rods .............................................. .............................................. 8 Crankshaft....................................................... Crankshaft........................................ ............... 9 Crankcase ventilation....................... ventilation.................................... ............. 10 Timing gear ........................................... ................................................. ...... 11
Gear transmission ......................................... ......................................... 11 Lubrication system ..................................... ..................................... 12
Oil pump ............................................. ....................................................... .......... 12 Oil cooler ............................................ ...................................................... .......... 12 Lubrication oil cleaner..................... cleaner .................................. ............. 13 Oil filter .............................................. ........................................................ .......... 14 Lubrication oil ducts ..................................... ..................................... 14 Turbocharger............................................. ............................................... .. 16 Charge air cooler ........................................ ........................................ 19 Fan ........................................... ................................................................ ..................... 20 Belt transmission ......................................... ......................................... 21
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© Scania CV AB 1998, Sweden
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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 gears in the transmission, making it rotate at half the crankshaft rotation speed. The cams of the camshaft, two for each cylinder, actuate the tappets.
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One pushrod end rests in the tappets and the other end actuates the rocker arms. In one end the rocker arm has an adjusting screw. The lower ballshaped end of the screw rests in the pushrod, making the tappet adjust to the camshaft movement.
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The valve seat rings are tightly fitted in the cylinder head. The material in the seat rings is very strong, so the valve seats have a long service life. If required the valve seat rings can be replaced.
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Cylinder block
Cylinder block The cylinder block is cast in one piece and the cylinders are covered by six separate cylinder heads. The pistons run in wet cylinder liners.
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Cylinder liner The cylinder liners can be replaced. A steel gasket with vulcanized rubber seals provides a seal between cylinder liner and cylinder head. The cylinder liner protrudes slightly from the cylinder block and presses the gasket against the cylinder head to seal. The vulcanized rubber seals seal the coolant and lubrication oil ducts.
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Cylinder block
The lower part of the cylinder liner is somewhat flexible to allow thermal expansion. The seal consists of three rubber rings on different levels around the lower part of the liner. Between the two lower rings there is a check bore leading to the outside of the cylinder block. If coolant flows through either one of the holes the sealing rings are leaking. This serves as a warning, indicating that the sealing rings should be replaced.
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Crank mechansim
Crank mechanism Pistons
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The pistons are made of an aluminium alloy. This alloy provides the piston with high strenght, low weight, little thermal expansion and good dissipation of heat. In order for the piston to resist the high pressures and temperatures in the combustion chamber the material of the piston crown and the ring area is thicker than the material in the rest of the piston.
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Crank mechansim
A recess in the piston crown forms the combustion chamber. It is bucket shaped with an elevation in the middle. The reason is to get as high rotation of the incoming air as possible. When the fuel is injected at the end of the compression stroke it mixes well with the air due to the turbulence. This results in efficient combustion.
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To enable the piston to run easily, space between the piston and the cylinder wall is neccessary. Therefore the piston has two compression rings that seal this space and dissipate the heat from the piston. The upper ring is exposed to higher temperature and pressure than the lower one. The strain on the upper piston ring groove therefore gets particularly high. To reduce wear a cast iron ring is cast in the piston.
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The oil ring prevents lubrication oil from the crankcase to get into the combustion chamber. Inside the ring there is an expander that pushes the ring against the cylinder wall. The expander consists of a coil spring. The piston and piston ring design is important for the operational reliability of the engine, lubrication, oil and fuel consumption.
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Crank mechansim
Connecting rods The small end of the connecting rod is wedgeshaped. This results in bigger bearing areas in the piston as well as in the connecting rod.
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The big end has a diagonal split, allowing the piston and connecting rod to be pulled out through the cylinder. The contact surfaces have grooves to prevent the connecting rod bearing caps and the connecting rod from getting offset.
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Crank mechansim
Crankshaft Every compression stroke slows the crankshaft down and every combustion stroke aims to increase the rotation speed. The pistons and connecting rods change their direction of motion twice per revolution. Therefore the crankshaft is exposed to many power impulses every revolution. The material is important for the crankshaft service life. High demands are also made on design and surface treatment. The shaft journal surface quality is important for the protection against fatigue failure.
The bearing areas on the crankshaft are hardened so deep that they can be regrinded at many stages.
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The main bearing and connecting rod bearing shells consist of three layers. The outer layer is made of steel, the middle layer of lead bronze and the layer closest to the crankshaft is made of lead and indium or of lead, tin and copper. The inner layer normally wears down during engine use.
For the axial location of the crankshaft, the rear main bearing have thrust washers. These thrust washers are avaliable in various thickness, keeping the axial clearance the same after grinding.
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Crank mechansim
Crankcase ventilation The crankcase is ventilated via the timing gear housing, leading the crankcase gases to a channel system in the crankcase ventilation unit. The crankcase gases contain oil. The lubrication oil is deposited on the channel walls, runs down to the bottom of the crankcase ventilation unit and back into the crankcase through the crankcase ventilation unit cover plate holes. The passage through the crankcase ventilation unit and the in- and outlets must not be blocked, in order for gas and oil to flow easily through the crankcase ventilation. Otherwise the lubrication oil in the crankcase may be drained via the turbocharger.
There is a small vacuum present in the crankcase. The vacuum is a result of the crankcase ventilation unit outlet being connected to the turbocharger suction side. A diaphragm is used to control the crankcase vacuum. The diaphragm closes the crankcase ventilation unit outlet to the turbo if too much vacuum is created on the turbo suction side. This can happen at high engine load. The oil separator does not prevent small amounts of oil getting into the engine inlet system together with crankcase ventilation gases. Oil that come with the crankcase ventilation gases can be seen as a thin oil film in the charge air system.
Crankcase ventilation for 9 litre engine seen from the outside and in section .
Note.
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Inlet from the timing gear housing
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Diaphragm
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Hole closed by a diaphragm at too large a vacuum on turbocharger suction side.
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Vents for precipitated lubrication oil.
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Outlet to turbocharger suction side
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Timing gear
Timing gear Gear drive 5
Important components such as the injection pump and the 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. The gear wheel on the crankshaft drives two intermediate gears. One of the intermediate gears drives the camshaft and the injection pump. The camshaft gear in turn drives the air compressor and the hydraulic pump. The other intermediate gear drives the power take-off.
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1 Crankshaft gear
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2 Hydraulic pump 3 Air compressor 4 Camshaft 5 Intermediate gear 6 Injection pump 7 Power take-off 8 Intermediate gear 9 Oil pump The camshaft and the injection pump rotate at half the crankshaft rotation speed. In order to facilitate the assembly, the gears are marked on a tooth or in a gap between the teeth. The injection gear has an oval hole for setting the injection timing (a-angle).
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Lubrication system
Lubrication system An oil pump driven by the crankshaft gear creates the circulation needed for the lubrication oil to reach all lubrication points and to flow through the oil cleaner and oil cooler.
Oil pump The lubrication oil coming from the oil sump passes a strainer before it reaches the oil pump. The lubrication oil passes an oil pressure valve after the oil pump. The valve controls the oil pressure by letting some of the lubrication oil return to the oil sump. Otherwise the oil pressure could get too high, especially when the lubrication oil is cold. If the oil pressure gets too high, the oil pump and other parts in the lubrication system could be overstrained. The oil pressure must be high enough to allow enough lubrication oil needed for lubrication and cooling to reach their lubrication points.
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Oil cooler The lubrication oil runs from the oil pump to the oil cooler via channels in the cylinder block. The whole oil flow passes through the oil cooler and is cooled down by coolant from the cooling system.
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Lubrication system
Lubrication oil cleaner The centrifugal cleaner has a rotor that rotates as a reaction to lubrication oil being sprayed from two nozzels at the bottom of the rotor.
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Dirt particles are slung against the rotor wall where they stick. The rotor should be disassembled and cleaned at specified intervals.
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Lubrication system
Oil filter The lubrication oil going to the turbocharger has to be very clean. Therefore the oil passes yet another cleaning step. This cleaning step consists of a filter cartridge with a paper filter. In the filter cartridge there is also a valve that allows oil to get into the turbocharger, in case the filter gets blocked. The filter has to be changed according to intervals given in the Scania maintenance programme.
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Lubrication oil ducts Lubrication oil reaches the camshaft bearings and crankshaft main bearing via ducts in the cylinder block. Ducts in the crankshaft lead the lubrication oil to the connecting rod bearings. The lubrication oil for the rocker arms is led through ducts in two of the camshaft pivot pins. The ducts are opened once every crankshaft revolution. Thus the right amount of lubrication oil reaches the rocker arms.
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Lubrication system
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The engine lubrication oil cools the pistons down. Specific nozzles, one per cylinder, spray oil under the piston crowns. There is a valve in the piston cooling nozzle line. When the oil pressure exceeds 3 bar it opens, and lubrication oil is sprayed through the nozzles.
When the oil pressure is below 3 bar (low engine speed) this special cooling of the piston is not needed. The valve is closed.
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Turbocharger
Turbocharger The function of the turbocharger is to increase the quantity of air for the engine cylinders. The design of the combustion chamber together with the quantity of air and injected fuel increases the power output of the engine. The turbocharger consists of a turbine and a compressor. The turbine is driven by the engine exhaust. The engine intake air is compressed by the compressor.
The compressor wheel is fitted on the same shaft as the turbine wheel. The bearing housing is situated between the compressor and the turbine. Higher power output from the engine results in more exhaust gases. More exhaust gases means that the turbine wheel and therefore the compressor rotate faster. In this way the quantity of air is adapted to the engine requirements without any specific control devices.
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The turbocompressor wheel rotates very fast. At full output the rotation speed is about 100 000 rpm. At the same time the temperature of the turbine wheel is above 600 ˚C. This places great demands on the rotating parts, both for balance, cooling and lubrication. The shaft is mounted in two radial bearings rotating freely in the bearing housing. The seal between the bearing housing to the turbine and the compressor is made by sealing rings which are similar to piston rings.
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Turbocharger
In order to meet legal emission requirements at low engine speed, some engines have a smaller turbine providing a greater charge pressure and therefore less emissions. To prevent the turbocharger from overrevving at high engine speeds, the turbine has a small wastegate valve.
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Turbocharger without wastegate
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. Accordingly, the function of the wastegate valve is to protect the turbocharger from overrevving and the engine from labouring.
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Turbocharger with wastegate
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6 By-pass tube
2 Air to the engine
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3 Exhaust gases from the
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9 Wastegate valve
5 Pressure chamber
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Turbocharger
If the air cleaner is blocked, the vacuum in the intake tract becomes too high. In that case oil mist might be sucked out from the bearing housing into the compressor and from there into the engine. If the sealing ring on the turbo side is worn, the exhaust gases turn blue when the engine is running on idle speed. If the oil drain pipe from the turbocharger is damaged, oil might be emitted from the seals because of the lubrication oil pressure. Foreign bodies, for example a grain of sand or metal swarf in the turbine or in the compressor can damage the rotor blades. This affects the balance and causes bearing wear. The power output from the engine decreases and if the engine is not switched off, damage through overheating may occur because of the reduced quantity of air supplied. This kind of overheating is not indicated by the coolant temperature gauge. Note: Never try to align a damaged blade. It is then often broken during operation causing the turbo to break down completely, which also can damage the engine.
Even very small leaks in the tube between the air cleaner and the turbocompressor may lead to the compressor wheel being contaminated by small particles of dirt. The charge pressure becomes reduced and as a result the exhaust temperature and the quantity of smoke will both rise. This will also cause unnecessary wear of the engine. Exhaust leaks between the cylinder head and the turbocompressor also cause a low charge pressure.
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Charge air cooler
Charge air cooler The outlet air from the turbocharger goes through a line to the charge air cooler, mounted in front of the radiator.
The charge air is cooled by the ram air and the fan, and then passes through the charge air cooler. After beeing cooled down, the inlet air is led to the intake manifolds, which distribute the air to the cylinders.
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Fan
Fan Fan drive The fan is driven by the crankshaft. The power impulses from the connecting rods cause torsional oscillations in the crankshaft. These oscillations are strongest at a specific engine speed. The rear end of the crankshaft and the flywheel rotatate at a constant speed throughout the whole rotation. The front end of the crankshaft will increase and reduce its rotation speed many times per rotation in relation to the flywheel.
A crankshaft vibration damper is used to reduce oscillations at the front end of the engine. A steel ring is fitted on the ringshaped, closed crankshaft damper housing. The housing is fixed to the crankshaft. A sticky oil slows the mutual movement between ring and housing. Since the ring aims at rotating at a constant speed, the oscillation at the front end of the crankshaft is dampened.
The oscillations can cause noise from the transmission gears and in extreme cases even break the crankshaft.
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Belt transmission
Belt transmission The belt transmission drives the coolant pump, the AC compressor and the alternator. The belt is a V-belt and the tension is adjusted through the alternator mounting.
9 litre engine with AC
9 litre engine without AC
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Alternator and belt tensioner
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AC compressor
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Crankshaft
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Coolant pump
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Crankshaft
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Coolant pump
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Alternator and belt tensioner
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