Part 2
Engine
EXTERNAL VIEW
OVERVIEW
The Si6 petrol engine is a 3.2 liter, inline 6-cylinder, naturally aspirated unit, with 4 valves per cylinder, operated by 2 overhead camshafts. The engine emissions comply with EURO 4 (European Union emission regulations) and Ultra Low Emissions Vehicle (ULEV) II legislative requirements and employs catalytic converters, electronic engine management control and pressure controlled crankcase ventilation to limit the emission of pollutants. The cooling system is a low volume, high velocity system. The Engine Control Module (ECM) controls the fuel injection system and the ignition system.
The cylinder block is of aluminum alloy construction with cast iron liners and a pressed aluminum bedplate section bolted to the bottom of the block to improve lower structure rigidity. The single-piece oil sump is also of a pressed aluminum construction. The cylinder head and the camshaft bearing housing are manufactured from cast aluminum. The exhaust manifolds are of a fabricated stainless steel twin skin design incorporating catalytic converters and a moulded plastic acoustic cover is fitted over the upper engine to reduce engine-generated noise.
Engine Structure
Technical features
The engines technical features include:
- A 6-cylinder, inline configuration, liquid cooled, aluminium cylinder block with cast iron liners
- Pistons are cast from a light alloy metal, with 2 compression rings and a 3-piece oil control ring
- Aluminum cylinder head, incorporating 2 camshafts
- Four valves per cylinder
- Variable lift height hydraulic valve tappets (intake only)
- Variable Camshaft Timing (VCT) (intake only)
- Crankshaft vibration damper to give the crankshaft a smoother operation
- A single gear driven camshaft timing chain drives both camshafts
- An aluminum bedplate section between the oil pan and cylinder block
- A forged steel crankshaft with induction hardened bearing surfaces
- Forged steel connecting rods
- A Rear End Ancillary Drive (READ) system
- Two fabricated stainless steel twin skin exhaust manifolds
- A 3-position Variable Intake System (VIS)
- An advanced Engine Management System (EMS) incorporating electronic throttle control
- Four catalytic converters
Technical data
CYLINDER BLOCK COMPONENTS
The main cylinder block components are:
- Cylinder block
- Connecting rods and pistons
- Piston cooling jets
- Generator
- Gear housing
- Thermostat housing
- Crankshaft Position (CKP) sensor
- Knock sensors
- Coolant pump
- Coolant inlet pipe
Cylinder Block
The cylinders and crankcase are contained in the cylinder block, which is of a cast aluminum construction. The cylinder sleeves are made of cast iron and cast in bores. The cylinder block is of a pen coolant mantle design, which allows coolant to flow freely around the upper section of the cylinders.
Connecting rods and Pistons
The connecting rods are 'L' profile forged with a trapezium shaped (a shape with 4 sides with 2 of its sides parallel) small end. The big end has a fracture split bearing cap, which gives a stable joint because the bearing cap and connecting rod are secured in the actual fracture surface. Aluminium bearings are used for both the lower and upper bearing half.
The pistons are cast from a light-alloy metal consisting of aluminium and silicon. The piston skirt is graphite coated at the front and rear to ensure low friction between the piston and cylinder, particularly during cold starting and during short periods of extreme load. The piston is 'weight optimized', which means, for example, that the piston pin is comparatively short and that the piston is missing material from the sides.
Each piston has 3 piston rings:
- An upper compression ring of nitrated steel
- A second ring of alloyed cast iron, which functions as both a compression ring and an oil scraper ring
- A 3-part oil ring made of nitrated steel
Piston Cooling Jets
Jets located in the cylinder block spray oil on to the inside of the piston to provide piston and piston pin lubrication and cooling. The oil is distributed through the cylinder block, via the main oil gallery and channels bored in the block.
Generator
The generator is located at the rear of the intake side of the cylinder block. The generator is driven by the crankshaft gearwheel via the auxiliary unit shaft gearwheel and the auxiliary unit inner shaft gear wheel (see gear housing section for more information).
Gear Housing Components
The gear housing functions as an external cover for the following sub-sections:
- Intermediate shaft
- Camshaft drive outer shaft
- Auxiliary unit inner shaft
Intermediate Shaft
The intermediate shaft is used to locate the camshaft drive shaft gear wheel in the cylinder block. The shaft is journaled with a double conical roller bearing. The auxiliary unit shaft drive gear wheel is in 2 pieces, with the narrow half being spring tensioned in the opposite direction to the wide half. This feature reduces noise because gear play is eliminated. Only the wide half drives the auxiliary unit's gear wheel. The camshaft chain gear wheel is of the conventional design.
The shaft is sealed against the exhaust side (i.e. the rear side of the cylinder block) by a sealing washer. To remove or install the washer, the flywheel/flexplate must be removed.
Camshaft Drive Outer Shaft
The camshaft drive outer shaft is journaled at the front end of the shaft with a double row bearing in the gear housing. Needle bearings are used at the rear end (pulley side) against the auxiliary unit shaft. The camshaft drive outer shaft gear wheel is in 2 pieces, a wide and a narrow half to reduce noise. The camshaft chain gear wheel is also located on the shaft and is used to drive the camshafts chain.
Auxiliary Unit Inner Shaft
The auxiliary unit inner shaft is journaled at the front end of the shaft (generator side) in the gear housing with a single row bearing. Needle bearings are used at the rear end (pulley side) against the camshaft drive shaft. There is a pulley at the rear end of the shaft that drives the Air Conditioning (AC) compressor and the power steering pump, via a polyvee belt. The shaft also drives the generator at the front end, via a sleeve connector.
Thermostat Housing
The thermostat housing is located towards the front of the intake side of the engine cylinder block. The housing contains a wax type thermostat and a coolant temperature sensor.
Coolant flows in at the coolant pump and passes through a number of channels before it collects and then flows out to the thermostat housing. If the thermostat housing is closed, the coolant passes via the by-pass channel directly to the coolant pump to then circulate through the cylinder block again For additional information, refer to Engine Cooling - 3.2L Description and Operation.
Crankshaft Position Sensor
The Crankshaft Position (CKP) sensor is located at the rear of the intake side of the cylinder block. The sensor provides an input of engine crankshaft speed and position. The sensor works on the principle of the Hall effect and scans a trigger wheel (magnetic disc) on the flywheel For additional information, refer to Electronic Engine Controls - 3.2L Electronic Engine Controls.
Knock Sensors
The knock sensors are located at the front and rear intake side of the cylinder block. They are piezo-electric sensors that provide inputs to detect and locate detonation during combustion For additional information, refer to Electronic Engine Controls - 3.2L Electronic Engine Controls.
Coolant Pump
The coolant pump is installed on the RH side of the cylinder block rear face and is secured and sealed via 6 bolts and an 'O' ring. The coolant pump and power steering pump are both driven by a single pulley via a poly-vee belt. A keyed shaft at the front of the pulley drives the power steering pump, while a driver mechanism attached to the rear of the pulley drives the coolant pump.
Coolant Inlet Pipe
The coolant inlet pipe is located on the exhaust side of the engine. The coolant is routed from the coolant pump into 2 connections on the engine block via the coolant inlet pipe and leaves the engine block at the rear end, via the thermostat housing.
CYLINDER HEAD COMPONENTS
The main cylinder head components are:
- Cylinder head
- Cylinder head gasket
- Oil separator
- Camshaft housing
- Camshafts
- Intake and exhaust valve assemblies
- Variable Camshaft Timing (VCT) solenoid and Camshaft Position (CMP) sensors
- Spark plugs
- Coils
- Fuel rail and injectors
- Vacuum pump
- Intake manifold
- Exhaust manifold
Cylinder Head
The chill cast cylinder head is of the cross-flow type, manufactured from a light-alloy metal. Deep-seated bolts, to reduce distortion, secure the cylinder head to the cylinder block. Two hollow locating dowels align the cylinder head with the cylinder block. The 2 camshafts are supported by 7 bearing caps each, directly in the cylinder head and camshaft cover.
Cylinder Head Gasket
The seal between the cylinder head and cylinder block is a conventional cylinder head gasket. The head gasket is made of steel and has multiple layers. For service, there is only 1 size of gasket available.
Oil Separation Housing
Crankcase gases are routed from the crankcase, engine block and cylinder head to the oil separation housing located on the camshaft cover. From the oil separation housing, the crankcase gases are routed via a pressure regulator, located at the rear edge of the housing, to the cylinder head and the intake ports for the intake valves. For additional information, refer to Evaporative Emissions Description and Operation
Camshaft Housing
The chill cast camshaft housing is manufactured from a light-alloy metal and acts as a combined valve cover and camshaft bearing cap. The housing has cast oil ducts on it's underside, which ensure good oil supply to the camshafts and the valve lifters. The oil separation housing is located on the camshaft cover For additional information, refer to Engine Emission Control - 3.2L .
Camshafts
The camshafts are of a hollow steel tube construction, drilled to save weight. Each camshaft is retained in the cylinder head by the camshaft housing. The intake camshaft is equipped with a VCT unit and also drives the vacuum pump.
The intake camshaft has cam lobes with different profiles. One for a small lifting height of 3.6 mm, and 1 for larger lifting height of 10.0 mm. The transition between the lifting heights is controlled via the Camshaft Profile Switching (CPS) function.
The exhaust camshaft is conventional, i.e. only has a lifting height of 10.0 mm.
Intake and Exhaust Valve Assemblies
The cylinder head incorporates 2 overhead camshafts operating 4 valves per cylinder via hydraulic tappets for the intake camshaft and mechanical tappets for the exhaust camshaft.
Camshaft Profile Switching
CPS is a system where the intake valves, at engine speeds up to approximately 3000 rpm, have a small lifting height of 3.6 mm, and at speeds above approximately 3000 rpm, have a greater lifting height of 10.0 mm. CPS, in combination with the VCT function makes it possible to control the cylinders' incoming air quantity in such a way that the Electronic Throttle Actuator (ETA) can be fully open. A fully open ETA, during operation, reduces the pump losses considerably compared with when the amount of intake air is controlled by the ETA itself. Reduced pump losses, in turn, cause a reduction in fuel consumption.
The electrical hydraulic valves are seat valves.
The valves have 3 inputs/outputs:
- Inlet, oil supply
- To/from tappet
- To return, i.e. oil pan
A solenoid is affected via an electro-magnet, which affects a valve that can assume 2 positions.
When the solenoid is not activated, the valve is only affected by the oil pressure on the intake side. The valve closes for intake but opens between the tappet and return.
The oil pressure is low at the tappet's outer locking pin and the valves lift a small amount.
When the solenoid is activated, the valve is affected from above by an electro-magnet that overpowers the force of the oil pressure.
The valve shifts position and closes between the tappet and return but opens the connections between intake and tappet.
The oil pressure is high at the tappet's outer locking pin that is lifted and affects the inner locking pin. Outer and inner tappet connect and the valves lift a greater amount.
The intake camshaft is equipped with 3 lobes for each valve. One centrally located with a small lifting height of 3.6 mm, and 2 outer lobes with greater (same) lifting heights of 10.0 mm.
At small lifting heights, only the centrally located lobe works on the valve, which occurs via the inner tappet. The outer lobes work on the outer tappet that follows the movement of the lobes. The return spring is compressed and ensures that the tappet is always in contact with the camshaft. When the centrally located tappet and the outer tappet are not joined, the outer tappet moves without affecting the valve. Thus the lifting height is small. At high lifting height, the inner tappet and the outer tappet are joined via the 2 lock pins.
The position of the lock pins is controlled hydraulically by 2 electro-hydraulic CPS solenoid valves. These valves are located in the camshaft housing.
One solenoid controls the valves for cylinders 1, 2 and 4 whilst the other controls the valves for cylinders 3, 5 and 6. The solenoids therefore control 6 valves each (when the engine has 2 intake valves and 2 exhaust valves per cylinder).
The position of the solenoids valves, on or off, are controlled by the ECM For additional information, refer to Electronic Engine Controls - 3.2L Electronic Engine Controls.
The inner tappet works like a hydraulic tappet, which compensates for any wear. The valve clearance is therefore '0'.
The exhaust camshaft is conventional and has a lifting height of 10.0 mm. The tappets are mechanical (i.e. have valve clearance).
Camshaft Data
Intake
- Opening angle, 3.6, mm lifting height:
- Crankshaft degrees - 152°
- Crankshaft degrees - 76°
- Opening angle, 10.0 mm lifting height:
- Crankshaft degrees - 240°
- Crankshaft degrees - 120°
Exhaust
- Opening angle, 10.0 mm lifting height:
- Crankshaft degrees - 240°
- Crankshaft degrees - 120°
The intake camshaft has a VCT unit.
- BTDC = Before Top Dead Centre
- ABDC = After Bottom Dead Centre
- BBDC = Before Bottom Dead Centre
- ATDC = After Top Dead Centre
Camshaft Position in Relation to Load and RPM
By closing the intake valves early at low load and low engine speed, reduced fuel consumption is achieved.
The oil inlet, located on the front edge of the cylinder, supplies oil to the following:
- The hydraulic tappets
- The vacuum pump
- The nozzle for cam chain lubrication
- The intake camshaft's front bearing
- The electro-hydraulic CPS solenoid valves, front and rear
- The tappets with CPS function
There is a bleed valve (16) in the duct for the rear electro-hydraulic solenoid valves.
The duct is also equipped with 2 calibrated passages (3) to each tappet circuit (2) (i.e. the circuits after the CPS solenoid valves). A continuous flow through the circuit ensures the necessary stable pressure differences that are necessary for a stable transfer between the small and large tappet (or vice versa).
NOTE:
In the event of a small lifting height, the tappet circuit, in principle, has no pressure when the CPS valves are open, which produces a return flow to the oil pan.
A filter is located in each passage.
The oil inlet, located on the rear edge of the cylinder, supplies oil to the following:
- The camshaft chain's hydraulic tensioner
- The intake camshaft VCT unit
- The intake camshaft's bearings
- The exhaust camshaft's bearings
To switch from low lift to high lift and vice versa as smoothly as possible, the transfer is only permitted when certain conditions are completed. These are:
- That the oil temperature is above +40°C (104°F). Calculated internally in the ECM, from, amongst other things, the coolant temperature
- Occasionally the volumetric efficiency is the same for low and high lift, which means that the air requirement is within a range where it can be managed initially by VCT control. This is to achieve as soft a transfer as possible.
- It is possible to adjust ignition timing to prevent torque peaks during CPS control
For additional information, refer to Electronic Engine Controls - 3.2L Electronic Engine Controls
Variable Camshaft Timing Solenoid and Camshaft Position Sensors
The profile, or position and shape of the camshaft lobes are optimized for a certain engine rpm, but this normally limits low-end torque or high-end power. At high engine speeds, an engine requires large amounts of air. However, the intake valves may close before all the air has been given a chance to flow in. On the other hand, if the camshaft keeps the valves open for longer periods of time, problems start to occur at the lower engine speeds. This will cause unburnt fuel to exit the engine since the valves are still open.
To overcome this, VCT changes the valve timing by either advancing or retarding the camshafts to allow for optimum engine performance, reduced emissions, and increased fuel efficiency. This is achieved via an electronically controlled hydraulic solenoid valve located in the camshaft housing at the rear of the engine, behind the rear CPS solenoid. The ECM transmits a signal to the solenoid, which directs engine oil into the VCT unit. A valve spool in the VCT unit regulates the flow of oil. For additional information, refer to Electronic Engine Controls - 3.2L Electronic Engine Controls.
There are 2 CMP sensors located in the camshaft housing. The CMP sensors monitor the position of the camshafts to establish ignition timing order, fuel injection triggering and for accurate VCT camshaft advance-retard timing feedback.
The CMP sensor is a Hall-effect sensor, which switches a battery fed supply on and off. The supply is switched when the teeth of the reluctor pass by the tip of the sensor. The 4 teeth are of differing shapes, so the ECM can determine the exact position of the camshaft at any time. For additional information, refer to Electronic Engine Controls - 3.2L Electronic Engine Controls
Spark Plugs
The spark plugs screw into the cylinder head through the camshaft housing and are controlled by the ECM via individual coils.
Ignition Coils
The ECM uses a separate ignition coil for each spark plug. The ignition coils are of the plug top design, which attach to the top of the spark plug. The coils are secured to the camshaft housing with a bolt.
The coil has a rubber seal, which seals the coil in the spark plug hole in the cylinder head, preventing the ingress of moisture and debris around the spark plug. These coils eliminate the requirement for HT leads, which in turn improves the ignition system reliability.
Each coil has a 3-pin female connector, which provide for a battery voltage ignition feed, an earth for the secondary winding and a primary winding negative (switch) terminal. The switch terminal of each coil is connected to a separate pin on the ECM to allow independent switching. For additional information, refer to Electronic Engine Controls - 3.2L Electronic Engine Controls