The Citroën Xantia V6:
The ES9 J4 is a normally aspirated petrol engine with 60° V6 configuration and four valves per cylinder. It is fitted crosswise in the Xantia engine compartment, together with the gearbox mounted at the end.
From bottom to top, the engine consists of a sheet steel oil pan, topped by a light alloy crankcase, with a light alloy cylinder block. Viewed as a cross-section, each of the branches of the Y-section block is topped by an aluminum alloy cylinder head, each of which holds two camshafts, making four camshafts in all. Each of the two cylinder heads takes two aluminum alloy camshaft castings and each of these is capped by an aluminum alloy cover.
The V configuration motor has two aluminum alloy cylinder heads, each of which is made up of five parts. The cylinder head bases, which fit on the cylinder block, house the combustion chambers, the valve systems, the inlet piping, the water circulation galleries, and the lower half-bearings for the camshafts.
The camshafts are fitted onto the cylinder heads and held in place by the upper half bearings located in the four camshaft casings.
Each of the two cylinder heads holds two opposing camshafts, one operating the inlet valves and the other the exhaust vales. The frontmost inlet camshaft casing holds the engine oil-fill orifice.
The spark plugs protrude through the combustion chamber roofs in the cylinder head, about 3 mm off-centre toward the exhaust valve side. The cylinder head / cylinder block assembly are specially shaped to ensure efficient fuel-air mix for optimum combustion.
The cylinder block is of a new design. Made of aluminum alloy with cast-iron sleeves, it has an individual bore for each cylinder.
Note: This new type of cylinder block has no lengthwise opening for the cylinder sleeves, when seen from above. Instead, the cylinder sleeves are fitted in special bores to give a stiffer assembly.
The steel crankshaft, with six offset crankpins, is borne on four bearings and balanced by means of five counterweights. It is meshed for increased stiffness and strength, while the grooves of the pivots and crankpins have a partial imprint. At one end, it carries a six-V-slot pulley with torsion vibration damper for driving the accessories and a distribution pinion for driving the camshaft and water pump.
The crankshaft is held in place on the cylinder block by means of an aluminum alloy crankcase. This is cast using a special technology in order to integrate cast iron inserts, which greatly reduce vibration and thus improve vehicle acoustics.
The crankshaft bearings are in aluminum-tin alloy.
The conrods, in shot-blasted forged steel, have bored head squirter channels, from which pressurised oil is projected onto the piston sleeves at a precise moment for lubrication purposes. The conrod bearings are in copper-lead alloy.
The aluminum alloy pistons have a low-inertia short-skirt design, with flat heads featuring four shallow valve clearance recesses. The advanced piston design is the fruit of extensive development work on a Cray supercomputer.
The very high compression ratio of 10.5/1 ensures excellent engine efficiency.
Distribution is performed by four overhead camshafts, two per cylinder head. One camshaft on each cylinder head operates the inlet valves and the other exhaust valves. The camshafts are driven by a 32 mm wide belts that also drives the water pump. Three rollers ensure smooth operation, while a dynamic tensor keeps the belt optimally taut. Belt replacement is only required after 160,000 km.
Distribution timing, always a highly complex operation on this type of engine, is facilitated by special pins to set the camshafts and crankshaft.
The camshafts activate the valves via self-adjusting hydraulic tappets.
The inner surface of the tappets is optimised to eliminate play, which could otherwise cause noise on engine start-up.
The distribution casing, in synthetic material, is specially designed to further reduce distribution noise. It is made up of five partially overlapping parts, joined by silicon foam seals.
The distribution order is 1-6-3-5-2-4.
|Air & Fuel Intake|
The air intake system was specially designed to allow an excellent response at all engine speeds, with high torque output right down to 2,000 rpm.
The system consists of a two-part intake distributor in aluminum alloy, with six pipes. The two compartments are joined via two permanent links, one long and one short. The dimensions of these links are optimised to produce a change in intake behaviour with engine speed. At low engine speeds, the two chambers behave as separate compartments (V1 and V2) which are effectively to generate the required torque. At high engine speeds, the two chambers behave as a single compartment, to ensure a high power output.
Low fuel consumption, a major design criterion for this electronic injection engine, was sought by minimising friction and by optimising the fuel intake system. The engine is tuned to give optimum performance with RON 98 petrol. However, thanks to a built-in knocking detection function the engine will also work satisfactorily with RON 95 fuel, despite the very high compression ratio (10.5/1).
The engine uses a new-generation Bosch MP 7.0 Motronic engine control unit, which offers very high computation power. The engine control functions input data on engine speed and air pressure. Semi-sequential injection works by groups of two cylinders at a time, with two injections and two sparks on each engine cycle (cylinders 1 and 5, 2 and 6, 3 and 4).
A number of special controller functions contribute directly to improving the engine response:
The engine uses twin static ignition coils controlled by a Bosch Mp. 7.0 Motronic computer. Ignition works two cylinders at a time, with two sparks per cycle (one spark being ineffective). Ignition is fired by a Sagem BBC3.2 compact coil unit, which contains three coils, one for each set of two spark plugs.
|Exhaust / Pollution Control System|
The engine unit is fitted with two identical cast iron manifolds, one on the front and one on the rear. The front part of the exhaust system is preheated by hot air in order to stimulate fast catalysis action. The three-way catalytic converter, with a capacity of 3.3 litres, takes the form of two ceramic blocks.
|Engine Mounting System|
The pendular engine mounting system, with its two anti-torque stay rods, is specially designed to prevent swing motion in the power unit at the engine's low idle speed or 650 rpm. This speed was adopted to minimise fuel consumption.
The Xantia V6 features an upgraded braking system. The front and rear discs are wider; the front discs are thicker; the rear brake linings have a larger surface area; the front discs are ventilated; and four-sensor ABS is fitted as standard.
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