02.12.2003

Record-breaking power units and suspension


The true heart and soul of every Alfa Romeo model is its engine. The Alfa cars' attractive, personality-packed looks conceal a diverse range of outstanding high-tech power units that offer generous performance. To allow visitors to examine them in detail, Alfa has prepared four aluminium, glass and Plexiglas show chambers that house the same number of engines. Firstly, the brand new 2.4 JTD 5 cylinder Multijet 20v delivering 129 kW (175 bhp) and 385 Nm (39.3 kgm) of torque and the 103 kW (140 bhp), 1.9 JTD Multijet 16v, both members of the latest generation of Common Rail power units, multivalve JTD engines featuring Multijet technology.
So much for the turbodiesels. But Alfa Romeo also leads the field when it comes to petrol engines. Just for starts, a 121 kW (165 bhp) 2.0 JTS available with Selespeed transmission, the first direct injection petrol engine with a specific power output of 61.4 kW/l (83.8 bhp/l). Due to its slightly modified gear ratio, the 2.0 JTS offers greater verve to place more emphasis on driving satisfaction. The 2.0 JTS is a top-performing power unit that owes its name of JTS (Jet Thrust Stoichiometric) to its specific combustion system.
This is joined by the 24 valve 3.2 V6, the powerful unit adopted on Alfa 147, 156 and Sportwagon in the GTA family and, a few months ago, also on the New Alfa GTV and Spider. This gem of automotive engineering develops a power output of 184 kW (250 bhp) at 6200 rpm with a maximum torque of 300 Nm (30.6 kgm) at 4800 rpm (on the GTV and Spider, the power output is 240 bhp and torque is 289 Nm).
The fifth showcase displays the sophisticated high double wishbone suspension fitted to GTA versions.


The Multijet system, secret of second generation JTD engines

The underlying principles of second generation turbodiesel engines remain the same, i.e. high injection pressure and electronic injector control. With one extra feature: during each engine cycle, the number of injections increases over and above the current number of two. In this way, the same amount of diesel is burnt inside the cylinder but in several portions to achieve smoother combustion.
The advantages include lower running noise, reduced emissions and a 6-7% increase in performance. All this comes with a level of engine efficiency that improves car handling still further.
These results are not to be sneezed at, particularly because they are obtained with an engine that represents an incredible leap forward from prechamber diesels and even improves on first generation JTD engines.
The secret of the Multijet engine lies in the control unit that governs the electric injector opening and closure system (and also in the injectors themselves). The crucial element is the electronic control unit itself that can perform a set of injections that may be very closely spaced.
Fiat Auto's researchers developed the part (together with the injectors) specially for this application. It is designed to deliver the multiple injections that assure the designer more accurate control of pressures and temperatures developed inside the combustion chamber and also more efficient use of air taken into the cylinders.
This enables further goals to be achieved: quieter combustion, reduced emissions and improved performance. The Multijet system is underpinned by long years of research. Our engineers began by resolving the problem of limits imposed by the control units. Then they went on to map the benefits they could achieve by plotting different multiple injection sequences (two secondary injections very close to the main injection; one secondary injection not too close to the main injection plus two closely-spaced secondary injections; one secondary injection and then two main injections close together after a certain period etc.) against different engine service conditions: in the idling region; with low loads and low rpm; with high rpm and moderate load; with low rpm and high load etc.
The study revealed the potential of the system and showed that great benefits are achievable in all cases, though these tend to focus on one field or another according to the type of sequence chosen and the engine service area targeted. In some cases, for example, the priority is to reduce start-up times and fume levels, in other cases it is to increase torque and reduce noise while in others it is to reduce emissions and ensure a quieter drive.
And now this research strand has led to the creation of Multijet engines: another first for the Fiat Group in the diesel engine field. All this was possible because we have been building up know-how in this field since 1986, the date that marked the arrival of the Croma TDI, the first direct injection diesel vehicle in the world.
At that time, this represented a true engineering breakthrough that was later adopted by other manufacturers. Direct diesel injection engines offered better performance and lower fuel consumption but failed to resolve the problem of excessive engine noise at low rpms and while speeding up or slowing down. So work began on a more advanced direct injection system and a few years later this led to the development of the Common Rail principle and the Unijet system.
The idea first came from the Zurich University research laboratories where scientists were working on an injection system that had never before been applied to a vehicle, i.e. the Common Rail system. The idea is simple yet revolutionary. If you continue to push diesel into a tank, the pressure inside will rise and the tank itself will become a hydraulic accumulator (or rail), i.e. a reserve of pressurised fuel ready for use.
Three years later, in 1990, the Unijet system developed by Magneti Marelli, Fiat Research Centre and Elasis on the Common Rail principle entered the pre-production stage. This stage was completed in 1994, when Fiat Auto started to look for a partner with special knowledge of diesel engine injection systems. The final stage of the project, i.e. completion of development and industrial production, was eventually entrusted to the Robert Bosch company.
Now our story has reached 1997 and the launch date of the Alfa 156 JTD with its revolutionary turbodiesel engine. Compared to conventional diesel units, the JTD guarantees an average improvement in performance of 12% together with a 15% reduction in fuel consumption. These results meant that cars fitted with the engine were an immediate hit.
Now the time is ripe for the second generation of JTD engines, the Multijet and multivalve units: in 2002 with the 1.9 JTD Multijet 16v (the forerunner of this new multiple injection family), today with the 129 kW (175 bhp) 2.4 JTD Multijet 20v.


The 129 kW (175 bhp) 2.4 JTD Multijet 20v

The powerful 5-cylinder 129 kW (175 bhp) 2.4 JTD Multijet 20v, the second engine in the JTD multivalve family with Multijet technology and available on the new Alfa 156, Sportwagon and Alfa 166 models.
This brand-new unit offers various benefits. The engine is quieter as it warms up. The improvement can be quantified as a reduction of 3 to 6 decibels depending on engine speed and environmental temperature. Then, great power (175 bhp - 129 kW at 4000 rpm + 25 bhp compared to the 2.4 JTD 10 valve) and generous torque (385 Nm - 39.3 kgm at 2000 rpm against the 305 Nm at 1800 rpm of the 2.4 JTD 10v). The weight/power ratio is 7.9 kg/bhp, a figure that confirms the true sporting soul of this 2.4 JTD Multijet-powered car. Higher performance compared to the 2.4 JTD 10v with unvaried fuel consumption. The new 2.4 JTD Multijet 20v also reduces emissions even though it is not fitted with sophisticated exhaust gas treatment devices.
The new engine is derived from the tried and tested 2.4 JTD 10 valve Common Rail unit and takes the form of a five cylinder in line unit with bore of 82 millimetres and stroke of 90.4 millimetres. The four valves per cylinder are driven directly by a twin overhead camshaft via hydraulic tappets and rocker arms. The new turbodiesel has undergone several engineering changes to increase performance and engine torque at low speeds and to reduce noise levels and vibration.
For example, the Common Rail system used on the 20 valve 2.4 JTD Multijet unit includes two new strategies for automatically calibrating and balancing the diesel injected to lower noise and reduce vibration.
Certain engine components are brand new: a cylinder head with hydraulic tappets, steel connecting rods and crankshaft, a piston with an internal channel to carry cooling oil to the main and connecting rod bearings that are made out of different material to the previous unit. The exhaust and intake manifolds are also new: the former is made out of a special high-strength material while the latter is made out of pressure cast aluminium.
The electronically-controlled EGR system is cooled by exhaust gas. The lubrication circuit has a new oil pump and an external heat exchanger (air/oil) for cooling the oil. The cooling system is fitted with a different water pump. This long series of improvements and changes have created a reliable, powerful engine with low fuel consumption.
These results have been achieved by adopting a new engine setting, increasing the direct injection pressure from 1350 to 1400 bars and introducing a new turbocharger setting.
The power units are turbocharged via a Garrett turbocharger with variable geometry turbine that helps improve power delivery by allowing very high torque delivery even at low rpms. Suffice it to say that 90% of maximum torque is available between 1750 and 3500 rpm. These data translate into great driving satisfaction and truly inspiring performance - on both the Alfa 156 and the Sportwagon. The Alfa 156 reaches a top speed of 225 km/h (on the circuit) and accelerates from 0 to 100 km/h in 8.3 seconds. The Sportwagon takes just 8.6 seconds to speed from 0 to 100 km/h. With very low fuel consumption figures all round: combined cycle 6.6 l/100 km, urban cycle 8.8, extra-urban cycle 5.3. The figures recorded by the Sportwagon are respectively 6.7 l/100 km, 8.9 l/100 km and 5.5 l/100 km.
Finally, the new 129 kW (175 bhp) 2.4 JTD Multijet 20v fits a new 6-speed manual gearbox. The 3-axle device is more compact than the present one and presents synchronised reverse and a clutch with automatic wear take-up.


The 103 kW (140 bhp) 1.9 JTD Multijet 16v

At the end of 2002, Alfa Romeo introduced its 103 kW (140 bhp) 1.9 JTD Multijet 16v, the first of the second generation of Common Rail engines in the world. Now it has been adopted by the new 156 and Sportwagon, the Alfa 147 and Alfa GT (boosted to 150 bhp) in combination with a 6-speed gearbox with a sports configuration.
The unit is a 4 cylinder in line engine with a bore of 82 millimetres and a stroke of 90.4 mm, capable of delivering a power output of 103 kW at 4000 rpm and a torque of 305 Nm (31 kgm) at 2000 rpm.
The advantages and qualities are as described for the 2.4 JTD Multijet 20v, because this turbodiesel has also undergone various technical improvements to increase performance and engine torque at low speeds and to reduce noise and vibrations.
For example, the Common Rail system used on the 1.9 JTD Multijet 16v unit includes two new strategies for automatically calibrating and balancing the diesel injected to lower noise and reduce vibration.


122 kW (165 bhp) 2.0 JTS

Here is the first direct injection petrol engine with a specific power of 61.9 kW/l (83.8 bhp/l). Due to its slightly modified gear ratio, the 2.0 JTS offers greater verve to place more emphasis on driving satisfaction. An ultra-high performance power unit that takes the name of JTS (Jet Thrust Stoichiometric) from its specific combustion system, an acronym that is destined to identify an entire family of future Alfa Romeo engines.
As far as the customer is concerned, this means an aspirated two litre car that:

  • already meets the tough Euro 4 emission limits;
  • does not need low sulphur petrol but is able to use the normal petrol already on sale in Europe and the United States.

    Alfa Romeo (and indeed Fiat Auto) is fitting its new models with its first petrol engine with injectors that inject directly into the combustion chamber. It achieves its end by interpreting the principles of stratified charge and the creation of motion in the mixture inside the cylinder in an entirely original way.

    - Lean burn, but not too lean
    The possibility of injecting petrol directly into the combustion chamber instead of the intake duct has been known since Nikolaus Otto (who took out a patent in 1877) and has been applied for two different purposes over the years. On racing cars in the Fifties and Sixties to increase engine power. More recently (since 1996), to reduce fuel consumption.
    Recently, manufacturers have devoted all their efforts in this latter direction and gratifying results have been achieved with the stratified charge method. The principle is simple: instead of injecting all the petrol required to maintain the normal air-fuel ratio of 14.7:1 (stoichiometric) throughout the combustion chamber, only a small amount of fuel is injected that mixes with the air to form a core of almost stoichiometric composition about the spark plug. The resulting mixture is stratified or layered because it is richer where the ignition spark ignites and increasingly lean (more air and less fuel) as it approaches the outside of the chamber.
    So far the benefits of this lean burn system, usually applied in the rpm band up to 3000 rpm, have amounted to a fuel saving of some 10%. The disadvantages may be summarised as follows:

  • a drop in performance when the car is required to deliver full power (because the ducts and pistons are shaped in a certain way that is essential to reduce fuel consumption at low speeds);
  • the need to use sulphur-free fuel that is difficult to find in Europe and practically unknown in the US;
  • the requirement for costly, delicate exhaust gas treatment methods (DENox) to reduce the higher nitrogen oxide emissions generated by the leaner burn.

    It goes without saying that Alfa Romeo's approach to the new technology had to be quite different. Category-topping performance and irrepressible driving behaviour have always been essential requirements for all Brand models.
    But what was to stop us from using direct injection to increase engine power and torque in keeping with the sporty applications of this technology.
    Then, we reasoned, we could bring in the stratified charge system to reduce fuel consumption within a restricted rpm band around idle speed.
    The result was an entirely original Alfa Romeo approach to applying direct injection in petrol engines. A solution that offered a compromise between the two methods pursued to date. The New Alfa 156 2.0 JTS works using a lean burn approach up to around 1500 rpm and this saves fuel, although not as much as on other lean GDIs. Above this rpm, the engine burns a stoichiometric air-fuel mixture, i.e. with a normal 14.7:1 ratio between both components. All this means outstanding performance. Much better than would be obtained using a normal indirect injection petrol unit.
    Firstly, because petrol injected directly into the combustion chamber instead of the duct cools intake air to increase the engine's volumetric efficiency. As temperature drops, the gases increase in density and their volume therefore decreases: this means that more air can be introduced into the combustion chamber.
    Power unit susceptibility to knock is also reduced by chamber cooling. It is therefore possible to increase the compression ratio - in this case from 10:1 for the 2.0 T. Spark to 11.3:1 for the 2.0 JTS.
    This means more power for the new Alfa Romeo engine that is, moreover, able to deliver its power unhindered because the exhaust gas treatment system used on the 156 does not generate the strong counterpressures typical of the Nox absorbers used by lean-burn GDIs.
    Direct introduction of petrol into the chamber improves power unit response speed to the accelerator control (it is faster overall than a conventional petrol engine).

    - Benefits: higher performance and lower fuel consumption
    Compared to the 2.0 T. Spark unit, the 2.0 JTS unit fitted to the New Alfa 156 offers slightly lower fuel consumption and a generous increase in power and above all torque: +15 bhp and +26 Nm. And all this is achieved using petrol currently on sale and current catalytic converters.
    In detail, the New 156 equipped with the 2.0 JTS reaches a top speed of 220 km/h (on the circuit) and goes from 0 to 100 km/h in 8.2 seconds (the Sportwagon records the same figures). The saloon consumes 8.6 l/100 km (combined cycle), 6.6 (extra-urban cycle) and 12.2 (urban cycle). Sportwagon fuel consumption is slightly higher, respectively: 8.9 - 6.8 - 12.5.

    - A new combustion chamber principle
    The new JTS combustion system displays two distinctive features:

  • the principle followed to generate the movement that propels the air and fuel mixture toward the spark plug inside the cylinder;
  • the range of rotation speeds within which the engine works using a lean burn system.

    Let's take a look at the first point. In other GDI engines, the air's force drags the fuel spray into the area where the ignition spark ignites. This option is determined by a desire to achieve a very lean mixture (up to 60:1) and thus noteworthy fuel savings. But it brings a need to change the air's motion within the combustion chamber (charge motion) according to rpm level and this complicates the air input mechanisms (throttles, duct closure systems etc.).
    On the 2.0 JTS, however, the force of the fuel spray (Jet Thrust) propels the fuel toward the spark plug as it mixes with the air. In this way, we achieve a charge that is less lean overall (the ratio remains constant at all speeds and is 25:1) and less fuel is saved as a result. But the engine's internal mechanism is far less complicated because it lacks systems for altering the air's motion.
    The same process of simplification also guarantees the limitation of lean burn technology to rpm levels around idle speed (up to 1500 rpm). GDI engines that use stratified charge within a broader speed band (up to 3000 rpm) must employ modified piston and duct profiles. The resulting shape does not allow power to be optimised at high speeds.
    The use of stratified charge only up to 1500 rpm, however, means that the pistons and ducts on the Alfa Romeo 2.0 JTS are hardly altered. Because their shape is more similar to those of current indirect injection engines, they are able to exploit all available power at high speeds.
    The addition of an exhaust gas treatment system (Nox absorber) to remote nitrogen oxides is also only required when the lean burn range is extended up to 3000 rpm. This also dictates the use of sulphur-free fuel, i.e. the only type that will not damage the catalytic converter.
    The use of stratified charge only at speeds around idle speed, however, allows the 2.0 JTS unit to use a conventional catalytic converter system. This result is also made possible by a more extensive use of exhaust gas recirculation, which reduces the production of nitrogen oxides (NOx). Because Alfa Romeo engines are fitted with variable valve timing, exhaust gas is recirculated to the intake on the 2.0 JTS directly between the intake and exhaust valves (internal EGR).

    - Engineering: what changes
    The main engineering changes on the 2.0 JTS compared to the corresponding Twin Spark engine affect the cylinder head (with Bosch injectors fitted in the chamber), pistons, camshafts and exhaust system. All these components are completely new.
    The intake ports are high performance; the fuel manifold is high pressure (Common Rail type); piston compression ratio is higher - and the exhaust - built to Euro 4 standards - is cascade type.
    The exhaust gas treatment system works conventionally despite an unconventional layout: the system no longer consists of a preconverter and a main converter located under the body. Instead it comprises two main catalytic converters built into the manifold (each connected to a double branch that leads to two cylinders). This frees up the space under the body for a silencer that is more permeable and thus more able to reduce counterpressure for fuller engine power delivery.


    184 kW (250 bhp) 3.2 V6 24v

    This is the heart that beats beneath the bonnet of the Alfa 147, 156, Sportwagon GTA as well as on the newborn Alfa GT and the new Alfa GTV and Spider. This power unit, derived from the now classic V6 24 valve three litre unit, is a vigorous and, above all, 'round' engine. As one expects of a six cylinder engine.
    The engineers changed the crankshaft and pistons on the GTA to increase the cylinder capacity to 3.2 litres and lengthen the stroke to 78 millimetres. This change speaks volumes about the type of performance required because the power could simply have been increased by adjusting the timing, fuel system and electronics.
    The fact that cylinder capacity has been increased by lengthening the stroke means that the aim was not simply to obtain out-and-out performance coupled with high power and torque peaks but also an even, gradual power delivery from the lowest speeds. As befits a car capable of thrilling performance that is suited for driving on ordinary roads as well as on the track.
    The increase in cylinder capacity is naturally accompanied by a whole set of changes. The intake and exhaust ports have been tuned by applying a new timing pattern, the control unit software has been rewritten and the cooling system has been upgraded with the addition of an engine oil radiator.
    The result? Power output is 250 bhp at 6200 rpm with a peak torque of no less than 300 Nm (30.6 kgm) at 4800 rpm. These figures are all it takes to achieve exciting performances and are complemented by a torque curve that permits high values at low speeds. The car can also travel in sixth gear at less than 2000 rpm and unleash speed spurts without changing gear. Extremely satisfying behaviour, therefore, even during daily use. The self-confessed goal of the GTA is this: to offer sensations unique to a racing car yet still be perfectly serviceable for everyday use.
    The transmission has also been reinforced to cope with the upgraded engine. The half-axles are new, while the clutch is bigger and the six-speed gearbox offers new, sturdier components. The manual gearbox may be replaced by a Selespeed version with a Formula 1-derived operating system that makes for swifter gear shifts at low and high speed.
    It should also be emphasised that the Alfa 147 GTA is the fastest and most powerful car in its segment (250 bhp - 184 kW) and delivers thrilling performance: 246 km/h top speed; 6.3 seconds to accelerate from 0 to 100 km/h and 26.1 to cover one kilometre from a standing start. Not to mention spirited responses in terms of dynamism, ride and handling. All the attributes, in fact, that make an Alfa drive differently.
    The 3.2 V6 24 valve unit fitted to the New Alfa GTV develops a power output of 240 bhp at 6200 rpm and boasts a torque curve of 289 Nm at 4800 rpm that allows it to reach 255 km/h. This performance makes it the fastest road car in Alfa Romeo's history.


    The GTA high double wishbone suspension

    Visitors to the Bologna Motor Show can appreciate the sophisticated high double wishbone suspension fitted to 156 and 147 models and also their respective GTA versions. The layout used on the GTA sports saloon is exhibited in a glass case. This meets the ambitious aim of ensuring a driving quality that combines the great control typical of front wheel drive cars with the exceptional sportiness and precision that is so useful over mixed routes.
    The Fiat Research Centre and Fiat Auto Design and Development Department developed a new front suspension specifically for GTA versions. Compared to the suspension adopted on other Alfa models, the system features a reinforced lower beam, special wheel strut with a different steering link fastening position, lower ride, new shock-absorber and spring settings and a bigger diameter antiroll bar.
    All this obtains a more sporty performance from the high double wishbone suspension - known as a quadrilateral suspension because the arms (two overlapping triangles with their bases hinged to the car body and their tips to the wheel unit) create a four-sided figure.
    In geometrical terms, this is the best possible arrangement for reconciling extensive wheel travel with excellent control of tyre working conditions. Because the upper arm is located higher than the wheel centre, this solution allows effective use of the area between wheel and power unit accessories.
    From the structural viewpoint, the device consists of a cast iron lower arm, a steel strut and a light alloy upper arm. The coaxial spring-shock absorber unit is connected to the body via a flexible mount and to the lower arm via a light alloy fork. For reasons of space and structural stiffness, the upper arm is jointed to an aluminium shell (anchored to the body), which acts as a support to the upper spring-shock absorber attachment.
    This type of configuration offers many advantages. The double wishbone geometry adopted on GTA versions:

  • optimises tyre grip; on corners the double wishbone configuration tends to make up for the car's external tilt by recovering the camber. It also reduces yaw while braking by allowing the steering axle to tilt toward the front of the car (caster angle);
  • improves traction even under the most difficult conditions;
  • ensures a self-alignment effect proportional to lateral acceleration while cornering;
  • ensures gradual effort on the steering wheel, which increases gradually up to the grip limit;
  • ensures greater steering precision and sensitivity even with sharp angles (tight, twisting bends); during the suspension damping stage, the wheel diverges slightly and this ensures that the driver's steering action is slightly countered as the car approaches the bend;
  • prevents the front end diving during braking (anti-dive effect). The bases of the two overlapping triangles are tilted toward the front of the car so that the braking force on the tyre tread stretches the suspension;
  • prevents lift during acceleration (anti-lift effect) because the pulling force delivered through the half-axle pair is applied to the wheel centre and compresses the suspension.

    The Alfa Romeo engineers have worked to reduce friction and absorb minor roughness more efficiently by choosing: fluid dynamic bushes to hinge the upper triangle to the shell; split gaskets and bushes in Teflon loaded with fibreglass for the shock absorber stems - plus a Teflon seal for the shock absorber piston.
    Correct stiffness of the quadrilateral hinge bushes and steering arm ensures:

  • great steering precision;
  • good grip on the ground (because the tyre angle in relation to the ground reduces on bends);
  • excellent capacity for stress absorption (and hence comfort) due to the increased longitudinal flexibility of the suspension;
  • excellent directional stability (the wheel pulls back without steering when it meets an obstacle);
  • effective absorption of vertical impact due to optimisation of the upper damper attachment unit to the shell;
  • reduction in steering wheel vibration because the steering arm centre lines contain a flexible element;
  • good stabilising action because the steering arms diverge the wheel on the outside of the corner during over-run.


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