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. But one extra feature has been added: 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 underestimated, 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) especially 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 increased 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 the Multijet engines: another first for the Fiat Group in the diesel engine field. But we had been putting in a lot of hard work behind the scenes 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 complete in 1994, when Fiat Auto started to look for a partner with superlative knowledge of diesel engine injection systems. The final stage of the project, i.e. completion of development and industrial production, was eventually entrusted to Robert Bosch.

Now our story has reached 1997 and the launch date of the Alfa 156 JTD with its revolutionary turbodiesel engine. Compared to conventional diesel power 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 16v M-Jet (forerunner of this new family of multipoint injection engines) in 2003 with the 1.9 upgraded to 150 bhp for the Alfa GT and the 129 kW (175 bhp) 2.4 JTD Multijet 20v available on Alfa 166, Alfa 156 and Sportwagon models. Now comes the turn of the New Alfa 147 to enjoy all the benefits of the 150 bhp 1.9 JTD 16v M-Jet.

'Easy Speed' gearbox

The new robotised 'Easy Speed' gearbox is a development of the current Selespeed unit, now with a more user-friendly interface while still guaranteeing the satisfaction and entertainment of a manual transmission. As on the Selespeed, this system is designed to automate the clutch controls and gear lever of a manual gearbox through an electrohydraulic servo device.

Over and above the benefits of the Selespeed, the new device also offers drivers a particularly intuitive interface. Unlike the Selespeed, the lever is multistable, i.e. it allows the customer to check his position at any time (N Neutral - R Reverse - D Drive).

Two operating modes are available: in Manual mode, the driver engages the gears by means of a lever positioned on the tunnel. In Automatic mode, the electronic system takes control and decides when gear changes are required on the basis of two strategies, the first adjusted for driving comfort (NORMAL) and the second adjusted for a more sporty drive (SPORT).

In detail, this is how the new device works in Manual mode: a simple push on the lever is sufficient to ensure a fast, accurate gear change. Electric pulses from the lever satisfy the driver's gear shift wishes on the basis of commands issued by the control unit that controls the hydraulic kit.

The system operating software screens the above input and uses the information to make gear shifts designed for comfort or a sporty drive in manual or automatic mode with the application of a range of operating strategies. The control unit interprets the customer's requirements by mapping the pedal position and the engine rpm.

A simple lever request to move into a higher gear (by moving the lever toward '+') or lower gear (towards the '-' symbol) under the conditions described above allows the driver to obtain sporty and fast or smooth and comfortable gear shifts. This operating strategy also applies in automatic mode. These aims are achieved by implementing the shift by means of a hydraulic system that manages shift speed for performance or comfort without compromise and always assures maximum system performance.

While in Automatic mode, two different operating strategies are available: NORMAL and SPORT. The first is used for driving comfort while the sports function guarantees effervescent lengthening and shifting under all conditions. With both options, the system stretches to a higher ratio once the rpm level has been reached, when the engine delivers maximum torque or power. The system also detects the road gradient while in this mode: a software algorithm measures the gradient increase and modifies the gear shift point so that the best compromise is always obtained between the driver's needs, the road condition and the vehicle's situation (speed and rpm).

Another specific function of the system is to assess vehicle deceleration and adjust downshifting according to the level of deceleration: while in manual, therefore, the system allows downshifting particularly when the driver wishes to change down to take a bend at speed during a sporty drive. In automatic, on the other hand, it anticipates the driver's will and makes available the most appropriate gear to maintain the required level of comfort or fuel saving.

The ease of interaction with the system and the performance increases assured by the new control strategies make the new robotised gearbox the best possible compromise for people who prefer to drive an automatic but do want to give up the satisfaction and fun of a manual transmission.

Comfort suspension

Another major new feature on the New Alfa 147 is the introduction of a Comfort suspension system. This comes as standard on versions equipped with the 150 bhp 1.9 JTD 16v M-Jet and is an option on the others. The new configuration combines a double wishbone front suspension with a MacPherson layout at the rear that guarantees greater levels of comfort without affecting handling.

The front shock absorbers have therefore been modified, lengthening the rod to 13 mm (against the present 11.5) and the rod guide is in teflon. In addition, the use of these particular shocks has demanded a specific setting at both front and rear (standard production) in order to guarantee the correct suspension timing.

This modification has also affected the architecture of the suspension system and not simply a specific setting with which only a damping effect is obtained. As far as customers are concerned, all these changes mean great stability and ease of control even at the limit of grip. Steering box movements are very smooth and balanced and great comfort is assured under all service and road surface conditions.

The entire range of the new car is fitted as standard with the layout that determined the success of the Alfa 156 and Alfa 147: high double wishbone at the front and a MacPherson strut layout at the rear. Then our engineers set to work to adjust the suspension to the car's specific weight distribution and individual characteristics.

As far as the front wishbone configuration is concerned, the improvement was achieved by introducing a new spring type and setting and by the adoption of a new hollow anti-roll bar. Altogether these changes allow a weight reduction of 1.7 kilograms for the same stiffness and roll qualities.

The result is a compact car with a drive that combines the great control typical of a front wheel drive with the outstanding precision and response of a sports car. The New Alfa 147 offers maximum lateral hold, fast approaches to bends and a very effective, precise steering response. This excellent on-road behaviour is aided by the rear end (a MacPherson configuration with asymmetrical arms benefiting from improved elastokinematic properties) that ensures stability in high speed manoeuvres and agility over mixed routes.