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Thursday, January 24, 2008

Fiat Bravo: In Depth

Engines and gearboxes: extremely enjoyable to drive

Behind its distinctive styling, the Fiat Bravo offers a comprehensive range of excellent engines that feature state-of-the-art engineering and generous performance. The range comprises two Multijet turbodiesel engines (1.9 8v delivering 120 and 1.9 16v delivering 150 bhp) and three petrol engines: a 90 bhp 1.4 16v, and two 1.4 16v turbocharged engines from the new T-JET family, delivering 120 and 150 bhp (which will be available after the launch). Each engine offers different advantages, all of which are exploited in full by being combined with 5 or 6-speed gearboxes, and they stand out for their generosity, their sparkling temperament or their outstanding performance and sophisticated technology. But all the engines are extremely reliable and environment-friendly.

All the engines mounted on the Bravo are manufactured by Fiat Powertrain Technologies, the Group new sector. FPT draws together all the activities in the fields of innovation, research, design and manufacture related to engines and gearboxes for all types of applications: from cars to commercial vehicles, boats and agricultural machinery. With approximately 19,000 employees, 17 plants and 10 research centres in eight different countries, the Sector is one of the world most important organisations in its field. At FPT, approximately 3000 highly specialised technicians focus on the development and engineering of innovative technologies. More than 40 patents are filed each year, confirming the quality and seriousness of this commitment, and making Fiat a huge center of technological excellence and constant innovation.

The new T-JET family

A new family of turbocharged petrol engines, known as the T-JET, will make its debut on the Bravo soon after the launch, featuring outstanding performance, prompt response to the accelerator, low consumption, constructional simplicity, sturdiness and reliability. The new 1.4 16v turbo engine will be available in two versions: the first is more sporty, delivering a maximum of 110 kW (150 bhp) at 5500 rpm, while the second is more of a 'tourer', and delivers 90 kW (120 bhp) at 5000 rpm. Both offer a peak torque of 206 Nm (at 2000 rpm on the 110 kW, and at 1750 rpm on the 90 kW), but 230 Nm (at 3000 rpm on the 110 kW) is available, simply by pressing a key on the facia (the SPORT 150 bhp version). The engine is very elastic, requiring fewer gear changes, for an enjoyable, relaxed driving style, but it will respond assertively if the driver puts his foot down. This is one effect of the low inertia of the turboblower, which makes it possible to obtain top performance by acting on the accelerator, with none of the annoying delays typical of this type of engine. The result is outstanding sportiness combined with fuel economy.

The outstanding reliability of the engines is guaranteed by the hundreds of thousands of kilometres driven by prototypes during the development stage, in addition to thousands of hours of static and dynamic tests on the bench. The first maintenance is programmed after 30,000 km, and there is no need for any intermediate servicing. The oil/water heat exchange guarantees these results. The oil filter is of the environment-friendly type.

The computerised engine control system manages all functions using sophisticated calculation algorithms. The accelerator control is of the 'drive-by-wire' type, without mechanical connections, so that the driver can obtain the relaxed or sporty response he wants from the engine, without wasting energy.

These excellent results have been obtained by painstaking design and development of all the engine components, demanding over 120,000 hours of activity. State-of-the-art computer-assisted design and calculation systems were used, making it possible to simulate the greatest stress caused by the turboblower. All the major components have been re-designed, so that we could describe the engine as completely new. Particular attention was paid to fluid dynamics and combustion, to minimise energy losses and to obtain top performance and low consumption, and the results were guaranteed by sophisticated experimental analysis.

The 90 bhp Fire 1.4 16v engine

This engine is a member of the Fire family, and it has a capacity of 1368 cc, and 4 cylinders in line with a bore of 72 mm and stroke of 84 mm. There are four valves per cylinder, activated directly by 2 overhead camshafts. The engine was developed paying particular attention to performance and to fuel economy, two areas in which the Fiat Bravo leads its class. The merit goes to the volumetric efficiency which has been optimised all through the operating range, thanks to a specific fluid-dynamic development of the entire intake system and the timing. The engine delivers 90 bhp (66 kW at 5500 rpm) and peak torque of 128 Nm (13 kgm at 4500 rpm). With this engine, the Bravo has a top speed of 179 km/h, and accelerates from 0 to 100 km/h in 12.5 seconds. Sparkling performance, in spite of low consumption: 8.7 l/100 km in the urban cycle, 5.6 l/100 km out of town and 6.7 l/100 km in the combined cycle.

A sparkling engine that is sparing on fuel. This has been achieved thanks to the adoption of a throttle valve control system known as 'drive by wire'. The 90 bhp 1.4 engine also adopts a new, 'torque-based' engine control unit, which is the state of the art in this field. Its most interesting feature is that it activates all devices through a single coordinator block, whose basic parameter is the torque demanded by the driver when he puts his foot on the accelerator. Translated into a physical torque value, the various demands (including those of the external systems such as ABS) can be coordinated even before the main engine control parameters have been converted (advance, throttle valve position, injection time, etc.) with the enormous advantage of being able to generate them with great precision and in a very short time. This system exploits a single communications standard between the various systems and functions, whose common 'language' is the engine torque. This makes for a level of driveability superior to that available from current systems, while also reducing polluting emissions.

Other features peculiar to the new 90 bhp 1.4 16v Fire are the optimisation of the compression ratio and the high torque values at low speeds, characteristics that make it possible to limit fuel consumption. This target has also been reached thanks to the calibration of the latest generation engine control unit, which keeps fuel consumption very low, compatible with the requirements of driveability, performance and emissions. A catalytic converter positioned in the engine bay (and welded to the exhaust manifold flange using a new technology) reaches very high temperatures very fast, thus reducing emissions even while the engine is warming up. To minimise the environmental impact, the engine also incorporates a returnless fuel supply system, which eliminates fuel recirculation within the tank, thus reducing vapour formation.

High performance, sparing on fuel and clean: to these winning features the 90 bhp 1.4 16v Fire engine also adds excellent acoustic comfort.

The 120 bhp and 150 bhp 1.9 Multijet

Both have 4 cylinders in line, with two valves per cylinder and four valves per cylinder respectively, a bore of 82 mm and stroke of 90.4 mm; the first delivers 120 bhp (88 kW) at 4000 rpm and torque of 255 Nm at 2000 rpm, while the second delivers 150 bhp (110 kW) at 4000 rpm and torque of 305 Nm at 2000 rpm. Several changes have been made to the engineering of the two engines to boost performance and engine torque at low speeds, and to reduce noise and vibration. For example, the 'Common Rail' system envisages two strategies for automatic control of the calibration and balancing of the injected diesel fuel, improving acoustic and vibrational comfort.

Turbocharging is entrusted to a Garrett VGT 17 turbo, with electronic management of the variable geometry, which improves power delivery while guaranteeing very high torque values even at low engine speeds. For example, 90% of peak torque is available between 1750 and 3250 rpm. This translates into extremely enjoyable driving and excellent performance. The Fiat Bravo equipped with the 120 bhp 1.9 Multijet engine has a top speed of 194 km/h and accelerates from 0 to 100 km/h in 10.5 seconds (with the 150 bhp 1.9 Multijet the top speed is 209 km/h, and 0-100 km/h acceleration takes 9 seconds). Brilliant performance in other words, but fuel consumption remains low: 6.9 l/100 km in the urban cycle, 4.3 l/100 km out of town and 5.3 l/100 km in the combined cycle for the 120 bhp Multijet, while the 150 bhp version returns 7.6 l/100 km for the urban cycle, 4.5 l/100 km out of town and 5.6 l/100 km in the mixed cycle. We should also underline that the 120 bhp 1.9 Multijet achieves an excellent 139 g/km where emissions are concerned.

The second generation turbodiesel engines are still based on the principles of the 'Common Rail'; i.e. high injection pressure and electronic injector control. But the new generation engines have an additional feature: during each engine cycle, the number of injections has been increased from the two that are common today. The same amount of diesel fuel is burned inside the cylinder, but it is burned in portions, producing smoother combustion. The advantages include quieter operation, lower emissions and a 6-7% boost in performance accompanied by engine efficiency that makes the car even easier to drive.

These results are significant, because they have been achieved on an engine which represents an incredible leap forward compared to pre-combustion diesels, and even improves on first generation JTDs.

The secret of the Multijet lies both in the control unit that governs the electric injector opening and closing system and the injectors themselves. The crucial element is the electronic control unit itself, which performs a series of extremely close injections.

The components (and the injectors) were developed by Fiat researchers to do just that; it delivers the multiple injections that guarantee more precise control of the pressures and temperatures generated in the combustion chamber, as well as exploiting the air taken into the cylinders more efficiently. This achieves other goals: lower combustion noise, reduced emissions and boosted performance.

The development of the Multijet system is the outcome of years of research. Initially, the technicians solved the problem of the limits posed by the control units. They then drew a map of the benefits obtained by plotting different multiple injection sequences (two secondary injections very close to the main injection, one secondary not too close to the main injection plus two other close secondaries; one secondary, followed, at a certain interval, by two closely-spaced main injections, etc.) with the various operating ranges of the engine: idling, with low loads and low rev speed; with high revs and a moderate load; with low revs and a high load, and so on.

This analysis revealed the potential of the system, and showed that great benefits are achievable at all times, though they tend to focus on one field or another, depending on the type of sequence chosen and the engine service range targeted. In some cases, the priority is to reduce starting times and fume levels, in others, it is to increase torque and reduce noise, in others still, it is to reduce emissions and noise levels. Today this research has resulted in the development of the Multijet engines.

The two Multijet units are friendly to the environment, incorporating an electronic EGR system which cools the recirculating exhaust gases, and a 'close-coupled' catalytic converter, as well as a particulate trap (DPF), a 'for life' system that abates fine dust and is regenerated without additives. In other words, a long list of improvements and measures to produce a reliable, powerful engine that is sparing on fuel.

All the versions have the hydraulic coaxial clutch release mechanism (CSC) developed for the 1.9 Multijet engine. This device, which does not have external actuators, guarantees greater efficiency of the system during the life of the car and also makes it possible to isolate the noise and vibration produced by the engine. Unlike a hose control, this hydraulic system provides for self-regulation of the worn pedal. The system is also combined with a device that recovers friction plate wear, which maintains the load of the clutch pedal constant throughout the life of the vehicle. The optimisation of the components and the use of innovative materials (plastic, aluminium) has made it possible to reduce the weight by more than 2 kg compared to a conventional hydraulic control.

And last but not least, in line with European directives to protect the environment, only environment-friendly friction materials have been used on all versions, whether petrol or diesel.

Finally, the friction pump body is made of plastic, which also reduces the weight, with a steel cylinder and a plastic piston. The material for the piston and the rubber sealing rings have been developed specifically to operate with long strokes, while the seal created by the contact between rubber and steel is a great improvement on conventional friction pumps which have a cast iron sealing surface.

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Related entries:

Fiat Bravo Revealed
Fiat Bravo Now With A 1.6 Turbo Diesel Option
Fiat Presents "New" Stilo in Brazil


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