Car Design News: Fiat Bravo: In Depth

Reliable, sophisticated gearboxes

An innovative model like the Fiat Bravo had to be on the cutting edge where gearboxes are concerned, because this component has a decisive influence on driving enjoyment and comfort. The new car offers a choice of two, with two specific variants depending on the engine.

These are the available combinations:

with 6 speeds on the 90 bhp petrol-driven 1.4 16v (C514);
with 5 speeds on the 1.9 Multijet 8v (C530);
with 6 speeds on the 1.9 Multijet 16v (C530).

All the gearboxes share the same dual hose external drive, which guarantees precise manoeuvring, quiet operation and does not transmits mechanical vibration through the control. This is a new generation external control, technologically advanced thanks to the extensive adoption of high performance technopolymers, which are used on the basis of different characteristics of resistance, weight and self-lubricating power.

Bench testing in extreme climate conditions guided the fine-tuning of the materials, couplings and processes, and guarantees the 'robustness' and reliability of the product.

In addition to which, the new drive was designed to guarantee system characteristics, excellent comfort and manoeuvring. A new distribution of the inertia masses was adopted, significantly closer to the gearbox, to raise the level of comfort by increased mechanical filtering.

And huge attention is paid during the assembly of these components to guarantee their quality and reliability, with pre-testing of every component and electronic measurement of all the values that define efficiency, elasticity and 'tolerance'.

The 6 speed gearbox for the 90 bhp 1.4 16v

Enhanced acoustic comfort, reduced engagement effort even when cold and more precise gear engagement. These are the advantages that the motorist can expect from the C514 gearbox (transverse configuration with two cascade shafts and differential) on which various improvements were made to the gear train, synchronisers, lubrication, internal gear control and clutch control, before being used on the Fiat Bravo.

The gearbox is available with six speeds for the 90 bhp 1.4 petrol engine, and adopts a gear control which prevents the involuntary engagement of reverse, thanks to a stroke limiter in the selector, and guarantees more precise engagement of fifth and sixth. With this configuration, the gearbox can transmit up to 128 Nm (13 kgm) at 4500 rpm. The technical characteristics worth highlighting include the gearing housing and clutch housing, both of which have been optimised to reduce weight and to absorb more noise, using FEM (Finite Element Method) calculation techniques. But also Borg-Warner free-ring synchronisation on all speeds. And finally, for first and second, the speeds most used by any motorist, dual cone synchronisers have been fitted, requiring 40% less engagement effort than the conventional single-cone type.

The internal gear control system offers four levels of selection, with a central positioner fitted with bearings. Lubrication is dynamic, and the oil flows are channelled through bore holes in the boxes. The advantages include reduced wear, more efficient torque transmission and better manoeuvring at low temperatures.

The 5-speed gearbox for the 120 bhp 1.9 Multijet (6 speeds for the 150 bhp)

This gearbox is available for the two 1.9 Multijet engines (with 5 speeds for the 120 bhp version and 6 speeds for the 150 bhp version). It stands out for its configuration ? two shafts in a cascade with a differential', and for its excellent manoeuvring and quiet operation. Synchronisation of all forward speeds is of the Borg-Warner free-ring type, and even reverse is synchronised. What is more, on first and second, the synchroniser is of the triple cone type, while the synchroniser on third, fourth, fifth and sixth is of the single-tone type.

The gearshift incorporates a syringe device on the lever knob that prevents involuntary engagement of reverse, and the gear control is activated by a double Bowden metal cable system with an anti-noise device.

Peak torque of 255 Nm (26 kgm) is already available at 2000 rpm on the 120 bhp 1.9 Multijet version, and 305 Nm (31 kgm) on the 150 bhp 1.9 Multijet engine.

And finally, clutch control is hydraulic, incorporated into the gearbox with a CSC device so that it requires less effort to activate, while lubrication is dynamic, guaranteeing less wear, and highly efficient torque transmission and manoeuvrability even at low temperatures.

Suspension that guarantees excellent handling and comfort

One of the goals set by the designers who developed the Bravo was to create a suspension system that would offer performance comparable with that of a higher class of car. Devices that guaranteed easy, pinpoint steering, excellent roadholding and the best comfort possible for passengers. The choice went to two systems that emerged from a project by Magneti Marelli and had already been used on other Fiat models, suitably modified and updated.

Compared to the system adopted on the previous segment C Fiat model, a total review of the geometries brought the following changes:

Tracks widened by 20 mm and larger tyres (in addition to the consolidated 205/55R16, the Bravo is now available with 225/45 tyres on 17 wheels, and 225/40 tyres on 18wheels).
Modified suspension geometry, adoption of a new front anti-roll bar and a new tuning of the springs and shock absorbers suitable for the new bodyshell, with the best torsional rigidity in the segment, new oversized right-angled lower links designed to separate the effect of the braking loads from the cornering loads to guarantee the best balance in all driving conditions. In addition to which, in spite of the wider track, the front geometry design combined with the stroke of the steering boxes also made it possible to contain the car turning circle: 10.5 m between kerbs and 11 m between walls (values that are the best in the segment).
Rear suspension with interconnected semi-independent wheels and a torsion axle created with a new stiffer anti-roll bar to increase structural rigidity and to maintain good suspension flexibility under load, thanks to a reinforced hydraulic bushing to connect the rear axle to the bodyshell. The suspension design also resulted in new springs, dampers and buffers, in order to adapt to the bodyshell and to improve the dynamic response on corners.
Particular attention went into the design of the components that could affect comfort in the car, adopting solutions typical of higher segment cars, such as a 'dual-path' strut mount at the front and a vertical shock absorber at the rear. These measures made it possible to limit the effect of the vibration generated by the road surface, without altering the structural rigidity or detracting from steering precision.
To increase stability on corners, the new car adopts dampers with a 22 mm shaft on the Multijet versions (20 mm on the 1.4 petrol engined versions) and a stiffened reinforced hollow bar that also reduces the weight.
Increase in the structural rigidity of the front suspension anchorage crossbeam to improve acoustic and vibrational comfort and to improve handling.
And finally, the track of the front and rear suspension was widened, both to adapt it to the larger exterior measurements of the new model and to improve driving stability.

Front

The Fiat Bravo adopts an independent layout in which the shock absorbers and springs act as both damping and elastic elements and as structural and kinematic elements. The main components of this layout are the twin-shell wishbones made of pressed sheet metal and not cast iron, which means a significant weight reduction. The new model also introduces some extremely interesting solutions:

Front suspension crossbeam with great structural rigidity, with a transverse connecting 'strap' close to the front strut attachments.
'Dual-path' strut blocks to improve filtering of road vibration, while guaranteeing excellent structural rigidity, and enhancing steering precision.
Stiffened anti-roll bar to limit vehicle rolling, with shock absorber anchorage rods which boost the stabilising efficiency and improve the promptness of the dynamic response when cornering.
New stiffer coil springs made with the 'side-load' technique that optimise the thrust axis so as to reduce the tangential forces on the damper shaft and therefore the internal friction (system hysteresis), which improves absorption of minor road roughness.
To raise lateral rigidity and improve handling on corners, the new model fits dual-rate telescopic dampers with a shaft diameter of 22 mm on the Multijet versions and of 20 mm on versions with the 1.4 petrol engine.
And finally, bodyshell stiffening has been increased and the upper anchorage to the bodyshell has been redesigned, increasing the rigidity and the caster angle, which in turn enhances steering precision and comfort.

Rear

The Fiat Bravo fits an optimised semi-independent system with interconnected wheels and a torsion axle. The new hollow anti-roll bar has been made 40% stiffer in order to achieve a 40% anti-roll stabilising effect, improving steering precision and roadholding. The soundproofing of the vertical dampers, which are attached to the bodyshell in the wheelarches, has been improved, to filter road roughness better, enhancing acoustic comfort in the passenger compartment.

And finally, the structure of the rear axle comprises lateral arms pressed in two semi-shells, which are welded to a lateral torsion profile, and the new anti-roll bar that passes inside the crossbeam and is welded to the struts. The rear axle attachment bushings are hydraulic to guarantee better longitudinal absorption and comfort than the rubber-metal type, with improved shoulders and reinforcement.