In Detail Suspension and Safety Systems

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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.

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 (the Bravo is now available with 225/45 tyres on 17″ wheels, and optional 225/40 tyres on the 18″ wheels).
  • 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’s 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 20 mm shaft on 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 20 mm.
  • 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.

Five-star EuroNCAP rating

To achieve this, the designers considered every single possible type of accident: head-on and lateral collisions, rollovers, rear-end collisions and fire.

Other factors taken into consideration included the different speeds at which accidents occur, obstacles and the protection of occupants with widely differing physical attributes.

In all, over fifteen thousand hours of computations were carried out, along with sixty crash tests, a hundred and fifty simulations with the HyGe sled and a hundred tests on components and subsystems. These figures are proof of the company’s resolve to make the Bravo one of the safest cars on the road.

This remarkable safety performance has been made possible by the many sophisticated systems available with the new model (standard equipment levels depend on local markets and versions).

These include an array of passive safety devices, with two front airbags (the driver has a two-stage bag), two front side bags, two window bags and a knee airbag for the driver. On top of these are three point seat belts with pretensioners and load limiters, five head-restraints and the FPS fire prevention system.

Bodyshell elements such as the bonnet, door and dashboard cross member also contribute to protecting the occupants. Lastly, a number of other components also play a part in passive safety, such as the seats and steering column, which have been designed bearing in mind their behaviour in a crash.

Furthermore, the new car’s consistent and predictable handling means that it can absorb a certain degree of driver error and easily cope with critical situations. In addition to a high performance brake system, the Fiat Bravo also features the latest generation electronic braking and traction control systems to ensure safe dynamic performance.

These include ABS with EBD (Electronic Brake Force Distribution) and, most importantly, ESP (Electronic Stability Control or stability control), a system that steps in under near critical conditions, when the stability of the car is at risk, to help the driver maintain control of the vehicle.

The ESP system installed on the Fiat Bravo includes a number of additional functions, namely ASR (Anti Slip Regulation or traction control), which limits wheelspin in the event of low grip road conditions; MSR (Engine Torque Regulation), which comes into play during rapid downshifts, reducing engine torque and preventing the drive wheels from locking up; HBA (Hydraulic Brake Assistance), an electronic-hydraulic system that acts in the event of emergency braking; and lastly, the Hill-hold function to facilitate uphill starts.

Braking system and large tyres

In line with its high active safety targets, the Fiat Bravo is equipped with extremely efficient, highly adaptable braking systems. To start with, the braking system is hydraulic, with servo assist, and features 2 cross-over independent circuits (each circuit acts on one front wheel and the opposite rear wheel) to guarantee braking and stability even if one circuit should fail.

All the versions in the range are fitted with ventilated disc brakes at the front, and with solid discs on the rear wheels, which vary with the engine, to reflect the different weight and power. Ventilated discs with a diameter of 257 x 22 mm, and rear discs with a diameter of 251 x 10 mm are fitted.

To achieve the best compromise between handling and comfort, the Fiat Bravo fits large tyres that optimise the car’s performance, particularly in terms of roadholding, safety and comfort on the road. The tyres chosen are: 225/45 R17 and 225/40 R18 (optional).

ABS complete with EBD (Electronic Brake force Distribution)

In addition to its excellent braking system, the Bravo is also equipped with one of the most advanced ABS anti-lock braking systems on the market. It includes a hydraulic control unit with 8 solenoids, 4 active sensors and 4 channels with EBD electronic brake force distribution. The latter distributes the braking force over the four wheels to prevent them from locking, guaranteeing complete control of the car in all conditions. The system also adapts automatically to the grip conditions of the wheels and the efficiency of the brake pads, preventing the latter from overheating.

ESP

The sophisticated ESP system cuts in when conditions are close to the limit, when the car’s stability is at risk, to help the driver to control the vehicle.

To do so, ESP constantly verifies how the tyres grip the ground, longitudinally and laterally, and if the car does skid, it cuts in to recover the trajectory and the stability of the set-up. It incorporates sensors that measure the vehicle’s rotation around its vertical axis (yaw speed), the lateral acceleration and the steering angle set by the driver (which indicates his chosen direction).

It then compares these data with the parameters processed by a computer and uses a complex mathematical model to establish whether the car is taking a bend within grip limits, or whether the front or rear are about to veer (understeer or oversteer).

To bring it back to the correct trajectory, the system generates a yaw moment opposite to the one that caused the instability, singly braking the appropriate wheel (nearside or offside), and reducing engine power by adjusting the throttle valve.

This is where the system developed for the Fiat Bravo differs from other systems. Its intervention on the brakes is modulated to be as gentle as possible (therefore without disturbing driving), and the reduction in engine power is limited, to guarantee excellent performance and enjoyable driving at all times. ESP is always engaged.

HBA (incorporating Hill Holder)

The Hill Holder, which is an integral part of the ESP system, helps the driver during hill starts. It cuts in when the ESP control unit perceives a difference in the inclination of the car through a longitudinal acceleration sensor.

During a hill start, the control unit prepares to cut in when first speed is engaged and the brake and clutch pedals are depressed. The pressure on the front brake callipers is maintained for about 1.5 seconds after the driver removes his foot from the brake pedal, allowing him to set off without difficulty.

The Hill Holder is not activated when the car is started downhill in first gear. The same occurs when reverse is engaged: the system is activated for downhill starts, and it is not activated for uphill starts. And finally, there is the option of HBA, electro-hydraulic brake assistance, which automatically increases the pressure on the braking circuit during panic braking.

ASR (Anti Slip Regulation or traction control)

Another integral element of the ESP system is the ASR (Anti Slip Regulation) system, which optimises traction at all speeds, using the brakes and engine management.

Based on the number of wheel revs calculated by the ABS sensors, the device calculates the degree of slipping and activates two different control systems to recover grip.

When an excessive demand for power causes both drive wheels to slip (for example when aquaplaning or accelerating on an uneven, snow-covered or icy road surface), the system reduces engine torque by decreasing the throttle valve aperture and thus the air flow.

If only one wheel slips (for example the wheel inside a bend following acceleration or dynamic changes to the load), this is automatically braked without the driver having to press the brake pedal. This obtains an effect similar to that of a self-locking differential, enabling the Bravo to tackle road surfaces with poor grip without difficulty.

ASR is engaged automatically every time the engine is started, but can be excluded by a switch on the centre console. It is only necessary to de-activate ASR when fitting snow chains, because in order to transmit torque to the ground, the wheel has to be able to ‘pile up’ snow with small slips that the ASR system tends to avoid.

MSR (Motor Schleppmoment Regelung or engine torque regulation)

This device, also an integral part of the ASR system, cuts in when there is a sudden change of gear when changing down, to return torque to the engine and prevent excessive dragging of the drive wheels, which could cause the car to lose stability when grip is poor.