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Thursday, January 24, 2008

Fiat Bravo: In Depth

Active safety

The Fiat Bravo adopts the most sophisticated electronic systems to control the vehicle dynamic behaviour, which are implemented to raise the dynamic limits even higher, so that they enhance safety but are not intrusive for the driver. The intervention of these devices is the result of simulation and specific tests on the test track, to ensure that they do not detract from the pleasure of driving. A description of the lavish equipment follows.

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. For example, for the 1.4 16 valve engine, ventilated discs with a diameter of 257 x 22 mm are fitted, and rear discs with a diameter of 251 x 10 mm. The version powered by the 120 bhp 1.9 Multijet adopts 284 x 22 mm ventilated discs and solid discs of 251 x 10 mm. And finally, the 150 bhp 1.9 Multijet engine fits 281 x 26 mm ventilated discs and solid discs of 251 x 10 mm.

To achieve the best compromise between handling and comfort, the Fiat Bravo fits large tyres that optimise the car performance, particularly in terms of roadholding, safety and comfort on the road. The tyres chosen (depending on the outfit) are: 205/55 R16, 225/45 R17 and 225/40 R18.

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 (Electronic Stability Program)

The sophisticated ESP system cuts in when conditions are close to the limit, when the car 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 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.

Hill Holder - HBA

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)

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)

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.

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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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