3363709 - INTRODUCTION - BRAKING SYSTEM
SPECIFCATIONS
In line with standards of excellence, the Stilo is fitted with braking systems:
- of high efficiency
- of excellent modulation
- of safety under all conditions.
The vehicle is also equipped with the most sophisticated electronic and mechanical assistance systems:
- ABS: anti-lock brakes,
- EBD: electronic brake force distribution between front and rear wheels,
- ASR: traction control with intervention at the brakes and the engine,
- MSR: reduction of engine braking torque when changing down a gear,
- ESP: vehicle dynamic stability control,
- EVA (with ASR): panic braking assistance,
- HBA (with ESP): automatic increase in braking pressure during panic braking.
The entire range is fitted with:
- disc brakes on all four wheels,
- ventilated front disc brakes (on all engine types),
- large diameter rear disc brakes (251x10 mm) with Bosch aluminium calipers with automatic clearance recovery (38 mm diameter piston).
- ABS with EBD and ASR,
- panic braking assistance (Brake Assist),
1.2 and 1.6 Versions:
- 257 x 22 mm ventilated disc
- ZOH Bosch brake calipers with 54 mm diameter piston,
- brake pad surface 43 cm[sup2 ]
1.8 and JTD Versions:
- 284 x 22 mm ventilated disc,
- ZOH Bosch brake calipers with 54 mm diameter piston,
- brake pad surface 52 cm[sup2 ]
2.4 Versions:
- 281 x 26 mm ventilated disc,
- ZOH Bosch brake calipers with 57 mm diameter piston,
- brake pad surface 57 cm[sup2 ]
PEDAL UNIT
The pedal unit fitted on this vehicle consists of a mounting with an accelerator pedal made from a special plastic material with the brake and clutch pedals made of steel.The pedal unit has a pedal/brake ratio linked to the diameter of the brake pump, different according to the engine types:
- 1.2, 1.6 and JTD Versions: the ratio is equal to 3.2 linked to the 7/8'' pump,
- 1.8 and 2.4 Versions: the ratio is equal to 3.4 linked to the 15/16'' pump,
BRAKE SERVO
A large diameter (10'') Bosch brake servo is fitted on the Stilo with an aluminium pump and increased travel to guarantee a good pedal travel reserve even in extreme overheating conditions due to intensive usage.
ABS
CONSTRUCTION FEATURES
The Stilo is fitted with an ABS/EBD brake control system.The ABS/EBD system is the Bosch 5.7 type, developed from the 5.3 ABS system and is equipped with 4 active sensors with 4 channels.The ABS is fitted in parallel to the hydraulic brake system so that braking is still assured even if the ABS is faulty.Because the ABS incorporates EBD (Electronic Brakeforce Distribution), a rear load proportioning valve is not fitted.GENERAL VIEW
A.S.R. control/regulation devices
GENERAL VIEW
Specifications
This system carries out all the normal anti-lock and brake distribution functions of the ABS 5.7 with EBD and also ensures the following:
- Acceleration Slip Regulation (A.S.R.)
- engine braking torque regulation (M.S.R.)
- differential lock via action on the brakes (T.C.)
 | The ASR system is disabled if the ABS system is faulty. |
Composition
The system consists of:
- an electronic control unit built into the hydraulic control unit
- a hydraulic control unit which modulates the braking pressure acting on the brakes by means of twelve solenoids regardless of the driver''s actions
- four ACTIVE sensors
- special wiring.
OPERATION
Principles of operation
The system processes the signals coming from the active sensors, the brake light switch and the button for switching the A.S.R. function on/off.It continually compares the speed of wheels on the same side of the car (Front right with Rear right - Front left with Rear left) and causes the ASR to cut in when a speed difference in excess of 2-6 km/h (cut-in threshold) is detected between wheels on the same side. The control unit turns on the MSR function when it detects an excessive difference between the front and rear axles because the front wheels tend to slow down too much compared to the rear wheels.The ABS/ASR control unit communicates continuously with the engine control unit via the C-CAN line.The ASR function is active under all car speed conditions. Braking action is cut out after 80 km/h.
Operating strategies
Drive wheel slippageIntervention - intervention times in road conditions with good grip (asphalt)Torque reduction by the engine control unit by altering ignition advance - 6/100 s after the skid threshold is exceeded;Further torque reduction by reducing throttle opening (by the engine control unit with motorized throttle body) - after 15/100 s.Hydraulic system intervention (braking force on drive wheel) - after 2/10 s.Operation in poor grip conditionsThe system is able to detect this situation by comparing drive wheel acceleration with torque transmitted by the engine (engine load via engine control unit).The system performs in the same way as when both drive wheels are in road conditions with good grip (asphalt) and the cut in thresholds are at the lower limit.Only one drive wheel slippingintervention-intervention timeTorque reduction by the engine control unit by altering ignition advances - 6/100 s after the threshold is exceeded.Further torque reduction by reducing throttle opening (by the engine control unit with motorized throttle body) - after 15/100 s.Effect on hydraulic system, braking action is exerted on the slipping wheel to give the differential a resistive force on the side with poor grip (T.C.).This resistive force allows the differential to transmit an equal torque with good grip.One wheel slipping on a bend with good grip (asphalt).The system detects the presence of a bend from the rear wheel speed (drawn).It implements the same intervention procedures described for when only one drive wheel is slipping; the cut-in thresholds are increased to the upper limit. The torque reduction is applied gradually.One wheel slipping on a bend with poor grip (snow or ice).It implements the same intervention procedures described for when only one drive wheel is slipping; the cut-in thresholds are increased to the lower limit. The torque reduction is accentuated (to ensure good car lateral containment). | Under A.S.R. operating conditions, when the control unit simultaneously receives a signal from the brake light switch, the system ceases to act on the brakes. The torque reduction part remains active. |
| With the brake lights switch activated, but with maximum braking pressure (e.g. tip of heel, defective switch, etc.), if the system detects a speed difference between the front and rear wheels which implies the operation of the A.S.R., only torque reduction is implemented. Brake intervention is excluded. |
Modulating braking torque with engine decelerating
Car instability during deceleration with poor gripThe system recognises the condition from engine load, front and rear wheel speed and brake pedal sensor. In this case, drive torque is increased when the engine control unit cuts in to open the motorised throttle. This overcomes the natural instability of the car due to the engine braking torque with poor grip.Cutting out the asr/mrs system
The ABS and EBD functions remain active if the system is cut out using a button on the panel, as it advisable if the cars are on certain surfaces (deep snow, deep mud, deep sand or gravel), or with chains on the drive wheels.ASR de-activation/activation button
Deactivates the ASR/MSR system and comes with indicator LEDs.The button is built into the central panel
Asr/msr system failure
If the ABS system is faulty, the ASR system is also disabled. The ASR system is cut out with the following faults:
- engine C-CAN message errors
- C-CAN bus error
The ASR warning light strategy is as follows:
- with the A.S.R. on, the warning light in the dashboard is off and the LED on the button is off;
- with the ASR operating, the warning light on the dashboard is intermittent and the LED on the button is off
- with the ASR off, the warning light on the control panel is on, the warning light on the button is on and a message is displayed on the DOT matrix to indicate that the ASR is not activated
- when the ASR is faulty, the panel and button warning lights are on and an anomaly message is displayed on the DOT matrix.
Hydraulic system operation
The hydraulic unit on the version with A.S.R. has 4 additional solenoid valves.The inlet solenoid valve (normally closed), when activated, can receive the additional quantity of fluid required to increase the pressure and brake the wheel/s.The operating solenoid valve (normally open), when activated, allows the modulated pressure produced by the actual pump, necessary for the operation of the ASR, to be maintained in the pump-brake caliper circuit.When the ASR TC function is not on, the ECU:
- does not supply the (N.C.) inlet solenoid valve (2);
- does not supply the (N.A.) operating solenoid valve (3).
When the ASR/TC function is switched on, the electronic control unit:
- supplies the hydraulic pump (1)
- supplies the (N.C.) inlet solenoid valve (2)
- supplies the (N.A.) operating solenoid valve (3).
Hydraulic control unit
The electro-hydraulic control unit consists of:
- twelve two-way solenoid valves;
- a dual circuit electric recovery pump
- two low pressure accumulators
- two high pressure accumulators.
ESP vehicle stability control system
GENERAL VIEW
SPECIFCATIONS
Driving a car under all conditions that may lead to the physical limit of grip and thus of stability may be a difficult task for a normal driver even if the car is stable. To improve driving safety, it is therefore possible to fit an electronic system able to help the driver in this difficult task.Systems currently used to make driving safer under certain conditions are mainly ABS for braking control and TC and ASR/MSR systems. These systems control traction during acceleration by acting on the brakes (T.C.) and traction/drive torque during acceleration and over-run by acting on the brakes and engine control system motorised throttle body (ASR/MSR).The VDC system (Vehicle Dynamic Control) incorporates all the functions listed above and optimises vehicle control with the addition of specific sensors:
- steering angle sensor on the steering wheel
- yaw/side acceleration sensor located near the centre of gravity beneath the central tunnel
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