Introduction - BRAKING SYSTEM

07/03 to 12/03, from 01/04

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 system is the hydraulic power assisted type: it consists of two independent crossover circuits (each circuit acts on a front wheel and the diagonally opposed rear wheel) to ensure braking and stability even if one circuit should fail.

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),

Given the difference in weight and power of the different engine types, the front braking system differs as follows:

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 ]

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,

The accelerator control is electronic for all versions.

A - Pedal unit for Selespeed gearbox

B - Pedal unit for manual gearbox

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.

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

1 - ABS/EBD control unit

2 - Front wheel sensor left

3 - Front wheel sensor right

4 - Rear right wheel right

5 - Rear wheel sensor left

6 - EBD warning light

7 - ABS warning light

CONSTRUCTION FEATURES

In addition to the ABS EBD system, some Stilo vehicles may be fitted with a drive control system (ASR/MSR) or a vehicle stability control system (ESP).

These two systems are a further development of the ABS 5.7 system featuring improved specifications.

By means of its yaw and steering wheel angular position sensors, the ESP system is able to monitor whole car dynamics and increase active safety.

GENERAL VIEW

1 - ABS/ASR control unit

2 - Engine management control unit

3 - Front left sensor

4 - Front right sensor

5 - ASR off button

6 - Rear right sensor

7 - Rear left sensor

8 - ASR warning light

9 - EBD warning light

10 - ABS warning light

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 functions are ensured by adjusting drive torque and applying a braking force to one or both drive wheels.

The A.S.R. control unit calculates the slip of the drive wheels from the difference between the number of revs for the front and rear wheels detected by the ABS sensors.

If one or both drive wheels tend to slip during acceleration, the control unit orders the engine control unit to reduce the torque transmitted by the engine to the wheels (through a decrease in the air flow rate implemented by closing the motorized throttle) and almost simultaneously brakes the wheel or wheels without the driver having to do anything.

If the wheels tend to lock during hard deceleration, the ABS control unit requests the engine control unit to adjust engine braking toruqe to prevent car stability.

The system can be cut out by activating a button located on the console.

ASR/MSR intervention is indicated by the warning light on the dashboard flashing.

Each time the vehicle is started up the ASR/MSR function is activated, even if the ignition has been turned off with the function deactivated.

The system can be excluded by pressing the button on the tunnel. Exclusion is signalled by the warning light on the actual button coming on.

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.

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.

1 - A.B.S./A.S.R. control unit

2 - Engine management control unit

3 - Wheel rpm sensors (active)

4 - Brake pedal switch

5 - A.S.R. on/off button

6 - A.S.R. on/off LED

7 - Motorised throttle body

8 - Ignition system (advance adjustment)

8 - Ignition system (advance adjustment)

10 - Brake calipers

11 - Body Computer

Drive wheel slippage

Intervention - 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 conditions

The 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 slipping

intervention-intervention time

Torque 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.

Car instability during deceleration with poor grip

The 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

1 - Led

2 - ASR deactivation button

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 control unit activates warning lights on the control panel and button when these anomalies occur.

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.

The warning lights are governed by the ABS control unit by means of a C-CAN network as with the ABS with EBD.

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).

In this way the system operates like the Bosch 5.7 ABS.

1 - Pump

2 - Inlet solenoid valve

3 - Pilot solenoid

4 - Brake calipers

5 - De-pressurizing solenoid valve

6 - Pressuring solenoid valve

Hydraulic system operation

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).

Then pressure generated by pump (1) then reaches the brake calipers and is modulated, upon a command by the electronic control unit, by the de-pressurizing (5) and pressurizing (6) solenoid valves.

1 - Pump

2 - Inlet solenoid valve

3 - Pilot solenoid

4 - Brake calipers

5 - De-pressurizing solenoid valve

6 - Pressuring solenoid valve

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.

1 - Brake servo pump

2 - Hydraulic control unit

3 Rear left wheel

4 - Front right wheel

5 - Front left wheel

6 - Rear right wheel

GENERAL VIEW

1 - ABS/ESP control unit

2 - Steering angle sensor

3 - Engine management control unit

4 - Yaw/lateral acceleration sensor

5 - Front right wheel sensor

6 - ASR off button

7 - Rear right wheel sensor

8- Rear left wheel sensor

9 - ESP warning light

10 - EBD warning light

11 - ABS warning light

12 - Front left wheel sensor

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

μ - wheel grip

S - slip

A - EBD intervention area

B - ABS intervention area

C - ESP intervention area

1 - Side force curve

2 - Longitudinal force curve

SPECIFCATIONS

As may be seen from the grip/slip diagram, the ESP system covers a bigger area than a conventional ABS/EBD.

The VDC cannot be cut out because it is a safety system; the ASR/MSR function can, however, be cut out by means of a button on the central facia

VDC system intervention is indicated by a special warning light on the instrument panel node (Italian acronym = NQS)

Composition

The VDC system consists of:

• a special A.B.S.5.7 hydraulic/electronic control unit (with V.D.C. function)
• interface with the C-CAN line resident in the ABS control unit for communication with the body computer robotised gearbox motor control unit and steering angle sensor
• magnetoresistive wheel speed sensors
• steering angle sensor with CAN interface (steering angle node)
• yaw/side acceleration sensor integrated within a single component
• brake fluid pressure sensor integrated in the ABS control unit
• VDC warning light controlled via CAN line
• ASR deactivation switch with warning light on button

ASR deactivation is indicated at the NQS by means of a message on the DOT matrix.

OPERATION

The VDC system continuously detects loss of longitudinal and transverse wheel grip under all driving conditions, from braking to acceleration, to ensure vehicle directionality and stability.

The VDC system is managed by a Bosch 5.7 ABS ECU integral with a special hydraulic control unit that makes it possible for the brake system to be operated independently of the driver.

The control unit processes the following signals:

• steering angle/steering wheel rotation speed
• side acceleration and yaw
• motorised throttle position
• wheel rpm
• hydraulic braking system pressure

and uses special algorithms in the software to obtain the values for dynamic control of the vehicle:

• longitudinal and transverse slip between wheels and road surface
• axle drift.

The system calculates actual vehicle dynamics from these values; and identifies all critical conditions due to environmental factors (e.g. surface with poor grip) or any mistakes made by the driver (e.g. panic situations) to restore the car to efficient handling conditions by adjusting the brakes and drive torque.

The system interfaces with:

• N.C.M. for drive torque modulation,
• N.C.R. (robotised gearbox node) for gear shift management
• N.B.C. (body computer node) to transmit vehicle speed values and control warning lights.

Information is exchanged between these components by means of the C-CAN and B-CAN lines.

System diagnosis is carried out via a dedicated line (K line).

The system is linked to a power unit with a special brake pump; the pipes between brake pump and ABS control unit are also fitted with a Titaflex insert because the pipe diameter is bigger (6 mm) than normal pipes (4 mm); this is to prevent negative effects on ESP operation at low brake fluid temperatures.

The VDC comes on automatically when the vehicle is started up and cannot be switched off by the driver; the button on the central console turns off only the ASR function and only in recommended circumstances (see ASR system).

OPERATION

INPUT SIGNALS:

• Wheel speed sensors (from direct line) (3)
• Brake pedal switch (4)
• Brake pedal switch wiring diagram (5)
• ASR button off (from direct line) (6)
• Engine control unit (2)
• Throttle angle position (from C-CAN line)
• Body computer (14)
• Handbrake lever position (from C-CAN line)
• Warning light status indicator (from C-CAN line) (11)
• Yaw sensor (rotation around vehicle vertical axis (from direct line) (10)
• Lateral acceleration sensor (from direct line) (10)
• Steering wheel steering angle/rotation sensor ((from C-CAN line) (12)
• Robotised gearbox control unit (speed engaged status) (from C-CAN line) (13)
• Hydraulic system pressure sensor(from direct line) (1)

OUTPUT SIGNALS:

• Brake pressure modulation command (15)
• Ignition advance reduction command (from C-CAN line) (9)
• Engine power management command (from C-CAN line) (8)
• Gear change inhibition (from C-CAN line) (13)
• Wheel speed signal for speedometer and mileometer (from C-CAN line) (14)
• VSO (vehicle speed) signal (14)
• ESP warning light control on panel (from C-CAN line) (11)
• ASR LED off (7)

OPERATING LOGICS

As explained previously, the ESP controls longitudinal vehicle slip and also transverse slip, i.e. vehicle lateral stability.

Vehicle lateral stability is provided by tyre reaction to lateral forces and depends on the strength with which the wheel grips the road surface.

A wheel's adhesive force depends on vertical load, which depends in turn on wheel situation (supporting or unladen) and friction coefficient, which depends in turn on surface and tyre conditions.

When the vehicle is moving in a straight line, the effect of side forces may be disregarded, unless external factors increase their intensity (e.g. wind gusts or changeover to a different surface). Conversely, when the car corners, side forces increase greatly due to the increase in centrifugal force.

The action of side forces brings about a change in wheel drift angle and thus a change in axle drift (drift angle = difference between required trajectory and actual trajectory).

The side forces do not act equally on all four wheels because the wheels are not subject to the same load conditions. Wheels are loaded differently in different situations. The following situations may occur:

• acceleration (lightening of front axle and loading of rear axle)
• braking (loading of front axle and lightening of rear axle)
• right/left bend (loading of outside wheels and lightening of inside wheels)
• cornering while accelerating/decelerating (combination of the above cases)

If the side forces acting on individual wheels vary, it follows that the resultant forces acting on the car axles also vary. This means that if side forces acting on the front axle prevail over the forces acting on the rear axle or viceversa, the vehicle's vertical axis (yaw axis) is subject to a rotary force (moment).

The yawing moment affects car behaviour and generates a state of understeer or oversteer.

A vehicle is said to be understeered when the front axle drift angle increase to a greater extent than that of the rear axle when subject to increasing side acceleration. In this case, the car tends to go straight when turning a corner (it tends to take the curve wide).

OPERATING LOGICS

A car is said to be oversteered when the rear axle drift angle increases to a greater extent than that of the front axis with increasing transverse acceleration. In this case, the vehicle tends to spin around (the rear axle tends to go straight and the vehicle cuts the corner).

OPERATING LOGICS

To keep the influence of side forces under control and thus limit the yawing moment, the ABS 5.7 control unit must firstly compute the vehicle behaviour set by the driver on the basis of:

• steering angle sensor/steering wheel rotation speed
• accelerator pedal position
• braking system pressure

after which the control unit assesses actual vehicle behaviour by means of:

• the sensors on the wheels (car speed/wheel speed)
• side acceleration sensor
• yaw sensor.

The above shows that the control unit is able to:

• perceive the driver's actions because steering wheel position shows the number of degrees by which (large radius or short radius bend) and the speed with which the steering wheel is turned (sudden or gradual turns). Throttle position and brake pressure also show whether the car is accelerating or braking. In other words, how the driver takes the corner or deviates from a straight trajectory.
• perceive actual vehicle behaviour on the basis of environmental variables e.g. slippery surface, car reactions to incorrect manoeuvres by the driver etc. in order to identify yawing moment and axle side slip by means of sensors on all four wheels and the yaw and side acceleration sensor.

These two operations are necessary to compare the mathematical model mapped in the control unit with actual car behaviour in order to identify vehicle status (understeer or oversteer) and decide the action to be taken on the brakes and engine.

Understeering on corners

The control unit monitors to detect understeer (prevalence of front axle drift) and corrects car behaviour by braking the wheels on the inside of the bend to create an opposite moment in order to bring the car toward the middle of the bend and reducing drive torque if necessary.

Oversteering on corners

The car detects the presence of oversteer (prevalence of rear axle drift) and corrects vehicle behaviour by braking the front wheel on the outside of the bend to create an opposite yawing moment, possibly augmented by an increase in the driving torque.

The system intervenes before understeer and oversteer reach excessive levels in order to limit countersteering manoeuvres that could be difficult to handle.

Abrupt changes in straight trajectory (swerving/overtaking)

In the case of abrupt changes in trajectory (e.g. overtaking/swerving, the control unit identifies possible oversteer or understeer conditions and correct vehicle trajectory as described above.

Abrupt change in straight trajectory (driving over different surfaces)

The control unit can preceive deviations from the trajectory and prevalence of axle drift, and corrects the trajectory with appropriate actions on the brakes and engine.

Brusque acceleration/deceleration

The control unit acts on the A.S.R./M.S.R. strategy it controls vehicle side acceleration and thus regulates the action on the front and rear brakes and driving torque more fully than on cars with ASR only.

Cutting out ASR

If the ASR/MSR is cut out the following functions remain active:

• A.B.S./E.B.D.
• T.C. up to a speed of 40 km per hour
• partial V.D.C.

Displaying VDC intervention

When the ESP system intervenes, a warning light on the control panel flashes (5 Hz c.c. 50%).

The VDC increases driving safety but cannot control extreme situations. The system should not be seen as a performance-enhancing device but as a device that increases vehicle safety.

Hydraulic system operation

The hydraulic unit on the version with V.D.C. comes with 4 additional solenoid valves.

When activated, the inlet solenoid valve (normally closed) 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 to be maintained in the circuit.

When the ESP does not intervene, the ECU:

• does not activate the inlet solenoid (N.C.) (2).
• does not activate the operating solenoid (N.0.) (3).

In this way the system operates like the Bosch 5.7 ABS.

Hydraulic system operation

During V.D.C. intervention, the ECU:

• activates the hydraulic aggregate pump (1)
• activates the inlet solenoid (N.C.) (2)
• activates the operating solenoid (N.O.) (3).

Then pressure generated by pump (1) then reaches the brake calipers and is modulated, upon a command by the electronic control unit, by the de-pressurizing (5) and pressurizing (6) solenoid valves.

Specifications

In the case of a brusque upwards gear change on a road with poor grip and the consequent slipping of the drive wheels, the MSR system intervenes automatically increasing the engine torque in order to reduce excessive drag of the drive wheels.

Specifications

It has been shown that in panic situations not all drivers are capable of obtaining the best possible performance from their vehicle's braking system. In effect, many of them limit the system's capabilities even though they apply the brakes quickly; there are two reasons for this:

• the first is linked to the fact that they have braked using the same force as in normal conditions,
• the second is connected to the psychological fear of the brakes locking even though ABS is fitted.

The device is therefore given the taks of recognizing an emergency situation and consequently increasing the pressure on the system until maximum performance compatible with the vehicle grip limits is produced. The same deceleration is produced through a reduction in the force on the pedal of up to a third compared with normal braking.

In addition to the braking distance, the stopping distance consists of the distance covered both in terms of reaction time and braking response time. By reducing the latter, especially at high speeds, the device is capable of reducing the stopping distance.

Components

On the Stilo this function is carried out:

• by a mechanical device housed in the brake servo pump unit (E.V.A. Emergency Valve Assistance) on vehicles fitted with ASR
• by a motor on the hydaulic aggregate electronically operated by the ABS control unit (H.B.A. Hydraulic Brake Assistance) on vehicles with ESP.

The E.V.A. device uses the hydraulic reaction of the brake pump to produce a very high assistance ratio in the case of panic braking (the intervention level is linked to the application speed).

H.B.A. is an ESP software module which controls the pressure increase gradient when the driver brakes. A panic situation is recognized when this gradient exceeds the pre-set level.

On both devices the speed threshold is set so that it only intervenes in genuine panic situations without affecting the pedal in normal vehicle usage conditions.

Section of brake servo with conventional pump

1 - Reaction disc

2 - Valve piston

Components

Section of brake servo with EVA device

1 - Fast ratio piston

2 - Slow ratio piston

3 - Brake pump

4 - EVA device

07/02 to 06/03, 07/03 to 12/03, up to 06/02

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 system is the hydraulic power assisted type: it consists of two independent crossover circuits (each circuit acts on a front wheel and the diagonally opposed rear wheel) to ensure braking and stability even if one circuit should fail.

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),

Given the difference in weight and power of the different engine types, the front braking system differs as follows:

Engine types: 1.2, 1.4 and 1.6:

• 257 x 22 mm ventilated disc
• ZOH Bosch brake calipers with 54 mm diameter piston,
• brake pad surface 43 cm[sup2 ]

Engine types: 1,8, 1.9 JTD (80CV and 115CV):

• 284 x 22 mm ventilated disc,
• ZOH Bosch brake calipers with 54 mm diameter piston,
• brake pad surface 52 cm[sup2 ]

Engine types: 1.9 JTD 16V and 2.4:

• 281 x 26 mm ventilated disc,
• ZOH Bosch brake calipers with 57 mm diameter piston,
• brake pad surface 57 cm[sup2 ]

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,

The accelerator control is electronic for all versions.

A - Pedal unit for Selespeed gearbox

B - Pedal unit for manual gearbox

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.

CONSTRUCTION FEATURES

The Stilo is fitted with an ABS/EBD brake control system.

The ABS/EBD system is the Bosch 8.0, developed from the system formerly fitted to other cars and it is equipped with 4 active sensors and 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

1 - ABS/EBD control unit

2 - Front left wheel sensor

3 - Front right wheel sensor

4 - Rear right wheel sensor

5 - Rear left wheel sensor

6 - EBD warning light

7 - ABS warning light

CONSTRUCTION FEATURES

In addition to the ABS EBD system, some Stilo vehicles may be fitted with a drive control system (ASR/MSR) or a vehicle stability control system (ESP).

These two systems are a further development of the ABS 8.0 system featuring improved specifications.

By means of its yaw and steering wheel angular position sensors, the EPS system is able to monitor whole car dynamics and increase active safety.

PINOUT

The control unit pin out is illustrated in the diagram below.

1. Earth

2. +30 supply

3. +30 supply

4. Earth

5. Connection with left front wheel sensor

6. Connection with left rear wheel sensor

7. N.C.

8. Connection with right rear wheel sensor

9. Connection with right front wheel sensor

10. Connection with right front wheel sensor

11. Diagnostic line K

12. N.C.

13. N.C.

14. N.C.

15. C CAN-L connection

16. Connection with left front wheel sensor

17. Connection with left rear wheel sensor

18. Ignition-operated power supply +15

19. Connection with right rear wheel sensor

20. N.A. signal from brake pedal switch

21. N.C.

22. N.C.

23. Connection with body computer node

24. N.C.

25. N.C.

26. C CAN-H connection

From 06/03, the ASR function will be provided only in conjunction with the ESP, described below

GENERAL VIEW

2 - Engine management control unit

2 - Front sensor left

3 - Front sensor right

4 - ASR off button

5 - Rear sensor right

6 - Rear sensor left

7 - ASR warning light

8 - EBD warning light

9 - ABS warning light

SPECIFCATIONS

This system carries out all the normal anti-lock and brake distribution functions of the ABS 8.0 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 functions are ensured by adjusting drive torque and applying a braking force to one or both drive wheels.

The A.S.R. control unit calculates the slip of the drive wheels from the difference between the number of revs for the front and rear wheels detected by the ABS sensors.

If one or both drive wheels tend to slip during acceleration, the control unit orders the engine control unit to reduce the torque transmitted by the engine to the wheels (through a decrease in the air flow rate implemented by closing the motorized throttle) and almost simultaneously brakes the wheel or wheels without the driver having to do anything.

If the wheels tend to lock during hard deceleration, the ABS control unit requests the engine control unit to adjust engine braking toruqe to prevent car stability.

The system can be cut out by activating a button located on the console.

ASR/MSR intervention is indicated by the warning light on the dashboard flashing.

Each time the vehicle is started up the ASR/MSR function is activated, even if the ignition has been turned off with the function deactivated.

The system can be excluded by pressing the button on the tunnel. Exclusion is signalled by the warning light on the actual button coming on.

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.

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.

1 - A.B.S./A.S.R. control unit

2 - Engine management control unit

3 - Wheel rpm sensors (active)

4 - Brake pedal switch

5 - A.S.R. on/off button

6 - A.S.R. on/off LED

7 - Motorised throttle body

8 - Ignition system (advance adjustment)

8 - Ignition system (advance adjustment)

10 - Brake calipers

11 - Body Computer

Drive wheel slippage

Intervention - 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 under conditions of poor grip

The 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 slipping

intervention-intervention time

Torque 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.

Car instability during deceleration with poor grip

The 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

1 - Led

2 - ASR deactivation button

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 control unit activates warning lights on the control panel and button when these anomalies occur.

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.

The warning lights are governed by the ABS control unit by means of a C-CAN network as with the ABS with EBD.

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).

In this way the system operates like the Bosch 8.0 ABS.

1 - Pump

2 - Inlet solenoid valve

3 - Pilot solenoid

4 - Brake calipers

5 - De-pressurizing solenoid valve

6 - Pressuring solenoid valve

Hydraulic system operation

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).

Then pressure generated by pump (1) then reaches the brake calipers and is modulated, upon a command by the electronic control unit, by the de-pressurizing (5) and pressurizing (6) solenoid valves.

1 - Pump

2 - Inlet solenoid valve

3 - Pilot solenoid

4 - Brake calipers

5 - De-pressurizing solenoid valve

6 - Pressuring solenoid valve

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.

1 - Brake servo pump

2 - Hydraulic control unit

3 Rear left wheel

4 - Front right wheel

5 - Front left wheel

6 - Rear right wheel

GENERAL VIEW

1 - ABS/ESP control unit

2 - Steering angle sensor (integrated in the electric steering motor)

3 - Yaw/lateral acceleration sensor

4 - Front wheel sensor right

5 - ASR off button

6 - Rear wheel sensor right

7 - Rear wheel sensor left

8 - ESP warning light

9 - EBD warning light

10 - ABS warning light

11 - Front wheel sensor left

PINOUT

The control unit pin out is illustrated in the diagram below.

1. Earth

2. +30 supply

3. +30 supply

4. Earth

5. Connection with left front wheel sensor

6. Connection with left rear wheel sensor

7. N.C.

8. Connection with right rear wheel sensor

9. Connection with right front wheel sensor

10. Connection with right front wheel sensor

11. Diagnostic line K

12. N.C.

13. N.C.

14. C CAN-L connection

15. Earth for yaw sensor

16. Signal input from yaw sensor

17. N.C.

18. Reference signal for yaw sensor

19. N.C.

20. Lateral acceleration signal input in 'g'.

21. N.C.

22. N.C.

23. N.C.

24. N.C.

25. N.C.

26. Connection with left front wheel sensor

27. Connection with left rear wheel sensor

28. Ignition-operated power supply +15

29. Connection with right rear wheel sensor

30. N.A. signal from brake pedal switch

31. ASR system deactivation

32. N.C.

33. Connection with the body computer node

34. N.C.

35. C CAN-H connection

36. N.C.

37. Test signal for yaw sensor

38. N.C.

39. N.C.

40. N.C.

41. N.C. signal from brake pedal switch

42. N.C.

43. N.C.

44. N.C.

45. N.C.

46. ASR system warning light control

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 ESP system incorporates all the functions listed above and optimises vehicle control with the addition of specific sensors:

• steering angle sensor incorporated in the electric steering motor
• yaw/lateral acceleration sensor located near the centre of gravity beneath the central tunnel

m - Wheel grip

S - Slip

A - EBD intervention area

B - ABS intervention area

C - ESP intervention area

1 - Side force curve

2 - Longitudinal force curve

SPECIFCATIONS

As may be seen from the grip/slip diagram, the ESP system covers a bigger area than a conventional ABS/EBD.

The ESP cannot be cut out because it is a safety system; the ASR/MSR function can, however, be cut out by means of a button on the central facia

ESP system intervention is indicated by a special warning light on the instrument panel node (Italian acronym = NQS)

COMPOSITION

The ESP system consists of:

• a special A.B.S.8.0 hydraulic/electronic control unit (with ESP function)
• interface with the C-CAN line resident in the ABS control unit for communication with the engine management control unit, robotised gearbox, boyd computer and electric steering control unit
• magnetoresistive wheel speed sensors
• yaw/side acceleration sensor integrated within a single component
• brake fluid pressure sensor integrated in the ABS control unit
• ESP warning light controlled via CAN line
• ASR deactivation switch with warning light on button

ASR deactivation is indicated at the NQS by means of a message on the DOT matrix.

OPERATION

The ESP system continuously detects loss of longitudinal and transverse wheel grip under all driving conditions, from braking to acceleration, to ensure vehicle directionality and stability.

The ESP system is managed by a Bosch 8.0 ABS ECU integral with a special hydraulic control unit that makes it possible for the brake system to be operated independently of the driver.

The control unit processes the following signals:

• steering angle/steering wheel rotation speed
• side acceleration and yaw
• motorised throttle position
• wheel rpm
• hydraulic braking system pressure

and uses special algorithms in the software to obtain the values for dynamic control of the vehicle:

• longitudinal and transverse slip between wheels and road surface
• axle drift.

The system calculates actual vehicle dynamics from these values; and identifies all critical conditions due to environmental factors (e.g. surface with poor grip) or any mistakes made by the driver (e.g. panic situations) to restore the car to efficient handling conditions by adjusting the brakes and drive torque.

The system interfaces with:

• N.G.E. for the acquisition of the steering angle value
• N.C.M. for drive torque modulation,
• N.C.R. (robotised gearbox node) for gear shift management
• N.B.C. (body computer node) to transmit vehicle speed values and control warning lights.

Information is exchanged between these components by means of the C-CAN and B-CAN lines.

System diagnosis is carried out via a dedicated line (K line).

The system is linked to a power unit with a special brake pump; the pipes between brake pump and ABS control unit are also fitted with a Titaflex insert because the pipe diameter is bigger (6 mm) than normal pipes (4 mm); this is to prevent negative effects on ESP operation at low brake fluid temperatures.

The EPS comes on automatically when the vehicle is started up and cannot be switched off by the driver. the button on the central console turns off only the ASR function and only in recommended circumstances (see ASR system).

OPERATION

INPUT SIGNALS:

• Wheel speed sensors (from direct line) (3)
• Brake pedal switch (4)
• Brake pedal switch wiring diagram (5)
• ASR button off (from direct line) (6)
• Engine control unit (2)
• Throttle angle position (from C-CAN line)
• Body computer (14)
• Handbrake lever position (from C-CAN line)
• Warning light status indicator (from C-CAN line) (11)
• Yaw sensor (rotation around vehicle vertical axis (from direct line) (10)
• Lateral acceleration sensor (from direct line) (10)
• Steering angle/steering wheel rotation sensor (from the C-CAN line from the electric steering control unit) (12)
• Robotised gearbox control unit (speed engaged status) (from C-CAN line) (13)
• Hydraulic system pressure sensor(from direct line) (1)

OUTPUT SIGNALS:

• Brake pressure modulation command (15)
• Ignition advance reduction command (from C-CAN line) (9)
• Engine power management command (from C-CAN line) (8)
• Gear change inhibition (from C-CAN line) (13)
• Wheel speed signal for speedometer and mileometer (from C-CAN line) (14)
• VSO (vehicle speed) signal (14)
• ESP warning light control on panel (from C-CAN line) (11)
• ASR LED off (7)

OPERATING LOGICS

As explained previously, the ESP controls longitudinal vehicle slip and also transverse slip, i.e. vehicle lateral stability.

Vehicle lateral stability is provided by tyre reaction to lateral forces and depends on the strength with which the wheel grips the road surface.

A wheel's adhesive force depends on vertical load, which depends in turn on wheel situation (supporting or unladen) and friction coefficient, which depends in turn on surface and tyre conditions.

When the vehicle is moving in a straight line, the effect of side forces may be disregarded, unless external factors increase their intensity (e.g. wind gusts or changeover to a different surface). Conversely, when the car corners, side forces increase greatly due to the increase in centrifugal force.

The action of side forces brings about a change in wheel drift angle and thus a change in axle drift (drift angle = difference between required trajectory and actual trajectory).

The side forces do not act equally on all four wheels because the wheels are not subject to the same load conditions. Wheels are loaded differently in different situations. The following situations may occur:

• acceleration (lightening of front axle and loading of rear axle)
• braking (loading of front axle and lightening of rear axle)
• right/left bend (loading of outside wheels and lightening of inside wheels)
• cornering while accelerating/decelerating (combination of the above cases)

If the side forces acting on individual wheels vary, it follows that the resultant forces acting on the car axles also vary. This means that if side forces acting on the front axle prevail over the forces acting on the rear axle or viceversa, the vehicle's vertical axis (yaw axis) is subject to a rotary force (moment).

The yawing moment affects car behaviour and generates a state of understeer or oversteer.

A vehicle is said to be understeered when the front axle drift angle increase to a greater extent than that of the rear axle when subject to increasing side acceleration. In this case, the car tends to go straight when turning a corner (it tends to take the curve wide).

OPERATING LOGICS

A car is said to be oversteered when the rear axle drift angle increases to a greater extent than that of the front axis with increasing transverse acceleration. In this case, the vehicle tends to spin around (the rear axle tends to go straight and the vehicle cuts the corner).

OPERATING LOGICS

To keep the influence of side forces under control and thus limit the yawing moment, the ABS 8.0 control unit must firstly compute the vehicle behaviour set by the driver on the basis of:

• steering angle value/steering wheel rotation speed
• accelerator pedal position
• braking system pressure

after which the control unit assesses actual vehicle behaviour by means of:

• the sensors on the wheels (car speed/wheel speed)
• side acceleration sensor
• yaw sensor.

The above shows that the control unit is able to:

• perceive the driver's actions because steering wheel position shows the number of degrees by which (large radius or short radius bend) and the speed with which the steering wheel is turned (sudden or gradual turns). Throttle position and brake pressure also show whether the car is accelerating or braking. In other words, how the driver takes the corner or deviates from a straight trajectory.
• perceive actual vehicle behaviour on the basis of environmental variables e.g. slippery surface, car reactions to incorrect manoeuvres by the driver etc. in order to identify yawing moment and axle side slip by means of sensors on all four wheels and the yaw and side acceleration sensor.

These two operations are necessary to compare the mathematical model mapped in the control unit with actual car behaviour in order to identify vehicle status (understeer or oversteer) and decide the action to be taken on the brakes and engine.

Understeering on corners

The control unit monitors to detect understeer (prevalence of front axle drift) and corrects car behaviour by braking the wheels on the inside of the bend to create an opposite moment in order to bring the car toward the middle of the bend and reducing drive torque if necessary.

Oversteering on corners

The car detects the presence of oversteer (prevalence of rear axle drift) and corrects vehicle behaviour by braking the front wheel on the outside of the bend to create an opposite yawing moment, possibly augmented by an increase in the driving torque.

The system intervenes before understeer and oversteer reach excessive levels in order to limit countersteering manoeuvres that could be difficult to handle.

Abrupt changes in straight trajectory (swerving/overtaking)

In the case of abrupt changes in trajectory (e.g. overtaking/swerving, the control unit identifies possible oversteer or understeer conditions and correct vehicle trajectory as described above.

Abrupt change in straight trajectory (driving over different surfaces)

The control unit can preceive deviations from the trajectory and prevalence of axle drift, and corrects the trajectory with appropriate actions on the brakes and engine.

Brusque acceleration/deceleration

The control unit acts on the A.S.R./M.S.R. strategy it controls vehicle side acceleration and thus regulates the action on the front and rear brakes and driving torque more fully than on cars with ASR only.

Cutting out ASR

If the ASR/MSR is cut out the following functions remain active:

• A.B.S./E.B.D.
• T.C. up to a speed of 40 km per hour
• partial ESP.

ESP intervention display

When the ESP system intervenes, a warning light on the control panel flashes (5 Hz c.c. 50%).

The ESP increases driving safety but cannot control extreme situations. The system should not be seen as a performance-enhancing device but as a device that increases vehicle safety.

Hydraulic system operation

The hydraulic unit on the version with ESP comes with 4 additional solenoid valves.

When activated, the inlet solenoid valve (normally closed) 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 to be maintained in the circuit.

When the ESP does not intervene, the ECU:

• does not activate the inlet solenoid (N.C.) (2).
• does not activate the operating solenoid (N.0.) (3).

In this way the system operates like the Bosch 8.0 ABS.

Hydraulic system operation

During ESP intervention, the ECU:

• activates the hydraulic aggregate pump (1)
• activates the inlet solenoid (N.C.) (2)
• activates the operating solenoid (N.O.) (3).

Then pressure generated by pump (1) then reaches the brake calipers and is modulated, upon a command by the electronic control unit, by the de-pressurizing (5) and pressurizing (6) solenoid valves.

Specifications

In the case of a brusque upwards gear change on a road with poor grip and the consequent slipping of the drive wheels, the MSR system intervenes automatically increasing the engine torque in order to reduce excessive drag of the drive wheels.

Specifications

It has been shown that in panic situations not all drivers are capable of obtaining the best possible performance from their vehicle's braking system. In effect, many of them limit the system's capabilities even though they apply the brakes quickly; there are two reasons for this:

• the first is linked to the fact that they have braked using the same force as in normal conditions,
• the second is connected to the psychological fear of the brakes locking even though ABS is fitted.

The device is therefore given the taks of recognizing an emergency situation and consequently increasing the pressure on the system until maximum performance compatible with the vehicle grip limits is produced. The same deceleration is produced through a reduction in the force on the pedal of up to a third compared with normal braking.

In addition to the braking distance, the stopping distance consists of the distance covered both in terms of reaction time and braking response time. By reducing the latter, especially at high speeds, the device is capable of reducing the stopping distance.

Composition

On the Stilo this function is carried out:

• by a mechanical device housed in the brake servo pump unit (E.V.A. Emergency Valve Assistance) on vehicles fitted with ASR
• by a motor on the hydaulic aggregate electronically operated by the ABS control unit (H.B.A. Hydraulic Brake Assistance) on vehicles with ESP.

The E.V.A. device uses the hydraulic reaction of the brake pump to produce a very high assistance ratio in the case of panic braking (the intervention level is linked to the application speed).

H.B.A. is an ESP software module which controls the pressure increase gradient when the driver brakes. A panic situation is recognized when this gradient exceeds the pre-set level.

On both devices the speed threshold is set so that it only intervenes in genuine panic situations without affecting the pedal in normal vehicle usage conditions.

Section of brake servo with conventional pump

1 - Reaction disc

2 - Valve piston

Composition

Section of brake servo with EVA device

1 - Fast ratio piston

2 - Slow ratio piston

3 - Brake pump

4 - EVA device

Function

The yaw/lateral acceleration sensor detects rotations about the vehicle vertical axis (yaw) and measures side accelerations.

It is connected directly to the ABS control unit.

Function

Sensor operational specifications are as follows:

Supply voltage:

• Minimum value 8.2 V
• Maximum value 16V
• Rated value 12V

Operating temperature:

• Minimum value -40°Χ
• Maximum value +85°Χ

Current uptake at 12 V:

• Rated value 70mA

Yaw sensor:

• Measurement range +/-100 °/s
• Resolution +/-0.3°/σ

Side acceleration sensor:

• Measurement range +/-1.8 g

Composition

The sensor consists of a plastic case that encloses the sensitive parts that detect yaw, lateral acceleration and longitudinal acceleration/deceleration and also an electronic control system.

The sensor has a six-pin connector, with all pins connected.

Pin 1, Yaw sensor reference signal

Pin 2, ABS control unit yaw sensor signal

Pin 3, sensor power supply 12V

Pin 4, yaw signal in °/Sec

Pin 5, side acceleration sensor in 'g.'

Pin 6, Earth

Location

The sensor is located at the centre of gravity beneath the central console near the Air Bag control unit.

Operation

The sensor is supplied directly by the ABS control unit and supplies a yaw and acceleration signal simultaneously via its sensitive elements.

The yaw signal is processed directly by the sensor and sent to the ABS control unit with a superimposed reference signal.

Yaw signal range is between:

• lower limit 0.65V
• upper limit 4.35V
• reference signal 2.5V.

1 - Upper limit

2 - Reference signal

3 - Lower limit

Operation

The ABS control unit supplies an alternating signal to the sensor for testing and safety functions.

Function

The steering angle sensor detects steering wheel angle and turning speed and makes the data available to the C-CAN.

Location

The sensor is incorporated in the electric steering motor. The electric steering control unit uses the CAN to pass on the steering angle and steering wheel rotation speed values which are useful for the ESP control unit for the management of the entire system.

Pin out

The electric steering control unit comprises two connectors which have the following connections:

Connector A:

Pin 1, +30 power supply

Pin 2, Earth

Connector B:

Pin 1, +15 ignition-operated power supply

Pin 2, N.C.

Pin 3, N.C.

Pin 4, K diagnostic line

Pin 5, C CAN-L1 connection

Pin 6, C CAN-H1 connection

Pin 7, C CAN-L2 connection

Pin 8, C CAN-H2 connection

Operation

The sensor, integrated in the electric steering motor, measures:

• the steering column angular position
• the steering column rotation speed.

This information is processed and then made available to the brake node via the C-CAN.

The angular measurement range is 780° - -780° ωιτη αν ανγυλαρ ρεσολυτιον οφ 0.1 °.