VEHICLE DIRECTION CONTROL SYSTEM VDC/ESP

Description 3350E

1.2 8v, 1.3 Multijet, 1.4 16v

Specifications

The ABS control unit implements the ABS and EBD functions.

The ABS control unit is connected to the front wiring; the system cable loom is incorporated in the engine compartment cable loom.

The ABS consists of:

• an electronic control unit integrated into the hydraulic control unit;
• an electrohydraulic control unit that modulates braking pressure by means of eight solenoids, two for each wheel;
• four active magnetoresistant sensors that detect the angular speed of rotation of the wheels;
• wiring with specific connector.

For further details, refer to:

See descriptions 3340A ABS CHECK/ADJUSTMENT DEVICES

Operation

The ABS control unit processes the following signals:

• steering angle/steering wheel rotation speed sensor
• yaw/lateral/longitudinal acceleration sensor
• motorized throttle position
• wheel rpm sensors
• hydraulic braking system pressure sensor.

Using these figures, the system interprets the effective dynamics of the vehicle; having identified all the critical conditions resulting from environmental factors (e.g. surface with poor grip) or any errors made by the user (e.g. panic situations) and with subsequent intervention on the brakes and the drive torque, the vehicle is restored to good driving conditions.

The information exchange between the different system components (NCM, NBC, NYL, NFR) is transmitted via the CAN. The system is diagnosed via the CAN.

The system is combined with a power unit with a specific brake pump; in addition, the pipes between the brake pump and the ABS control unit have a larger diameter (6 mm) than normal pipes (4 mm); this is designed to prevent adverse effects on the operation of the ESP at low brake fluid temperatures.

Ebd function (electronic brake-force distribution)

The EBD function controls the distribution of brakeforce and therefore replaces the conventional mechanical load proportioning valve to allow:

• independent action on the rear brake callipers;
• improved brakeforce distribution;
• optimum intervention under any load condition (static or dynamic), driving conditions (in a straight line or corner) and when the vehicle is in any state of repair (worn tyres, brakes and suspension);
• implementation of a strategy that follows the ideal distribution curve.

Fa. Front axle braking force

Fp. Rear axle braking force

A. Distribution curve implemented by the brake system

B. Ideal distribution curve

C. Distribution curve implemented by a conventional hydraulic load proportioning valve

D. Distribution curve implemented by the EBD function

The failure of the EBD function is signalled by the insufficient brake fluid and/or handbrake applied warning light coming on.

Under these conditions, the car must be driven with extreme caution to the nearest authorised workshop to check the system.

Specifications

Driving a vehicle in all conditions where the physical limits of grip and, consequently, stability may be reached can be a difficult task for the average driver. Therefore, in order to further improve safe driving conditions, an electronic system capable of assisting the driver with this difficult task is available.

The systems currently employed to ensure safer driving in particular conditions are mainly the A.B.S. which controls braking and the systems which control traction during acceleration through action on the brakes and traction/drive torque during acceleration and release, through action on the brakes and on the engine control system motorized throttle (MSR).

The ESP system includes all the above-listed functions, ensuring optimum dynamic control of the vehicle with the addition of specific sensors:

• steering angle sensor located inside the electric steering (electric steering node, NGE);
• yaw/lateral acceleration sensor at the centre of gravity under the centre console (handbrake area).

µ. Wheel grip

S. Slip

A. EBD intervention area

A. ABS intervention area

C. ESP intervention area

1. Lateral force curve

2. Longitudinal force curve

As can be seen from the hold versus slip graph, the area covered by the ESP system is larger than that covered by a conventional ABS/EBD system.

The intervention of the ESP system is signalled by a special warning light in the instrument panel.

Esp function (electronic stability program)

Composition

The ESP system consists of:

• specific ABS electrohydraulic/electronic control unit;
• interface with the CAN line, resident in the ABS control unit for communication with the engine management control unit, steering angle sensor and lateral acceleration sensor;
• magnetoresistant wheel speed sensors;
• steering angle sensor with CAN interface (electric steering node);
• yaw/lateral acceleration sensor in one piece with the CAN interface;
• brake fluid pressure sensor incorporated in the A.B.S. control unit;
• ABS-EBD-ESP warning light in the instrument panel controlled via the B-CAN line.

Operation

The ESP continuously recognizes loss in grip for the wheels, both longitudinal and transverse, in all driving conditions from braking to acceleration in order to ensure the direction and the stability of the vehicle.

The ESP system is managed by the ABS electronic control unit, integrated with a special electro-hydraulic control unit that allows action on the braking system independent of the user''s action.

The control unit processes the following signals:

• steering wheel rotation angle;
• lateral acceleration and yaw;
• engine operating conditions;
• wheel rpm;
• hydraulic braking system pressure

and uses special algorithms in the electronic control unit software to obtain the figures for the dynamic control of the vehicle:

• longitudinal and transverse sliding between the wheels and the road surface;
• axle drift.

Using these figures the system interprets the effective dynamics of the vehicle; having identified all the critical conditions due to environmental factors (e.g. surface with poor grip) or any errors made by the user (e.g. panic situations) and with subsequent intervention on the brakes and the drive torque, the vehicle is restored to good driving conditions.

The system interfaces with:

• Engine Management Node for drive torque adjustment via the C-CAN line;
• Instrument panel node via the B-CAN line for warning lights control.

The ESP system comes on automatically when the vehicle is started and cannot be turned off.

Control unit output signals:

(1): for diesel versions

(2): for petrol versions

Control unit input signals:

Operating strategies

In addition to controlling the slipping of the vehicle in a lengthwise direction, the ESP system also controls slipping in a sideways direction and, as a result, controls the lateral stability of the vehicle.

The lateral stability of a vehicle is the result of the reaction of the tyres to lateral forces due to increased centrifugal force.

The action of the lateral forces produces a variation in the drift angle of the wheels and, consequently, a variation in the axle drift (drift angle = difference between the desired route and the effective route).

The lateral forces do not, however, act equally on all four wheels because they are not subject to the same load conditions. In fact, the load on the wheel differs according to the situation the wheel is in, namely:

• acceleration (lightening of the front axle and loading of the rear axle);
• braking (loading of the front axle and lightening of the rear axle);
• bend to the right/left (loading of the outer wheels and lightening of the inner wheels);
• accelerating/decelerating round a bend (combination of the cases mentioned above).

If the lateral forces acting on the individual wheels vary, there will evidently also be a change in the forces acting on the vehicle axles; consequently the lateral forces acting on the front axle take precedence over those acting on the rear axle and viceversa, determining a rotation (moment) on the vehicle''s vertical axis (yaw axis).

The yaw moment affects the behaviour of the vehicle, producing either understeer or oversteer.

Understeer for a vehicle is when, with increasing lateral acceleration, the drift angle for the front axle increases greatly compared with that of the rear axle. When this happens, the vehicle tends to go straight ahead (taking the curve wide) when cornering.

Oversteer for a vehicle is when, with increasing transverse acceleration, the drift angle for the rear axle increases greatly compared with that of the front axle. In this case the vehicle tends to turn around on itself (the rear axle tends to go straight, making the vehicle cut off the corner).

In order to keep the effect of lateral forces under control and limit the yaw moment, the ABS control unit must firstly calculate the behaviour of vehicle set by the driver, using:

• steering wheel angle sensor;
• accelerator pedal position;
• brake circuit pressure;

after which the control unit should check the actual behaviour of the vehicle through:

• the wheel sensors (vehicle speed/wheel speed);
• lateral acceleration sensor;
• yaw sensor.

The control unit is capable of:

• detecting actions carried out by the user; through the position of the steering wheel, it checks the number of degrees (wide radius or narrow radius bends) and the speed for rotating the steering wheel (sharp or gentle rotations) and, using the position of the throttle and the brake pressure when accelerating or braking, how the user is taking the bend or deviating from the straight path.
• detecting the actual behaviour of the vehicle given the environmental variables (e.g. slippery surface), reaction of the vehicle, incorrect manoeuvres by the user, etc., in order to identify the yaw moment and the lateral sliding of the axles via the sensors on the four wheels and the yaw/lateral acceleration sensor.

These two operations are necessary in order to superimpose the mathematical model mapped in the control unit on the effective behaviour of the vehicle, to identify the state in which the vehicle is in (understeer or oversteer) and to decide the action for the brakes and the engine

UNDERSTEER ON CORNERS

The control unit verifies the presence of understeer (mainly from the drift of the front axle), corrects the behaviour of the vehicle, braking the inner wheels round the bend in order to create an opposing moment which will lead the vehicle towards the centre of the bend and, possibly, reducing the drive torque.

OVERSTEER ON CORNERS

In the presence of understeer (mainly from the drift of the rear axle) the control unit corrects the behaviour of the vehicle, braking the outer front wheel round the bend in order to create an opposing yaw moment, if necessary increasing the drive torque.

The system intervenes before the oversteer and understeer values are too high in order to limit the corrective measures that have to be taken, which could make handling difficult.

ABRUPT VARIATIONS FROM A STRAIGHT PATH (SLALOM/OVERTAKING)

In the event of sharp variations from the path (e.g. overtaking, slalom), the control unit identifies possible oversteer and understeer conditions and corrects the path of the vehicle, acting as described in the cases mentioned previously.

ABRUPT VARIATION FROM A STRAIGHT PATH (DRIVING OVER DIFFERENT SURFACES)

The control unit is capable of detecting deviations in the path and the prevalence of axle drift, correcting the path through suitable action on the brakes and the engine.

INTERVENTION IN CONDITIONS WHERE ROAD SURFACE GRIP IS GOOD (ASPHALT)

For petrol versions:

Engine management control unit torque reduction through variation in the ignition advances.

A further reduction in torque through a decrease in the throttle opening (by the engine management control unit through the motorized throttle body).

Hydraulic system intervention (braking force on drive wheels).

For JTD versions:

Reduction in torque by means of engine management control unit through a decrease in the fuel flow rate.

Hydraulic system intervention (braking force on drive wheels).

OPERATION IN POOR GRIP CONDITIONS

The system is capable of recognising these conditions by comparing the acceleration of the drive wheels with the torque transmitted by the engine (engine load from the engine management control unit).

The system behaves as if both drive wheels were slipping in road surface conditions with good grip (asphalt).

INTERVENTION IN THE EVENT OF ONE DRIVE WHEEL ONLY SLIPPING

For petrol versions:

Engine management control unit torque reduction through variation in the ignition advances.

A further reduction in torque through a decrease in the throttle opening (by the engine management control unit through the motorized throttle body).

Hydraulic system cuts in, a braking action is exerted on the wheel that is slipping to guarantee the differential a resistant force on the side with poor grip. This resistive force allows the differential to transmit an equal torque with good grip.

For JTD versions:

Reduction in torque by means of engine management control unit through a decrease in the fuel flow rate.

hydraulic system cuts in, a braking action is exerted on the wheel that is slipping to guarantee the differential a resistant force on the side with poor grip. This resistive force allows the differential to transmit an equal torque with good grip.

Esp intervention display

The intervention of the ESP system is shown by the flashing of the special warning light on the instrument panel (5 Hz d.c. 50%).

Fault signals

If a fault occurs, the ESP system will automatically switch off and the associated warning light on the instrument panel comes on with a fixed light, together with the message on the reconfigurable multifunction display (where supplied) and the illumination of the LED on the ASR OFF button.

The ESP system improves driving safety but there are limited situations which cannot be controlled by the ESP system. Therefore it is not seen as a device which improves the performance of the vehicle but as a device that improves its safety.

Operation of the hydraulic system

The electrohydraulic unit on the versions equipped with ASR has 4 additional solenoids.

When the (normally closed) intake solenoid is activated, the additional quantity of fluid required to increase the pressure and brake the wheel(s) can be received.

When the (normally open) control solenoid is activated it allows the modulated pressure produced by the pump, necessary for the intervention of the ESP, to be maintained in the brake calliper-pump circuit.

With the brake pedal pressed, the electronic control unit:

• does not supply the (N.C.) intake solenoid valve (2).
• does not supply the (N.O.) control solenoid (3).

In this way the system operates during the following stages:

• pressure increase
• pressure maintenance
• pressure reduction
• pressure increase and resupply,
• like the ABS EBD system.

1. Pump

2. Intake solenoid valve

3. Control solenoid valve

4. Brake callipers

5. Discharging solenoid valve

6. Charging solenoid valve

When the ESP function is switched on, the electronic control unit:

• supplies hydraulic pump (1)
• supplies (N.C.) intake solenoid valve (2)
• supplies (N.O.) control solenoid (3).

Therefore the pressure produced by pump (1) reaches the brake calliper and is modulated, on the request of the electronic control unit, by discharging solenoid (5) and charging (6) solenoid.

1. Pump

2. Intake solenoid valve

3. Control solenoid valve

4. Brake callipers

5. Discharging solenoid valve

6. Charging solenoid valve

Hba function

It has been demonstrated that in emergency conditions not all drivers manage to produce the best possible performance from their vehicle''s braking system. In effect, although many manage to apply the brakes quickly, the force applied is limited.

The same vehicle deceleration is produced with this function and a load reduced by a third compared with normal braking. In addition, as is known, vehicle stopping distances depend not only on the braking distance but on the distance travelled during the braking reaction time and rest time. By reducing the latter, the device allows the stopping distance to be reduced, especially at high speeds.

Operation

The HBA function (Hydraulic Brake Assist) is carried out by the ABS control unit using ESP software, which controls the oil pressure uphill gradient when the brake is pressed.

Emergency braking conditions are recognised when this gradient exceeds the set level. The device''s speed level is set so that it only intervenes in actual emergency conditions without affecting in any way the manoeuvrability of the pedal in normal vehicle usage conditions.

Hhc function

The HHC function (Hill Holder Control) is designed to assist the driver during departures in forward gears or reverse when the gradient of the road is more than 2%.

The function is incorporated into the ESP system and is automatically activated under the following conditions:

• uphill: vehicle stationary on a road with a gradient of more than 2%, engine on, clutch and brake pedals pressed and gearbox in neutral or gear other than reverse engaged;
• downhill: vehicle stationary on a road with a gradient of more than 2%, engine on, clutch and brake pedals pressed and reverse gear engaged.

During take off the ESP system control unit maintains the braking pressure at the wheels until the engine torque required for departure is reached or for a maximum of 2 seconds, allowing your right foot to be moved easily from the brake pedal to the accelerator.

When 2 seconds have elapsed, without any departure having taken place, the system is automatically deactivated, gradually releasing the braking pressure. During this release stage it is possible to hear a typical mechanical brake release noise, indicating the imminent move of the car.

Fault signals

Any fault in the system is signalled by the dedicated warning light in the instrument panel coming on together with the message shown on the reconfigurable multifunction display (where fitted).

The Hill Holder system is not a parking brake, therefore do not leave the car without activating the handbrake, switching off the engine, and engaging first gear.

Warning light operation

There are 3 warning lights in the instrument panel controlled by the ESP electronic control unit

1. Insufficient brake fluid, handbrake applied warning light (red)

2. Anti-lock brake system warning light (ABS) (amber)

3. ESP system fault, Hill Holder fault warning light (amber)

Insufficient brake fluid/handbrake applied

Turning the key to the MAR (ON) position illuminates the warning light, but it will switch off after a few seconds.

The warning light comes on when:

• the brake fluid level in the reservoir drops below the minimum level, due to a possible fluid leak in the circuit;
• the handbrake is applied.

On some versions there is also an associated acoustic warning sound if the car is moving.

On some versions the display shows the associated message.

If the warning light comes on when the car is in motion, check that the handbrake is not on.

Abs system fault

Turning the key to the MAR (ON) position illuminates the warning light, but it will switch off after a few seconds.

The warning light comes on when the system is not working properly or is not available. In this case the braking system maintains its own unaltered efficiency but without the advantage of the ABS system.

On some versions the display shows the associated message.

Ebd fault (red) (amber)

The simultaneous illumination of warning lights (1) and (2) with the engine running indicates a fault in the EBD system or that the system is not available; in this case sudden braking could cause the rear wheels to lock at an early stage, possibly causing the car to skid.

On some versions the display shows the associated message.

Esp system fault/hill holder fault (amber)

ESP system fault

Turning the key to the MAR (ON) position illuminates the warning light, but it will switch off after a few seconds.

If the warning light does not switch off or remains lit with the led on the ASR OFF button lit while the car is in motion, this means that there is a fault in the ESP system.

The display shows the associated message.

Flashing of the warning light while driving indicates the action of the ESP system.

Hill Holder fault

Turning the key to the MAR (ON) position illuminates the warning light, but it will switch off after a few seconds.

Illumination of the warning light indicates a fault in the Hill Holder System.

The display shows the associated message.

The control unit activates the warning lights according to the following logic:

(1) the system switches off when the key is turned to Stop; every time the key is turned to the MAR position, the system automatically switches on again.

(2) ESP operation limited to operation on the brakes.

DESCRIPTION OF COMPONENTS

Electrohydraulic unit

The unit consists of an electronic control unit (1) and an electro-hydraulic control unit (2).

The hydraulic control unit with ESP includes a sensor for monitoring the braking pressure, which cannot be replaced on its own.

Electronic control unit

The electronic control unit carries out the following functions:

• acquiring the data coming from the wheel active sensors,
• acquiring lateral acceleration and yaw data from the lateral acceleration sensor,
• memorising the control parameters defined during the vehicle P.D.I.,
• memorising the control software,
• processing the data acquired,
• controlling the braking process,
• detecting faults in the ABS/ESP components,
• memorising the fault codes and activating the ABS, ESP and EBD warning lights,
• transmitting and receiving data via the C-CAN line,
• sends and receives data through the diagnostic connector.

ABS/ESP control unit pin out

Hydraulic control unit

It modulates the pressure of the fluid at the brake callipers via the solenoids, with the following operating stages:

• brake fluid pressure increase,
• brake fluid pressure maintenance,
• brake fluid pressure decrease.

For more details see:

See descriptions 3340 ANTI-LOCK BRAKING SYSTEM (ABS)

The hydraulic control unit consists of:

• eight 2-way solenoid valves,
• a dual circuit scavenging pump,
• two low pressure accumulators,
• two high pressure accumulators.

1. Brake servo brake pump unit

2. Hydraulic control unit

3. Left rear wheel

4. Right front wheel

5. Left front wheel

6. Right rear wheel

Active sensors

Specifications

The adoption of active sensors offers the following advantages:

• less sensitivity to the distance between the sensor and the magnetic ring (gap),
• a reduction in sensitivity to electro-magnetic interference,
• the capacity of the active sensor to measure wheel rpm speeds down to zero (instead of 2.5 km/h for passive sensors),
• a saving in weight and size,
• a simplification of the transmission couplings through the elimination of the phonic wheels.

Composition

Active sensors consist of two fundamental components:

• a multipolar magnetic coding device (1) incorporated in the wheel hub bearing (complete with controls)
• a Hall effect receiver (2) that faces the coding device.

The active sensor functions on the basis of variation in the internal electrical resistance, according to the intensity and direction of the lines of force of an external magnetic field (multipolar magnetic coding device). It produces a variable square wave signal whose frequency varies according to the rotation speed of the wheel, but has a constant amplitude.

1. Magnetised sealing ring

2. Bearing

3. Sensor head

4. Active sensor

5. Sealed connector

The active sensor is therefore a proximity sensor with built-in electronic system, connected by means of a cable to the ABS control unit, from which it receives an electrical supply and to which it transmits the speed of the vehicle.

The phonic wheel is a multipolar ring, an elastomer with a certain amount of magnetic particles which are aligned to form different magnets with alternating North / South polarity in a circumferential arrangement by means of a special magnetisation technique. 48 negative poles and 48 positive poles are present in total.

1. Receiver

2. Hall sensor

3. Sensitive elements

4. Multipolar magnetic coding device

5. ABS control unit

6. Sensor power supply

7. Sensor signal

8. Square wave signal generator

9. ABS control unit processor

Steering angle sensor

The steering angle sensor is built into the NGE (electric steering node) and measures the angles in degrees and the rotation speed of the steering wheel and makes these figures available on the CAN.

Lateral acceleration/yaw sensor

The yaw/lateral/longitudinal acceleration sensor is a node designated NYL (lateral yaw node). It detects rotation about the vehicle''s vertical axis (yaw or centrifugal force) and measures lateral and longitudinal accelerations (the latter in order to assess vehicle gradient for the HHC function).

Connection to the ABS/ESP control unit is via the C-CAN. The NFR carries out the associated diagnosis.

Yaw sensor pin out

The sensor is located in a barycentric position at the vehicle earth, under the parking brake lever. It is equipped with a six-pin connector, with all pins connected.