152656 - Operation

General remarks

The ESP continuously recognizes a 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 management of the ESP system is entrusted to the A.B.S. electronic control unit, integrated with a special electro-hydraulic control unit, that allows action on the braking system independently of the action of the user.The control unit processes the following signals:

• steering wheel rotation angle
• lateral acceleration and slewing
• motorized throttle position
• 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:

• N.C.M. for drive torque adjustment,
• N.B.C. (Body Computer Node) for the transmission of the vehicle speed and the control of the warning lights.

The exchange of information between these components takes place via the C-CAN and B-CAN lines.There is a dedicated line (line K) for the diagnosis of the system.The system is combined with a power unit with a specific brake pump; in addition, the pipes between the brake pump and the A.B.S. control unit have a Titaflex insert because the diameter of the pipe (6mm) is larger than regular pipes (4 mm); this is designed to prevent adverse effects on the operation of the ESP at low brake fluid temperatures.The ESP system switches on automatically when the vehicle is started up and cannot be switched off by the user; the button in the centre console only switches off the A.S.R. function and only when advisable (see A.S.R. system).

OPERATING LOGICS

As stated previously, 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 depends on the reaction of the tyres to lateral forces and the adhesion force of the wheel with the road surface.It should be remembered that the adhesion force of a wheel depends on the vertical load which depends on the situation the wheel finds itself in (resting or no load) and on the friction coefficient which depends on the road surface and tyre conditions.When the vehicle is travelling in a straight line, the lateral forces do not really have an effect unless outside factors that increase its intensity intervene (e.g. a gust of wind or a change to a different surface), unlike when driving round a bend where there is a strong increase in lateral forces due to the centrifugal force.The action of the lateral forces produce 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 effect the load on the wheel differs depending on 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 or the outer wheels and lightening of the inner wheels)
• accelerating/decelerating round a bend (combination of the cases mentioned above).

It is obvious that if the lateral forces acting on the individual wheels vary, there will also be a variation in the forces acting on the vehicle axles; consequently the lateral forces acting on the front axle overcome those on the rear axle and viceversa determining a rotation (moment0 on the vehicle axis of the vehicle (slewing axis).The moment of slewing affects the behaviour of the vehicle producing either understeer or oversteer.Understeer for a vehicle is defined as the drift angle of the front axle increasing, during increasing lateral acceleration, greatly compared with that of the rear axle. In this case, when the vehicle is driving round a bend, it will tend to go straight (take the bend wide).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 "do an about-face" (the rear axle tends to move to the outside of the bend, therefore the vehicle "hugs" the bend).In order to keep the effect of lateral forces under control and limit the slewing moment, the A.B.S. 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
• slewing sensor

As can be deduced from what has been said earlier, the control unit is capable of:

• detecting actions carried out by the user, in effect, 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 to incorrect manoeuvres by the user, etc., in order to identify the moment of slewing and the lateral sliding of the axles via the sensors on the four wheels and the slewing/lateral acceleration sensor.

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

Understeer round bends

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 round bends

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 opposite slewing 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.

Sharp variations from the straight path (slalom/overtaking)

In the case 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.

Sharp variation from the straight path (driving on 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.

Sharp acceleration/deceleration

The control unit uses the A.S.R./M.S.R. strategy also controlling the lateral acceleration of the vehicle and, as a result, regulating the action on the front and rear brakes and on the engine torque in a more complete way than on vehicles with ASR only.

A.S.R. exclusion

If the A.S.R./M.S.R. is excluded, the following functions remain activated:

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

ESP intervention display

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

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 the safety of the vehicle.

Diagnostic functions

The ABS control unit is capable of carrying out the autodiagnosis of the system and, in the case of a fault, can:

• deactivate the entire system
• partly deactivate the syste (maintaining the ABS/EBD function).

Below is a list of the faults that can be detected by the control unit, the status of the warning lights and the type of recovery used.

Error	ABS warning light	EBD warning light	ESP warning light	Recovery
Right front sensor electrical error	ON	OFF	ON	R3
Left front sensor electrical error	ON	OFF	ON	R3
Right rear sensor electrical error	ON	OFF	ON	R3
Left rear sensor electrical error	ON	OFF	ON	R3
Right front sensor error	ON	OFF	ON	R3
Left front sensor error	ON	OFF	ON	R3
Right rear sensor error	ON	OFF	ON	R3
Left rear sensor error	ON	OFF	ON	R3
Right front ABS discharge valve	ON	ON	ON	R2
Right front ABS pressurizing valve	ON	ON	ON	R2
Left front ABS discharge valve	ON	ON	ON	R2
Left front ABS pressurizing valve	ON	ON	ON	R2
Left rear ABS discharge valve	ON	ON	ON	R2
Left rear ABS pressurizing valve	ON	ON	ON	R2
Right rear ABS discharge valve	ON	ON	ON	R2
Right rear ABS pressurizing valve	ON	ON	ON	R2
Main valve 1 (VLV1)	ON	ON	ON	R2
Main valve 2 (VLV2)	ON	ON	ON	R2
Operating valve 1 (USV1)	ON	ON	ON	R2
Operating valve 2 (USV2)	ON	ON	ON	R2
Pump motor	ON	OFF	ON	R3
Valve relay	ON	ON	ON	R2/R5
NA NC brake light switch	ON	OFF	ON	R3
L

... DATA ERROR - CROPPED TEXT | Ошибка данных - Текст обрезан ...