312000764 - 3350E VEHICLE DIRECTION CONTROL SYSTEM VDC/ESP
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 forceFp. Rear axle braking forceA. Distribution curve implemented by the brake systemB. Ideal distribution curveC. Distribution curve implemented by a conventional hydraulic load proportioning valveD. Distribution curve implemented by the EBD functionThe 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 gripS. SlipA. EBD intervention areaA. ABS intervention areaC. ESP intervention area1. Lateral force curve2. Longitudinal force curveAs 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:| Signal | Engine Management Node | Instrument Panel Node | Steering angle sensor (electric steering node) |
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| Engine torque reduction request | X | | |
| Right front wheel speed signal | X | | |
| Left front wheel speed signal | X | | |
| Right rear wheel speed signal | X (1) | | |
| Left rear wheel speed signal | X (1) | | |
| ABS activated | X (2) | | |
| ABS status reading | | X | |
| EBD status reading | | X | |
| Steering angle sensor neutral position | | | X |
(1): for diesel versions(2): for petrol versionsControl unit input signals:| Signal | Engine Management Node | Body Computer Node | Steering angle sensor (electric steering node) | Lateral acceleration/yaw sensor |
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| Engine load signal | X | | | |
| Engine speed signal | X | | | |
| Accelerator pedal position | X | | | |
| Parking brake switch signal | | X | | |
| Steering angle signal | | | X | |
| Steering angle sensor malfunction signal | | | X | |
| Vehicle yaw signal | | | | X |
| Vehicle lateral acceleration signal | | | | X |
| Acceleration/yaw sensor malfunction signal | | | | X |
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 engineUNDERSTEER ON CORNERSThe 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 oppos| ... DATA ERROR - CROPPED TEXT | Ошибка данных - Текст обрезан ... |
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