125000358 - 3350E VEHICLE DIRECTION CONTROL SYSTEM VDC

CONSTRUCTION SPECIFICATIONS

VIEW OF ASSEMBLY
1 - ABS/VDC control unit2 - Steering angle sensor3 - Engine management control unit4 - Slewing/lateral acceleration sensor5 - Right front wheel sensor6 - ASR off button7 - Right rear wheel sensor8 - Left rear wheel sensor9 - ASR/VDC warning light10 - EBD warning light11 - ABS warning light12 - Left front wheel sensor

SPECIFICATIONS

Function

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 T.C. and A.S.R./M.S.R. systems which control traction during acceleration through action on the brakes (T.C.) and traction/drive torque during acceleration and release through action on the brakes and on the engine control system motorized throttle (A.S.R./M.S.R.).

The V.D.C. system (Vehicle Dynamics Control) includes all the above listed functions ensuring optimum dynamic control of the vehicle with the addition of specific sensors:

  • steering angle sensor on the steering wheel
  • slewing/lateral acceleration sensor at the centre of gravity under the centre tunnel.
µ - Wheel gripS - SlippingA - EBD intervention areaA - ABS intervention areaC - VDC intervention area1 - Lateral force curve2 - Longitudinal force curveAs can be seen from the grip/slipping diagram, the area covered by the VDC system is larger than that covered by a conventional ABS/EBD system.The V.D.C. system cannot be switched off as it is a safety system; the A.S.R./M.S.R. function, on the other hand, can be switched off via the button in the centre console.The intervention of the V.D.C. system is signalled by a special warning light in the instrument panel node (N.Q.S.)

COMPOSITION

Structure

The V.D.C. system consists of:

  • an electro-hydraulic/electronic A.B.S. 5.7 control unit (with a V.D.C. logic)
  • interface with the C-CAN line, in the ABS control unit, for conversing with the engine management control unit, robotized transmission, body computer and steering angle sensor
  • magnetic-resistive type wheel speed sensors
  • steering angle sensor with C.A.N. interface (steering angle sensor)
  • slewing/lateral acceleration sensor in one-piece
  • brake fluid pressure sensor fitted on the A.B.S. control unit
  • ASR/VDC warning light in the instrument panel controlled via the C.A.N. line
  • A.S.R. off switch with a warning light in the button
The N.Q.S. signals that the A.S.R. is switched off through a message in the DOT matrix

OPERATION

General remarks

The V.D.C. system 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 V.D.C. system is entrusted to the Bosch 5.7 type 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 angle/steering wheel rotation speed
  • 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.C.R. (robotized gearbox node) for the management of gear changes
  • 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 VDC at low brake fluid temperatures.The V.D.C. 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).

INPUT SIGNALS:

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

OUTPUT SIGNALS:

  • Brake pressure modulation control (15)
  • Ignition advance reduction control (from C-CAN line) (9)
  • Engine power management control (from C-CAN line) (8)
  • Gear change inhibition (from C-CAN line) (13)
  • Wheel speed signal for speedometer and milometer (from C-CAN) (14)
  • VSO signal (vehicle speed) (14)
  • ASR/VDC warning light in instrument panel control (from C-CAN line) (11)
  • ASR off LED (7)
As stated previously, in addition to controlling the slipping of the vehicle in a lengthwise direction, the VDC 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 increase in 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 go straight, 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. 5.7 control unit must firstly calculate the behaviour of vehicle set by the driver using:

  • steering angle/steering wheel rotation speed 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 can preceive deviations from the trajectory and prevalence of axle drift, and corrects the trajectory with appropriate actions on the brakes and 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
  • partial V.D.C.

V.d.c. intervention display

The intervention of the VDC system is shown by the special warning light in the instrument panel flashing (5 Hz d.c. 50%).
the V.D.C. system improves driving safety but there are limited situations which cannot be controlled by the V.D.C. 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

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