184000332 - 3350E VEHICLE DIRECTION CONTROL SYSTEM VDC

SPECIFICATIONS

GENERAL VIEW
1 - ABS/ESP control unit2 - Steering angle sensor (integrated in the electric steering device)3 - Engine management control unit4 - Yaw/lateral acceleration sensor5 - Longitudinal acceleration sensor6 - ASR off button3 - Front right wheel sensor8 - Rear right wheel sensor9 - Rear left wheel sensor10 - Front left wheel sensor11 - ESP/ASR warning light12 - EBD warning light13 - ABS warning light14 - HHC warning light15 - Handbrake switch15 - Reverse switchThe BOSCH 8 ABS currently used is the most advanced available today, offering the best driving safety. To obtain this characteristic, the ESP system, which incorporates the ASR/MSR/HBA/HHC functions, has been added to the ABS/EBD electrohydraulic unit.
μ - Wheel gripS - SlipA - EBD intervention areaB - ABS intervention areaC - ESP intervention area1 - Side force curve2 - Longitudinal force curveAs may be seen from the grip/slip diagram, the ESP system covers a bigger area than a conventional ABS/EBD.The ESP 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/MSR function).

INPUT SIGNALS:

  • Wheel speed sensors (from direct line) (3)
  • Normally open brake pedal sensor (from direct line) (4)
  • Normally closed brake pedal sensor (from direct line) (5)
  • ASR button OFF (from direct line) (6)
  • Engine management control unit (2) (from C-CAN line)
  • Throttle angle position (from C-CAN line NCM) (8)
  • Body computer (14)
  • Handbrake lever position (from C-CAN line) (18)
  • 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)
  • Gradient longitudinal acceleration sensor (X) (from direct line) (17)
  • Steering wheel steering angle/rotation sensor, integrated in electric steering device (from C-CAN line) (12)
  • Robotised gearbox control unit (gear engaged status) (from C-CAN line) (13)
  • Hydraulic system pressure sensor (integrated in ABS/ESP control unit) (1)
  • Reverse engagement sensor (16)

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 on versions with robotised gearbox (from C-CAN line) (13)
  • Wheel speed signal for speedometer and mileometer (from C-CAN line) (14)
  • VSO (vehicle speed) signal (14)
  • ABS/EBD/ASR/ESP/HHC warning light control on panel (from C-CAN line) (11)
  • ASR LED off (7)

ESP SYSTEM

Introduction

The ESP (Electronic Stability Program) is an active safety system for controlling the vehicle in dynamic manoeuvres on the road in emergency conditions.The ESP system recognises the under or oversteer condition, and reduces the yaw fluctuations. The ASR/TC function recognises loss of grip in traction conditions, ensuring maximum acceleration and driveability.This has been obtained by adding specific sensors: steering angle sensor and yaw/lateral acceleration sensor.The ESP system is managed by the ABS electronic control unit 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 sensor/steering wheel rotation speed (integrated in the electric steering device)
  • yaw/lateral acceleration sensors
  • motorised throttle position (from engine management control unit)
  • wheel rpm sensor
  • hydraulic system pressure sensor (integrated in the ABS/ESP control unit)

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; identifying 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:

  • the NCM (engine control node) for torque adjustment,
  • N.C.R. (robotised gearbox node) for gear shift management in versions in which it is fitted
  • NBC (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 flexible 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.

Operating strategies

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 and the situation of the wheel (supporting or unladen) and friction coefficient, which is dependent on ground 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.

Understeer:

  • 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 lateral acceleration. In this case, the car tends to go straight when turning a corner (it tends to take the curve wide).

Oversteer:

  • 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).

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

  • steering angle sensor
  • accelerator pedal position
  • brake pedal pressure

the control unit compares the above parameters with actual vehicle behaviour by means of:

  • vehicle speed sensor (active sensors on the wheels),
  • yaw/lateral acceleration sensor

if the signals deviate from normal vehice operation, 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. 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, wind gusts, car's 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 management.Understeering on cornersThe 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 cornersThe 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. In specific cases, the speed of the drive wheel on the inside of the corner is also increased in addition to the braking action.
The system intervenes before understeer and oversteer reach excessive levels in order to prevent 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 changes in straight trajectory (wind gusts, 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/decelerationThe control unit implements the ASR/MSR strategy controlling the vehicle's side acceleration and thus regulating the action on the brakes and driving torque.Asr/msr exclusion

If the ASR/MSR function is excluded, the following functions remain active:

  • ABS/EBD;
  • TC up to a speed of 40 km/h;
  • ESP with intervention only of brakes.
  • HHC
Esp intervention displayWhen 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.

ASR/MSR FUNCTION

This system carries out all the normal anti-lock and brake distribution functions of the ABS 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 (ASR/MSR) and applying a braking force to one or both drive wheels (TC).If one or both drive wheels tend to slip during acceleration, the ASR system orders the engine control unit to reduce the torque transmitted to the wheels and almost simultaneously brakes the wheel or wheels without the driver having to do anything (TC).If the wheels tend to lock during hard deceleration, the MSR system requests the engine control unit to adjust engine braking torque to prevent car stability.The system can be cut out by activating a button located on the central tunnel near the handbrake lever.The LED on the button comes on and a message is displayed on the instrument panel to indicate deactivation of the ASR/MSR.The button warning light comes on on the control panel to indicate system cut-out due to a fault recorded by the control unit.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 processes the signals coming from the active sensors on the four wheels, the brake light switch and the button for switching the ASR function on/off.It continuously compares the speed of the wheels on the same side of the car (front right with rear right and front left with rear left) and when it detects a difference in speed between the two wheels on the same side of over 2-6 km/h (intervention threshold), it intervenes with the ASR logicThe ABS/ASR control unit communicates continuously with the engine control unit via the C-CAN line.

Drive wheel slippage

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