HEXA

ELECTRONIC STABILITY PROGRAM (ESP)

19 ELECTRONIC STABILITY PROGRAM

(ESP)

19.1 GENERAL INFORMATION

NECESSITY OF ESP AND TCS

The road grip available to the vehicle can vary

greatly as a result of road conditions, weather,

tyres etc. Whenever a wheel looses its grip with

the road surface, the vehicles’ stability and

controllability is ultimately affected.

I. TRACTION CONTROL SYSTEM (TCS)

When starting off or accelerating if the driver gives

too much throttle the driven wheels can loose

traction with the road surface. This can occur when

accelerating from stand still on the flat or a hill,

accelerating after a gear change, through a corner

or just by increasing the throttle suddenly on a

slippery road. If the front wheels loose traction the

vehicle will tend to understeer where as if the rear

wheels loose traction the vehicle may tend towards

over steer. This effect can be magnified if available

grip is different for each side of the vehicle.

The primary function of the traction control system

is to prevent the vehicle from entering these

unstable conditions by controlling the vehicles’

longitudinal accelerations and hence enhancing

the driving safety. In addition the TCS by

regulating the optimum slip levels and emulating

the function of a differential lock prevents the

wheels from spinning and increases the traction

capability of the vehicle. This is achieved through a

combination of brake control regulating the torque

being transferred to the road at each driving wheel,

and engine torque management regulating the

amount of torque available.

II. Vehicle Dynamic controller (VDC)

A vehicle can reach it critical limits for many

reasons be it through environmental influences

such as a sudden change in the road surface,

adverse weather conditions, an obstacle appearing

in the road, or making a sudden steering input or

simply due to driving at an inappropriate speed.

When a vehicle reaches it critical limits it can

becomes uncontrollable. Any one of these

conditions could cause the vehicle to yaw about its

axis, and it is in these situations that ESP has

been developed to support the driver by reacting to

the rotational and lateral accelerations of the

vehicle.

The ESP monitors the driver inputs and vehicle

responses through the various sensors when the

system detects that the vehicle is becoming

unstable and no longer following the driver

intended course i.e. starting to under or over steer

it induces a corrective yaw moment to the vehicle

through the application of one of the wheel brakes,

usually combined with a reduction in the engine

torque. ESP is a recognised vehicle safety system

but can only work within the physical limits of the

vehicle and environment, and is not a substitute for

responsible driving.

III. HYDRAULIC BRAKE ASSIST (HBA)

In an emergency braking situation the best

stopping performance will only be reached if the

driver brakes quickly and with sufficient force to

bring all four wheels to ABS control. Research has

shown that while many drivers apply the brakes

quickly in an emergency but often do not apply

sufficient force to achieve the best possible

stopping distance. The function of the Hydraulic

Brake Assist is to detect the emergency brake

application and to boost to the brake pressure

hence enabling a normal driver to achieve the best

possible stop.

Value Added functions configured with ESP 9.1

A. Hill Hold Control

Hill Hold Control is a comfort function. The main

intend is to prevent the vehicle from rolling

backwards while driving off up-hill on an inclined

surface.

B. Hill decent control

HDC is a comfort function, which assists the driver

descending a hill by means of active brake

intervention. Therefore, the vehicle speed is limited

without driver´s help. This function works in both

forward and reverse gear (in reverse gear,

thresholds for operation may vary). Activation and

deactivation of the HDC-function are done by

pressing the HDC button on the dashboard.

A. Roll over mitigation

Rollovers are dangerous incidents and have a

higher fatality rate than other kinds of crashes.

The main feature of the Roll Movement Functions

is the detection of a rollover critical situation, and

to mitigate the vehicle rollover. This function try to

prevent friction-induced roll-over. This is done by

active brake interventions on selected wheels,

thereby reducing the tire side forces that cause a

roll-over situation.