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60 Brakes
9-5
ESP function
ESP is a stabilization system that helps to keep
the vehicle on the right course when cornering,
taking evasive action, braking and accelerating.
The stabilizing effect of the ESP system is based
on calculations made by the control module,
which evaluates information sent from the various
system sensors:
• Wheel speed sensors
• Steering wheel angel sensor
• Yaw rate sensor
• Side acceleration sensor
• Brake pressure sensor
Data from these sensors inform the control
module of the driver's intentions, such as the
direction in which the driver wants to travel, if the
driver is braking, etc. The ESP control module,
which is integrated in the hydraulic unit,
continuously calculates the course of the vehicle
(ACTUAL VALUE) and compares it with the
course chosen by the driver with the steering
wheel (DESIRED VALUE).
1. If the car starts to understeer (when the front
tends to continue straight ahead in a bend),
the measured yaw rate (ACTUAL VALUE)
will be lower than the calculated. The system
will brake the inside rear wheel in the bend
until the measured and the calculated yaw
rate (DESIRED VALUE) correspond with
each other.
2. If the car starts to oversteer (the rear tends
to drift out), the measured yaw rate (ACTUAL
VALUE) will be higher than the calculated.
The system will then brake the outer wheels
until the measured and the calculated yaw
rate (DESIRED VALUE) correspond with
each other.
When the system is activated, it can counteract a
skid by braking one or two of the wheels without
the driver needing to touch the brake pedal. The
system reduces engine torque after an engine
torque request to the engine control module and
applies the brakes on the wheels individually.
The ESP system comprises three different
functions: ABS, TCS and ESP. ABS and TCS
have the same function as earlier. See the
respective description of operation.
The wheel brakes are the most efficient and
fastest way of stopping a spinning wheel, while
engine torque regulation is the smoothest and
most comfortable. These two methods often work
simultaneously.