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Brakes 53
9-5
Electronic Stability Program, ESP (Available on Linear,
Standard on Arc and Aero)
Brief description, ESP
ESP (Electronic Stability Program) is a system
that regulates the engine torque and braking to
assist the driver with stabilizing the vehicle
during unexpected situations that would
otherwise be difficult to handle.
ESP also includes ABS and TCS, which have
the same function as before.
ESP is a development of these two systems with
each function acting individually as well as
together in one control module. A fault in either
the ESP or TCS function will disengage them
both but not the ABS, which will continue to
function unless it is affected by the fault. The
system includes a switch on the dash to shut off
the ESP (and TCS) functions.
When ESP engages during a skid, it will
counteract the skid by braking one or more
wheels without the driver needing to touch the
brake pedal. Engine power can also be reduced
to prevent wheelspin after the ESP control
module requests an engine torque. The engine
control module governs the engine torque
according to this request.
The system receives information from a number
of sensors that measure the wheel speed, side
acceleration, yaw rate, steering angle and brake
pressure. These values are used by the ESP
system control module, which is integrated in the
hydraulic unit. The control module continuously
calculates the course of the vehicle, ACTUAL
VALUE (the direction of the vehicle), and
compares it with the direction determined by the
driver with the steering wheel, DESIRED
VALUE. If the ACTUAL VALUE does not
correspond to the DESIRED VALUE, the system
will intervene as necessary by braking one or
two wheels and limiting the engine torque.
• If the car starts to understeer (when the front
tends to continue straight ahead in a bend),
the inside rear wheel will be braked.
• If the car starts to oversteer (the rear tends
to drift out), the system will engage and brake
the outside wheel until the measured and the
calculated yaw rate correspond.
In the U.S. market, ESP will be standard
equipment on the Aero and Arc models. ESP
will be optional on the Linear model.
Note
The course of the car is compared with the one
determined by the driver with the steering wheel
and, if they do not agree, ESP will be engaged.
The driver must turn the steering wheel to the
correct direction of travel if the system is to be
able to function correctly.
ESP does not mean you can drive faster, but
should be regarded as a safety net for
unexpected situations.
On road surfaces with low friction, it does not
matter much how you turn the steering wheel.
When the lateral forces between the tires and
the road surface are close to zero, it is extremely
difficult to correct the direction of travel of the
car.
Cars with standard chassis equipped with ESP
must not be fitted with a sports chassis because
the ESP system cannot be reprogrammed to
accept it. This feature will be available later
during the model year. If the car chassis is too
stiff, ESP will respond too quickly.