SsangYong Korando III (2010 year). Manual — part 553

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2) Operation of ESP System

The ESP (Electronic Stability Program) has been developed to help a driver avoid danger of losing

control of the vehicle stability due to understeer or oversteer during cornering. The yaw rate sensor,

lateral sensor and longitudinal sensor in the sensor cluster and the steering wheel angle sensor under

the steering column detect the vehicle conditions when the inner or outer wheels are spinning during

oversteer, understeer or cornering. The ESP ECU controls against oversteer or understeer during

cornering by controlling the vehicle stability using input values from these sensors and applying the

braking force to the corresponding wheels independently. The system also controls the engine power

right before the wheel spin synchronized with the ASR function to decelerate the vehicle automatically in

order to maintain the vehicle stable during cornering.

(1) Under steering

What is understeering?

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Understeer is a term for a condition in which the steering wheel is steered to a certain angle during driving

and the front tires slip toward the reverse direction of the desired direction. Generally, vehicles are

designed to have understeer. It is because that the vehicle can return back to inside of cornering line

when the steering wheel is steered toward the inside even when the front wheels are slipped outward.

As the centrifugal force increases, the tires can easily lose the traction and the vehicle tends to slip

outward when the curve angle gets bigger and the speed increases.

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ESP controls during understeer

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The ESP system recognizes the directional angle with the steering wheel angle sensor and senses the

slipping route that occurs reversely against the vehicle cornering direction during understeer with the yaw

rate sensor and lateral sensor. Then, the ESP system applies the braking force to the rear inner wheel to

compensate the yaw moment value. In this way, the vehicle does not lose its driving direction and the

driver can steer the vehicle as intended.

(2) Over steering

What is oversteering?

▶

Oversteer is a term of a condition in which the steering wheel is steered to a certain angle during driving

and the rear tires slip outward losing traction.

Compared to understeering vehicles, it is hard to control the vehicle during cornering and the vehicle can

spin due to rear wheel moment when the rear tires lose traction and the vehicle speed increases.

ESP controls during oversteer

▶

The ESP system recognizes the directional angle with the steering wheel angle sensor and senses the

slipping route that occurs towards the vehicle cornering direction during oversteer with the yaw rate

sensor and lateral sensor. Then the ESP system applies the braking force to the front outer wheel to

compensate the yaw moment value. In this way, the vehicle does not lose its driving direction and the

driver can steer the vehicle as intended.

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3) Vehicle Control During Cornering

The figure below shows the vehicle controls by the ESP system under various situations such as when

the brake pedal is depressed or not depressed during cornering, when the ABS is operating and when

braking without the ABS. It also includes the vehicle conditions when the TCS, a part of the ESP system,

is operating.

Condition

Understeer control

Oversteer control

Only ESP in

operation

No braking by driver

ESP

+

Normal braking

(no ABS operation)

ESP

+

ABS brake

ESP + ASR

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4) HBA (Hydraulic Brake Assist System)

(1) Purpose

HBA (Hydraulic Brake Assist) system helps in an emergency braking situation when the driver applies

the brake fast, but not with sufficient pressure, which leads to dangerously long braking distance. ECU

recognizes the attempt at full braking and transmits the signal calling for full brake pressure from the

hydraulic booster. An inexperienced, elderly or physically weak driver may suffer from the accident by not

fully pressing the brake pedal when hard braking is required under emergency. The HBA System

increases the braking force under urgent situations to enhance the inputted braking force from the driver.

Based on the fact that some drivers depress the brake pedal too soft even under when hard braking is

necessary, the HECU system is a safety supplementary system that builds high braking force during

initial braking according to pressure value of the brake pressure sensor and the pressure changes of the

pressure sensor intervals. When the system is designed to apply high braking force when brake pedal is

depressed softly by an elderly or physically weak driver, the vehicle will make abrupt stopping under

normal braking situation due to high braking pressure at each wheels.

(2) Operation

The brake pressure value and the changed value of the pressure sensor are the conditions in which the

HBA System operates. There are 2 pressure sensors under the master cylinder. When the ESP ECU

system determines that emergency braking is present, the pump operates, the brake fluid in the master

cylinder is sent to the pump and the braking pressure is delivered to the wheels via the inlet valves . If the

drive depress the brake pedal slowly, the pressure change is not high. In this case, only the conventional

brake system with booster is activated.

(3) Operating conditions

Sensor pressure: over 40 bar

Pressure changes: over 850 bar/sec

Vehicle speed: over 30 km/h

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