SsangYong Actyon Sports II. Service manual - part 155

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6. SYSTEM DESCRIPTION

1) Block Diagram of ESP HECU

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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?

▶

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

▶

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