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2) Operation of ESP System
(1) Under steering
What is understeering? ▶
ESP controls during understeer ▶ 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.
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.
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(2) Over steering
What is oversteering? ▶
ESP controls during oversteer ▶ 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.
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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4. WHEEL ALIGNMENT
▶Toe-in
▶Camber
In automotive engineering, toe, also known as
tracking, is the symmetric angle that each wheel
makes with the longitudinal axis of the vehicle, as
a function of static geometry, and kinematic and
compliant effects. This can be contrasted with
steer, which is the anti-symmetric angle, i.e. both
wheels point to the left or right, in parallel
(roughly). Positive toe, or toe in, is the front of the
wheel pointing in towards the center line of the
vehicle. Negative toe, or toe out, is the front of the
wheel pointing away from the center line of the
vehicle. Toe can be measured in linear units, at
the front of the tire, or as an angular deflection.
Camber is the angle made by the wheels of a
vehicle; specifically, it is the angle between the
vertical axis of the wheels used for steering and
the vertical axis of the vehicle when viewed from
the front or rear. It is used in the design of
steering and suspension. If the top of the wheel
is farther out than the bottom (that is, away from
the axle), it is called positive camber; if the
bottom of the wheel is farther out than the top, it
is called negative camber. Wheel alignment consists of adjusting the angles of the wheels so that they are parallel to each other
and perpendicular to the ground, thus maximizing tire life and ensures straight and true tracking along
a straight and level road.
Camber angle alters the handling qualities of a particular suspension design; in particular, negative
camber improves grip when cornering. This is because it places the tire at a better angle to the road,
transmitting the forces through the vertical plane of the tire rather than through a shear force across it.
Another reason for negative camber is that a rubber tire tends to roll on itself while cornering. Negative
camber can also be caused by excessive weight on the front wheels. This is commonly seen on
modified cars with larger engines than standard; the weight of the modified engine can make the
wheels negatively camber. The inside edge of the contact patch would begin to lift off of the ground if
the tire had zero camber, reducing the area of the contact patch. This effect is compensated for by
applying negative camber, maximizing the contact patch area. Note that this is only true for the outside
tire during the turn; the inside tire would benefit most from positive camber.
