Page 310 - Automotive Engineering Powertrain Chassis System and Vehicle Body

Tyres and wheels C HAPTER 10.1

Fig. 10.1-37 Tyres are only able to transfer a lateral force F Y,V
acting on the vehicle if they are rolling at an angle to the vehicle.
Fig. 10.1-39 Increasing lateral forces F Y,W during cornering
Regardless of whether these are F Y,V or the centrifugal force F C,Y
during cornering, the lateral forces F Y,W should be regarded as caused by the centrifugal force F c , V leads to increasing slip angles a.
being perpendicular to the wheel centre plane.

v in m/s and the radius of the bend R in m, on which the and
vehicle centre of gravity V (Fig. 10.1-29a) moves. With X X
the total weight m v,t of the vehicle the equation is: F Y;W ¼ m Y;W F Z;W ¼ m Y;W F Z;V;t
2
F c;V ¼ m V;t v =R ¼ m V;t a y ¼ F Y;V ðNÞ Together the two equations give:
(10.1.8)
m Y;W F Z;V;t ¼ m Y;W m V;t g ¼ m V;t a y (10.1.9)
The centrifugal or disturbance force is just as large as the
lateral forces on the wheels (Fig. 10.1-37): and
m ¼ g=a y
F Y;V ¼ F Y;W;f;o þ F Y;W;f;i þ F Y;W;r;o þ F Y;W;r;i Y;W
X
¼ F Y;W The coefficient of friction m Y,W is not dependent on the
radius of the curve and driving speed and is therefore
(10.1.8a)
more suitable for calculating cornering behaviour.
The faster the vehicle negotiates a bend, the higher
the coefficient of friction used and the greater the slip
angles (Fig. 10.1-39).

10.1.8.2 Self-steering properties
of vehicles

The self-steering properties of a vehicle describe the
lateral force and hence slip angle ratios produced during
steady-state cornering (radius and driving speed con-
stant; no external disturbances). In the case of an
understeering vehicle, a larger slip angle is required on
the front axle than at the rear axle (a f > a r , Fig. 10.1-41).
During cornering with an increase in lateral acceleration,
the driver must force the vehicle into the bend by in-
Fig. 10.1-38 The higher the lateral force F Y, W , the greater the tyre creasing the steering angle (see Fig. 10.1-2). If the nec-
slip angle a. essary slip angles on the front and rear axles are the same

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