52 5. ACTIVE CONTROL FOR VEHICLE ROLLOVER AVOIDANCE
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
-0.2
-0.4
-0.6
-0.8
-1.0
-1.2
-1.4
0 1 2 3 4 5 6 7 8 9 10
Time (s)
Rollover Coefficient
Tires Lift Up
Tires Lift Up
Dangerous Area
Safe Area
Dangerous Area
Figure 5.3: Rollover coefficient estimator for a double-lane change maneuver.
5.3.1 ACTIVE FRONT STEERING CONTROL
e active front steering control is to increase or decrease the steering angle of the front wheel
under the premise of the steering angle controlled by the driver according to the driving state of
the vehicle, thus improving the maneuverability and stability of the vehicle.
5.3.2 PULSE ACTIVE REAR STEERING
e pulse active rear steering (PARS) system focuses on reducing the likelihood of vehicle
rollover by sending steering pulses to a single rear wheel whenever a rollover coefficient is out-
side a predetermined range. e system provides extra steering with respect to a current steering
input from the driver until the rollover coefficient ultimately drops into safe area, as shown in
Figure 5.3.
Table 5.1 shows the key differences between the conventional active rear steering and
PARS. As can be seen, the concept of applying a series of pulses is similar to the standard
commercial anti-lock braking system (ABS). e PARS system is a simple, inexpensive, and
lightweight component that can be added to the vehicle when the vehicle already has ABS.
Sensors for ABS can be simultaneously used to obtain the various measurements for this sys-
tem. In addition, the system can be used in conjunction with other stability or yaw control or
rollover control systems such as differential braking systems. e PARS system consists of two
main parts: a pulse-generating device and a switch controller. e generated pulses provide the
controller’s steering input which, together with the drivers steering input, helps to control the
vehicles rollover. e switch controller includes a rollover estimator that calculates the rollover
coefficient of the vehicle; it is only activated when the potential for rollover is detected. Zhang
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