5.3. ACTIVE STEERING SYSTEM 53
Table 5.1: Comparison between conventional active rear steering and pulse active rear steering
Control Strategy Driver’s Input δ
f
Controller’s Input δ
r
Conventional
active rear steering
Pulsed active rear
steering
10
8
6
4
2
0
0 2 4
Time (s)
Steering Angle (deg)
6 8
10
8
6
4
2
0
0 2 4
Time (s)
Steering Angle (deg)
6 8
10
8
6
4
2
0
0 2 4
Time (s)
Steering Angle (deg)
6 8
10
8
6
4
2
0
0 2 4
Time (s)
Steering Angle (deg)
6 8
et al. proposed a novel pulse active rear steering system (PARS) for improving vehicle yaw sta-
bility [53], as shown in Figure 5.4. e hydraulic-mechanical pulsed steering system is designed
and a model that represents the pulsed steering system characteristics is introduced. e oil
volume sent to the hydraulic cylinders is proportional to the angle of the rotary steering valve,
which is driven by a motor, shown schematically in Figure 5.4b. e steering system can be
represented by a combination of a steering sliding valve and a hydraulic cylinder ram, illustrated
in Figure 5.4b.
5.3.3 FOUR-WHEEL STEERING
Four-wheel steering refers to that four wheels can simultaneously deflect from the vehicle body
according to the signal of the front wheel or the vehicle speed during vehicle steering. When the
steering wheel angle is small, the rear wheel and the front wheel turn in the same direction, this
reduces the turning radius of the vehicle. When the steering wheel angle is large, the rear wheel
and the front wheel turn in the reverse direction, thus the handing stability is improved. Four-
54 5. ACTIVE CONTROL FOR VEHICLE ROLLOVER AVOIDANCE
Hydraulic Steering Actuator
Speed and Direction
Motor
Pump
Rear Pulse Steering Angle
Rotary
Valve
Flow
Meter
Control
Part
Hydraulic Steering Actuator
10
11
13
12
5
4
7
8
9
(a) e implementation of PARS
(b) e schematic of PARS
Figure 5.4: e implementation on a multi-link suspension and the schematic of PARS.
wheel steering can basically maintain the vehicle mass center side-slip angle is zero in the process
of steering and can improve the dynamic response characteristic of the vehicle to steering wheel
input. To a certain extent, the transient response performance indexes of the yaw angular velocity
and lateral acceleration are improved, and the stability of the vehicle at high speed is obviously
improved. At high speed, four-wheel steering system through the same direction of the rear and
front-wheel steering, can effectively reduce/eliminate the vehicle sideslip, and improve vehicle
stability and safety. Ono et al. used 4-wheel-distributed steering and 4-wheel-distributed trac-
tion/braking systems to improve the handing stability of vehicle [54]. e hierarchical control
structure shown in Figure 5.5 is adopted for vehicle dynamics control.
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