54 4. CONTROLLER DESIGN OF CYBER-PHYSICAL VEHICLE SYSTEMS
Current
Map
PI
Controller
On/Off
Valve
Wheel
Cylinder
∆P
tgt
P
input
P
w_act
(P
out
)
I
ff
I
fb
I Q
P
w_cmd
∆P
error
∆P
act
+
–
+
–
+
–
+
Figure 4.7: Structural diagram of the CLPDL control algorithm for wheel cylinder pressure
modulation.
Based on the analysis above, by setting constant command values for the relief valve and pump-
motor, the stable upstream pressure for the inlet valve can be derived.
According to the working principle of the pressure-difference-limiting control, the up-
stream pressure for the input valve should be greater than or equal to the current driver braking
intensity. In the developed BBW system, accurate modulation of the coil current is achieved by
the current control chip, whose best working region is from 100–600 mA. us, the optimal
value of the pressure difference is set within the range from 0–4 MPa. A switched coordinated
control strategy for relief valve and pump-motor has been designed, as shown in Fig. 4.8. e
pressure increase mode has two sub-phases, denoted as low and high braking intensity mode,
which can realize the different stable upper stream pressure for inlet valves. is property en-
sures that the current control chip works within its optimal region and that there is enough up
stream pressure for the inlet valves. Hydraulic pump only works in the pressure hold and increase
modes. Because no noise is generated when the valve is controlled by the current method, the
noise is significantly reduced with CLPDL control.
Note that the current command value for relief valves RV_cm1, RV_cmd2, and RV_cmd3,
are different for the brake cylinders in front and rear wheels. However, for the same wheel
cylinder, the relative relationship among the three values is the same, which given by is 0 <
RV_cmd3 < RV_cm1 < RV_cmd2.
4.4 HARDWARE-IN-THE-LOOP TEST RESULTS
In this section, to validate and compare the control performance of the proposed approaches,
the HiL experiments were carried out with the new BBW system designed in Section 4.2. e
dSPACE Autobox serves as a real-time platform, in which the models of vehicle motion, electric
motor and battery are running. Meanwhile, the real braking system including hydraulic circuits,
master and wheel cylinders, a vacuum booster and brake pedal, is equipped in the test bench.
Several key parameters of the models used in tests are listed in Table 4.1.
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