# Development of Proportional Pressure Control Valve for Hydraulic Braking Actuator of Automobile ABS
## 4 Design and Test of Proportional Valve
### Single Proportional Valve Test  
This test is to confirm that the proportional solenoid energy is powerful enough to achieve the desired pressure relief of the proportional valve and that it could be used to control the brake calipers. When the input voltage is different, the armature can obtain a corresponding magnetic attraction and then drive the valve port to open. The single proportional valve test rig is shown in Figure 19a. To confirm the ability of relief, the high pressure of input port is compared with the pressure on the caliper port.  
The experimental procedure of the proportional valve system is described and shown in Figure 19b. The system circuit is pressurized to 175 bars with a hand pump. The PC-based control unit includes an experimental software program, a pressure sensor, an AD/DA interface card and a PWM drive circuit. The control signals are computed in the PC-based control unit, and that drives the proportional valve via an AD/DA interface card and a PWM drive circuit with the sampling time of 1 ms. Thus, the solenoid force pulls the proportional valve inside the armature to move and the relationship between the command and the pressure on the calipers port at preloading (175 bars). The testing order is mainly step wave and triangular wave command-based since the step wave could confirm the reaction time, and the triangle wave could confirm the follow state and linearity.  
To verify the pressure relief performance of proportional valves, the single proportional valve must be tested to confirm the pressure relief function and facilitate the ABS wheel configuration design. Because the braking force is related to the brake pedal or handle brake of drivers, the caliper chamber pressure at each brake condition is tested with dissimilar initial pressures. In addition, the proportional solenoid is applied with 10 V to drive the single proportional valve for the maximum pressure relief test.  
Figure 20 shows the triangular wave command relief test results. When the power supplies 12 V (vehicle voltage), the proportional solenoid is not actuated at command 2.5 V or less, and the pressure drop is 130 bars above 10 V. The pressure drop between 2.5 V to 10 V is linear, and the relationship between voltage and pressure drop can be derived as 17.3 bars/V. The caliper pressure follows the command well and linearly, and the pressure does not have vibration when the valve is fully open. The solenoid force calculated as a result of the experiment is as follows:  
\[\frac{(\frac{175*\pi*0.18^{2}}{4}-F_{em})}{\frac{\pi}{4}(0.18^{2}-0.06^{2})}=45 \;\text{bars}\;\Rightarrow F_{em}=33.6\;N\]  
The calculated test result is greater than the simulated value (30 N).  
Figure 21 shows step wave command relief test results. It shows that when the voltage is lower than 3 V, the electromagnetic force is insufficient to open the valve port. The corresponding pressure drops for 3, 4.5, 6, 7.5, 9, and 10 V are, respectively, 25, 50, 75, 105, 125, and 130 bars. Figure 22 shows the time response when the step wave command is 10 V. The valve opening time is 9 ms (timing sequence from 8.821 s to 8.3 s) and the valve closing time is 5 ms (timing sequence from 9.321 s to 9.326 s).  
This proportional valve test meets with application requirements, and it can be used as a reference for the internal controller of the subsequent ABS module as the basis for the slip control calculation.  
Figure 19: Configuration of single proportional valve test: (**a**) test rig; and (**b**) structure.  
Figure 20: Triangular wave command at proportional valve relief test in 175 bars.