# An End-of-Line Test System for Pneumatic ABS Controllers in Commercial Vehicles
## 2 EOL Test Scheme Establishment  
The pneumatic ABS controller is a core component in electronic-controlled pneumatic braking systems. It can be divided into a software algorithm layer and hardware execution layer, as illustrated in Figure 1.  
During the braking process, the speed signal monitored by the wheel speed sensor is sent to the controller in real-time. After being processed by the conditioning circuit, the speed signal is utilized to judge the wheel rotation state and to calculate the slip ratio using a special algorithm. If the detected wheel slip ratio exceeds the safety threshold, then the driving unit of the controller will output pulse-width modulation (PWM) signals. The PWM signals will be shaped and amplified to drive the ABS valve to adjust the braking pressure. To verify the functions of the hardware execution layer and to quickly locate fault units under simulated operating environments, the EOL test system should be able to simulate the recommended test conditions (Table 1) and realize the rapid test condition configuration. According to IEEE24765 [10] and ISO26262 [11], the EOL test will verify the functions of each unit and carry out integration test for all units. Thus, the EOL test route was designed based on the unit integration test mode. During the unit testing process, communication verification between the test system and the controller was first implemented through the handshake protocol [12; 13]. After the communication unit had been qualified, the simulated wheel speed was generated according to the parameters of the target vehicle and the configured test conditions. Then, it was sent to the controller. After being processed, the wheel speed data feedback was sent \begin{table}
\begin{tabular}{c c c} \hline \hline
**No.** & **Test Conditions** & **Conditions Description** \\ \hline
1 & Straight-line braking test on single road &
\begin{tabular}{c} Braking test on high-adhesion or \\ low-adhesion road \\ \end{tabular} \\
2 & Adaptive test on bisectional road & Braking test on both sides of high-adhesion \\  & & and low-adhesion road \\
3 & Adaptive test on joint road & Braking test when driving from \\  & & high-adhesion to low-adhesion road \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Recommended test conditions in GB13594-2003. Figure 1: Framework of a pneumatic ABS controller. to the test system through the CAN (Controller Area Network) bus. Thus, the function of the wheel speed signal processing unit could be verified by comparing the data before and after transmission. Specific control instructions were generated according to the difference, and they were then sent to the corresponding units, i.e., the ABS valve drive unit, ABS switch function unit, and ABS indicator light control unit. The test system would check whether the output values were consistent with the expected ones. In the next stage, a functional integration test was carried out on the drive unit, the wheel speed processing unit, and the ABS switch function unit. Under simulated operation environments, the EOL test system output simulated wheel speed signals for the ABS controller as well as ABS valve theoretical drive signals for later comparisons. The functions of the ABS controller were verified by comparing the actual drive signals generated by the ABS controller with theoretical ones. The optimized EOL test workflow is shown in Figure 2.  
As shown in Figure 3, the designed EOL test system mainly includes hardware modules and embedded programs. Figure 3: Framework of an EOL test system for a control unit. Figure 2: Workflow of the EOL test. In the control unit, the I/O driver module outputs specific control signals; the A/D sampling module is responsible for collecting test signals; the A/O output module is used for the reoccurrence of the analog wheel speed signals; and the basic system module supplies an embedded hardware platform for the EOL test system, while the communication module supplies multiple communication interfaces that can support protocols such as CAN, K-line, RS232, and USB 3.0.