## 4 Vehicle Test
### Construction of Detection System  
The real vehicle road test mainly obtains test data through the sensors installed on the vehicle. This test uses a VBOX measuring instrument, gyroscope, steering wheel sensor, test recorder, signal collector, pedal force sensor, brake trigger, power supply equipment and PC. The selected equipment is shown in Figure 2. The selected detection equipment can simultaneously detect the driving state and driving parameters of the tractor and the semi-trailer, including the displacement of the vehicle; the horizontal, vertical and pitch acceleration; the angular velocity; the yaw angle; the sideslip angle; the pitch angle; etc. Through these parameters, the stability of the semi-trailer train in the braking process can be judged in real time. The arrows in Figure 2 indicate the connections between the devices. \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline
**Parameter** & **Steering Axle** & **Driving Axle** & **Tractor Axle** \\ \hline Unsprung mass & 570 kg & 735 kg & 665 kg \\ Wheel track & 2030 mm & 1863 mm & 1863 mm & 1863 mm \\ Wheel center height & 510 mm & 530 mm & 530 mm & 530 mm \\ \hline \hline \end{tabular}
\end{table} 
Table 11: Axles parameter table. \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline
**Gear Position** & **R1** & **R2** & **1** & **2** & **3** & **4** & **5** & **6** & **7** & **8** & **9** & **10** \\ \hline \hline \multirow{2}{*}{Gear ratio} & 11.56 & 2.59 & 12.1 & 9.41 & 7.31 & 5.71 & 4.46 & 3.48 & 2.71 & 2.11 & 1.64 & 1.28 \\ \hline \hline \end{tabular}
\end{table} 
Table 10: Transmission speed ratio of each gear. \begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline
**Parameter** & **Steering Axle** & **Driving Axle** & **Tractor Axle** \\ \hline Unsprung mass & 570 kg & 735 kg & 665 kg \\ Wheel track & 2030 mm & 1863 mm & 1863 mm & 1863 mm \\ Wheel center height & 510 mm & 530 mm & 530 mm & 530 mm \\ \hline \hline \end{tabular}
\end{table} 
Table 11: Axles parameter table. The steering wheel angle sensor and measurement recorder can be used to test and record the steering wheel angle and rotational torque. One need only to fix the buckle on the vehicle steering wheel when using it. Its working principle is to use a high-precision photoelectric encoder to measure the angle of the steering wheel relative to the baseline. Since the steering wheel angle sensor itself is not equipped with a data storage reading module, the data need to be read and stored by an external test recorder. The steering wheel angle sensor is marked with a corner scale, and the angle of the steering wheel can also be read through the position indicated by the baseline pointer. The gyroscope integrates a three-coordinate inertial measurement unit, which is installed near the center of mass of the vehicle when used to measure the vehicle's position, speed, heading, vertical speed, lateral and longitudinal acceleration, roll angle, pitch angle, acceleration in the \(XYZ\) axis direction and other data. The braking strength can be tested by the brake pedal force sensor. Before the test, the brake trigger is posted on the pedal force sensor and the pedal force sensor is fixed on the driving brake pedal. At the same time, the brake trigger and the pedal force sensor are connected to the test recorder, which can detect the time at which the driver steps on the brake pedal and the size of the braking force in real time. The installation style is shown in Figure 3.  
In this paper, a VBOX II measuring instrument is used to track the GPS measurements of the semi-trailer train. Because of its small size and weight and its simple installation and operation, it is very suitable for vehicle dynamic detection. It is also mounted close to the center of mass of the vehicle when used.