Introduction to ESP system performance test system based on PXI platform

The Challenge:
The Electronic Stability Program (ESP) real vehicle road test is not only very demanding on the site, but also very dangerous during the test process, and requires many signals to be measured. The experimental data acquisition system must not only be able to collect various signals, but also be able to work stably and reliably in harsh test environments (such as impact, vibration, high temperature, high humidity, etc.).

The Solution:
Facing the harsh test environment and numerous test signals of the ESP system test, we quickly integrated the acquisition and processing of various signals such as analog signals, digital signals, CAN, and serial ports in a relatively short period of time based on the NI PXI and LabVIEW test platform. The NI data acquisition system successfully completed the data acquisition of the ESP test process at the Hainan test site, ensuring the smooth progress of the test.

"Based on the good scalability of the PXI system, we quickly built a test platform for ESP system performance testing."

The vehicle's electronic stability control system can assist the driver in controlling the vehicle's dynamic characteristics. By controlling the braking force of the wheels and the output torque of the engine, it can control the vehicle's yaw rate and limit the sideslip angle within a certain range, thereby helping the driver maintain the vehicle's stability under extreme conditions and preventing the vehicle from becoming unstable.

In recent years, with the increasing requirements for active vehicle safety and the promotion of corresponding safety regulations in various countries, the standard installation rate of ESP systems in automobiles has increased rapidly. Foreign automotive electronics suppliers such as Bosch and Continental have the ability to mass-produce ESP systems and have occupied a major share of the market.

The research on ESP systems in China started late, and mostly remains at the stage of theoretical control research and hardware-in-the-loop simulation. Most domestic vehicle and parts manufacturers directly adopt ESP systems from Bosch, Continental, TRW, etc. to match their independently developed vehicles.

Compared with the research on domestic ESP system strategies, the research on ESP system performance test and evaluation methods is basically blank. Most verification experiments refer to the test methods of foreign parts suppliers or relevant institutions or directly entrust the test to suppliers. At present, there is no unified ESP test standard in the domestic automobile industry, which makes it difficult for domestic vehicle manufacturers to systematically and reasonably evaluate ESP control performance, and it is even more difficult to put forward perfect product design technical requirements to automotive electronics suppliers at the product design stage based on the test results, which greatly increases the chassis electronic control system matching design cycle and R&D costs of vehicle manufacturers and automotive electronics suppliers.

In view of the above situation, the research team combined the current research foundation, proposed a set of automotive chassis electronic control system performance evaluation and experimental test process specifications, and built a measurement and control system platform for ESP system experimental testing.

ESP system test platform
The ESP system test platform built by the research team mainly includes three parts:

1. ESP test process specification;

2. Test data acquisition system;

3. Test evaluation criteria.

The test process specification specifies the test items, test objectives, test variables and instruments, test conditions, test methods, and experimental data processing methods required for ESP testing.

As a guide for evaluating the performance of electronic control systems and complete vehicles, the test evaluation standards specify the methods and corresponding principles for evaluating performance based on basic automobile-related theories.

The test data acquisition system includes sensors and data acquisition cards and related software that measure the required variables (vehicle parameters and motion status) during the test. The performance of the test data acquisition system determines to a certain extent whether the entire test system can accurately evaluate the performance of the vehicle and the quality of the ESP system. [page]

As the latest generation of active safety system for automobiles, ESP is a system that improves the stability of automobiles by accurately controlling the critical instability state of automobiles based on automobile dynamics. Therefore, in order to verify the performance of the ESP system, a large number of real vehicle tests are required. There are two major challenges in completing the test data collection: first, there are many test equipment (GPS, gyroscope, non-contact photoelectric speed meter, wheel speed sensor, pressure sensor, trigger, etc., as shown in Figure 2), and second, the test environment is harsh (shock, vibration, high temperature, high humidity, etc.). Through research, we chose the test platform of LabVIEW and PXI.

The data acquisition equipment relied on by the ESP test data acquisition system uses the NI PXI system and the corresponding PXI data acquisition card. The above system and the sensors required for the test constitute the hardware part of the ESP test data acquisition system. The sensors and triggers are connected to the acquisition card or chassis through the junction box and cables. In the process of building the hardware system, we encountered a problem: the PXI chassis we used requires 220V AC power supply, while the vehicle power supply in the test is a 12V DC battery. For this, we used an inverter to convert 12V DC into 220V AC, and then directly supply it to the PXI chassis. In order to avoid damage to the sensor caused by battery voltage fluctuations during the operation of the car and affect the measurement accuracy, the sensor power supply does not directly use the battery power supply, but converts 220VAC to 12VDC through a voltage regulator, and then supplies the corresponding sensor. The power system architecture is shown in Figure 3. The 220V AC inverter and PXI chassis are installed on the aluminum alloy bracket of the test vehicle trunk, as shown in Figure 4. The bracket is connected to the vehicle body floor by bolts to ensure that the chassis will not shake during the vehicle driving.

The data acquisition system software is implemented in LabVIEW, mainly using the data acquisition module and file IO module in LabVIEW. For many measurement signals, we adopted the architecture of collecting and storing each signal separately in programming. Since the sampling rate in the test is not high (20Hz), the signal synchronization requirement is not high, so local variables are used for synchronous storage of signals. The overall program framework is shown in Figure 5. The program front panel is shown in Figure 6. The front panel is mainly divided into two areas. The left area is the configuration area, which is mainly used for the quantities that need to be input and changed during the test, such as the configuration selection of the signal acquisition port, such as the selection of the analog input channel (AI), the selection of the RS232 port, the configuration of the baud rate, etc., as well as the change of the measurement result file name and the selection of the storage location. The right area is a real-time display of important detection quantities in the test, which is convenient for monitoring the test data during the test. When there are obvious errors in the test data, the instrument is adjusted or repaired in time, and the test is re-performed. Figures 7 and 8 are the test result curves. The red dots in Figure 7 are the stakes in the test. The results show that the vehicle can pass all the stakes in the single shift line smoothly. The magenta line in Figure 8 indicates whether the ESP function is activated, as well as the pressure of the brake master cylinder and each wheel cylinder.

in conclusion

ESP is a major development direction of future automotive active safety systems. ESP real-vehicle road tests are not only the ultimate means of judging the quality of ESP control systems, but also have certain guiding significance in the development stage of ESP control algorithms.

Based on the good scalability of the PXI system, we quickly built a test platform for the ESP system performance test. Under the extremely harsh test environments of the Hainan Automobile Test Field in summer and the Heihe Red River Valley Test Field in winter, the test system accurately and effectively collected the test signals of the ESP system test, which greatly promoted the research on the chassis control system of the 863 Plan and provided strong support for the further improvement of our independent chassis electronic control system.