Zhenhai Gao - Jilin University
Jun Wang - Jilin University
Aixin Cui - Jilin University
Jian Guo - Jilin University
An ESP restrains a car’s yaw velocity within a small range by controlling the brake force and the engine’s output torque. The ESP helps the driver control the car by keeping the automobile balanced under extreme conditions and prevents dangerous accidents.
With the growing concern for proactive vehicle safety, many automobile manufacturers are equipping cars with ESP as a standard safety feature. Foreign suppliers of automotive electronic products, such as Bosch and Continental, can produce ESP on a large scale and occupy a major share of the market.
In China, we started ESP research later than other countries. Most of our research consists of studying theoretical control and hardware-in-the-loop (HIL) simulation. Most domestic whole-automobile or parts manufacturers simply purchase the ESP sold by Bosch, Continental, and TRW, then incorporate them into their automobiles.
Compared with domestic research on ESP strategy, the research on ESP system performance test and evaluation methods is in its early stages. Thus, most domestic experiments use testing methods from foreign parts manufacturers or corresponding institutions, or are directly delegated to foreign suppliers. So far, there is no common ESP standard in the domestic automobile industry, which makes it difficult for domestic whole-automobile manufacturers to systematically and reasonably evaluate ESP control performance. It is even more difficult to offer a complete set of product design requirements in the design phase using the testing outcomes. As a result, we experience a prolonged matching and designing phase, which increases the cost of research and development for the electronic control system of chassis between the whole-automobile manufacturers and automotive electronic parts suppliers.
Based on the current research, our research team created a complete set of performance evaluation methods and experiment procedures for the chassis’ electronic control system and developed a monitoring and control system for ESP performance testing and evaluation.
ESP Testing Platform
The ESP performance testing platform consists of three components:
1. ESP testing and experiment procedures
2. Data acquisition system
3. Experiment evaluation criteria, as shown in Figure 1
The testing and experiment procedures specify the experiment items, goals, variables, and instruments; experiment conditions and methods; and the experimental data processing methods.
The experiment evaluation criteria specify the methods and the corresponding principles to evaluate the electronic control system and performance of the vehicle using basic automobile theory.
Our experimental data acquisition system includes sensors, a data acquisition card, and software to measure the necessary variables (vehicle parameters and motion states) during the experiment. The performance of the experimental data acquisition system determines the accuracy of the automobile's performance evaluation results and the quality of the ESP.
As the latest automotive proactive safety system, ESP improves stability by accurately controlling an automobile on the verge of losing balance based on the automobile dynamics theory. Therefore, we need plenty of real automobile tests to evaluate ESP performance. There are two challenges for acquiring data from these tests: First, there is extensive testing equipment (GPS, gyroscope, noncontact photoelectric tachometer, wheel speed sensor, pressure sensor, trigger, and more, as shown in Figure 2); Second, the testing environment is harsh (impact, vibration, high temperature, high humidity, and so on). To mee these challenges we chose a testing platform based on LabVIEW and PXI.
The data acquisition hardware in the system includes NI PXI modules and sensors. Sensors and triggers are connected to the data acquisition module or chassis through terminal blocks and cables. We used an inverter to convert the 12 V DC of the in-vehicle power supply into 220 V AC to power the PXI chassis. To avoid sensor damage and error caused by voltage fluctuation, the 12 V DC is generated by the 220 V AC through a voltage stabilizer instead of connecting it directly to the battery on the vehicle. The structure of the power supply system is shown in Figure 3. The 220 V AC inverter and the PXI chassis are mounted on the aluminum alloy rack in the trunk. The rack is fixed to the vehicle body through bolts to prevent vibration, as shown in Figure 4.
We developed the data acquisition software using LabVIEW. With data acquisition modules and file I/O in LabVIEW, we acquired signals separately and stored them together. Because the sampling frequency is not very high (20 Hz) and synchronization is not strictly required, we used local variables to store signals from different channels. The structure of the program is shown in Figure 5.
The front panel of the ESP data acquisition system (Figure 6) is composed of two areas. The configuration area on the left is used for parameter input and modification, such as configuring data acquisition ports, deciding analog input (AI) channels, choosing RS232 ports, configuring baud rate, and changing the file name and path of the data file.
The real-time display area on the right is for monitoring key measurement results in the test. The curves of test results are shown in Figure 7 and Figure 8. The red spots in Figure 7 are the piles and the result indicates that the vehicle can pass all the piles of the single lane. The magenta curve in Figure 8 indicates whether the ESP functionality is activated, and the pressure of the main cylinder and all the wheel cylinders.
Proactive automobile safety systems, such as ESP, are a big part of the future for vehicle manufacturers. ESP road test is the ultimate way to evaluate the quality of the ESP control system, and also provides guidance to the development of the ESP control algorithm.
With the expansion capabilities of NI PXI, we rapidly created the platform to test the performance of ESP. In the extremely demanding testing environments, the testing system accurately and effectively acquires testing signals from the ESP experiment, which promotes the study of chassis control system and supports the improvement of the chassis’ electronic control system development.