Research on Intelligent Communication System of Vehicle Controllable Shock Absorber

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Research on Intelligent Communication System of Vehicle Controllable Shock Absorber [Copy link]

Abstract : This paper introduces the composition of an intelligent communication system for a controllable shock absorber. A single-chip microcomputer part for data acquisition is designed, and this module can automatically collect data that characterizes the working performance of the controllable shock absorber. At the same time, the software and hardware design methods for communication between the upper and lower computers are given, and the communication program between the upper and lower computers based on the serial port is provided by using the powerful instrument control and flexible programming capabilities of LabVIEW. Experiments show that the system can timely understand the working status of the controllable shock absorber.
Keywords : controllable shock absorber; serial communication; single-chip microcomputer; Labview

Introduction

With the development of modern automobile manufacturing technology, the speed of vehicles is getting higher and higher. When driving under different road conditions, the ride smoothness of vehicles varies greatly. In order to improve the ride smoothness of vehicles, more advanced vehicles are now equipped with controllable shock absorbers, which can automatically adjust the damping parameters of the controllable shock absorbers according to the driving conditions of the vehicle, thereby improving the ride smoothness of the whole vehicle. The
controllable shock absorber is the core component for improving the ride smoothness of the vehicle. Timely understanding the working parameters of the controllable shock absorber can effectively obtain the operating conditions of the whole vehicle. To this end, it is required to obtain the various working parameters of the vehicle's controllable shock absorber online and dynamically, and transmit the obtained data to the computer, perform simple data processing on the data, and help the driver determine whether it is necessary to adjust the damping performance of the controllable shock absorber according to the driving conditions [1].
Based on the working principle and characteristics of a vehicle's controllable shock absorber, this paper designs a single-chip microcomputer module for automatic data acquisition, which can automatically obtain the working parameters of the controllable shock absorber, and then transmit the data to the computer through the serial port, display and simply process the obtained data, and store the data at the same time.

1. Software and hardware design of the lower computer

1.1 Hardware composition and working principle of the lower computer
The main function of the lower computer of this system is to collect parameters that characterize the working performance of the controllable shock absorber online. Taking advantage of the flexible operation and simple structure of the single-chip microcomputer, the lower computer module is designed. The lower computer mainly consists of acquisition trigger, data storage, and data output conversion modules. The core of the acquisition trigger module is the timer/counter. This module allows the lower computer to collect the working parameters of the controllable shock absorber once at a certain time interval, thereby realizing the automatic sampling function of the lower computer; the data storage module uses AT24C256. AT24C256 is an erasable programmable read-only memory (EEPROM) with two address buses and a capacity of 256K bytes (32K*8). The EEPROM has a compact structure and is easy to expand. The steady-state circuit has a suitable trigger and filter input, which has a good noise suppression effect and can automatically complete data acquisition and storage [2]. The pin definition of this module is shown in Figure 1:

Figure 1 AT24C256 pin interface and definition
The functions of each pin are as follows:
DEVICES/PAGES ADDRESS (A1, A0) These two pins are the address lines of the module, and the capacity can be expanded.
SDA (SERIAL DATA) This pin is a bidirectional serial data transmission pin;
SCL (SERIAL CLOCK) When the pin is high, data enters the EEPROM, and when the pin is low, data is read out of the EEPROM;
WRITE PROTECT (WP) Write protection input interface, when this pin is connected to the GND pin, all normal reading and writing are allowed; when this pin is connected to the Vcc pin, all write operations to the chip are prohibited; if the pin is left floating, it will be automatically connected to GND internally. If the pin is connected to Vcc before the write operation, software write protection can be performed.
The EEPROM requires an 8-bit device address (DEVICE ADDRESS), followed by the start condition (START CONDITION), to determine the read or write state. The first 5 bits of the device address byte are fixed 1, 0 sequences. The device address format is as follows: A1, A0 are used to expand the EEPROM, and the last bit determines the read and write operations. High level - read; low level - write. If the above address is entered correctly, the EEPROM will output a 0 (ZERO), which is just a confirmation character to determine whether it can be read or written, otherwise it returns to the waiting state. The read and write operation format of AT24C256 is shown in Figure 2:

Figure 2 AT24C256 write and read operation formats

The MAX-485 module is a half-duplex module with a transmission speed of up to 2.5Mbps, 5V power supply support, and allows for large common-mode voltage signal input [3]. This module is mainly used to convert the level, converting the output TTL level of the AT24C256 to the 232 level or 485 level of the serial port communication to adapt to the data communication of the serial port.
1.2 Microcontroller read and write program and communication response program
The data read and write of the AT24C256 memory and its communication response program are all written in assembly language according to the read and write format of the AT24C256. Data acquisition is automatic. The read operation requires the host computer to send the command character DTxx (or DEXX), and the lower computer sends the collected record data to the serial port for the host computer to read.

2. Serial communication protocol and communication circuit

2.1 Serial communication protocol
Serial communication refers to the transmission of data by controlling instruments through the computer's serial port (COM). The advantage is that the standard port of the computer can be used without purchasing additional hardware communication equipment. There are different standards for serial communication. The most commonly used one is the standard of the Electronic Industries Association (EIA), called the RS-232 standard. This standard has two different interfaces: 25-pin and 9-pin. The 9-pin interface provides two data transmission lines (TXD, RXD) and 5 communication control lines (RTS, CTS, DSR, DCD, DTR). This is sufficient for general communication control, so most communications use a 9-pin communication interface. This system also uses a 9-pin standard interface. In serial communication, each character is transmitted in a package, called a data frame, which includes a data start bit, data, check bit, and stop flag bit [4]. All serial communication parameters in this system are set by default.
The RS-232 and RS-485 communication interface is shown in Figure 3: Among them, RS-232 transmits an unbalanced signal, and the data voltage on the interface is the relative voltage of TXD (2nd pin) relative to GND (5th pin) (9-pin connector), while the balanced differential signal transmission adopts two-wire transmission, forming a relative voltage on the two wires, which can resist interference, lightning strikes, etc., and allows a larger common mode voltage (Vcm). 32 transceiver modules can be connected to a multi-point network at the same time, with strong expansion capabilities. Figure 3 RS-232 and RS-485 transmission communication interface 2.2 Serial communication loop AT24C256 automatically collects and stores data at time intervals. The following work is to transfer the data to the computer's memory through the serial communication loop for further data display, data analysis and other follow-up work. The serial communication loop refers to the transmission channel for data from AT24C256 to the computer's memory. A simple schematic diagram is shown in Figure 4: Figure 4 Serial communication schematic diagram 3. Communication software design

The purpose of communication software is not only to complete communication, but also to consider the expansion of the system. The expansion of the system should not affect the working stability of the existing system. In order to complete the functions of the above software, we selected Labview, a popular virtual instrument programming software in the test field.
3.1 Labview [5]
The powerful and flexible instrument control function is the main feature that distinguishes Labview from other programming software. The Labview program has a hierarchical structure, which is conducive to the expansion of instrument functions. When the function of the instrument is increased, the function expansion of the instrument can be easily realized by adding functional subroutines to the main program.
In addition, Visa can be used to compile drivers for many special instruments. Visa is a general term for the standard I/O function library and its related specifications for instrument programming. For programmers, Visa is an API function interface that completes the instrument control function by calling low-level functions. Regardless of the interface, Visa can use the same operation to communicate with the instrument. Therefore, Visa can also meet the expansion of system functions in the future without affecting the overall structure of the program. Figure 5 Communication software flow chart 3.2 Communication software In the design of this communication software, we used the Visa described above to operate the computer serial port, so as to communicate and control with the lower computer of the intelligent control system. The program flow chart of the communication software is shown in Figure 5. Through the communication software, the upper computer sends a command string that meets the design requirements to the lower computer. After waiting for the response from the lower computer, the performance parameters representing the working condition of the controllable shock absorber that we need can be read from the lower computer. The front panel of the communication software is shown in Figure 6:





Figure 6 Communication software front panel
The upper part of the program front panel is the function selection control part of the program. By selecting the corresponding microcontroller, the required number of data, and correctly selecting and setting the serial port parameters, the write/read operation can obtain the performance parameters of the controllable shock absorber.
The lower part of the front panel is the data display part for obtaining the performance parameters of the controllable shock absorber. We will obtain the performance parameters of the controllable shock absorber, use the data chart to distinguish different parameters with different color curves, and can fully display the obtained data. In addition, we also use the form of a chart to display the data in a table. For future data processing or archiving, there is a storage link in the program, which can save the data to disk, and can be opened and browsed through a spreadsheet tool or notepad.

4 Conclusion

By designing a single-chip microcomputer, we have formed an automatic acquisition system for the performance parameters of the controllable shock absorber. It has a simple structure and is easy to expand, which can fully meet our design intentions. With the help of simple serial port communication, a reliable communication loop is established between the lower computer and the computer. With the assistance of powerful communication software, the intelligent communication test system has been debugged and tested, and has good working performance with the vehicle's controllable shock absorber. It has now been used on a certain type of vehicle as the control part of the controllable shock absorber.