The automobile engine control module (PCM) is the control nerve center of the automobile, which directly affects the power, fuel economy and exhaust emissions of the automobile. With the development of the automotive electronics industry, PCM has become a standard configuration for automobiles. Because the PCM system is very complex, the working environment is extremely harsh, and its reliability is crucial, therefore, the PCM durability test is an important supporting condition for the development of PCM for automotive engines.
In the 1980s, several well-known international PCM module manufacturing companies, such as Bosch, Siemens, Delphi, and Visteon, successively conducted research on PCM durability testing technology for their products and developed corresponding equipment. Since this type of equipment still uses the design system more than 20 years ago, it has been unable to adapt to the rapid development of automotive EFI engine technology. The overall technical platform is backward, and there are some insurmountable defects, such as incompatibility with PCM modules from different manufacturers Set the automatic circulation strategy, can not configure the analog signal type and parameters on site. At present, China's self-developed automotive electronic products are in an accelerated development stage, but due to the late start of China's automobile industry, its own technology is backward, and its scientific research capabilities are not strong [1]. The existing PCM technology comes from abroad, and the durability test of PCM Technology is still a blank in China. Only a few colleges and universities have carried out researches on fault diagnosis, signal testing, running machine simulation, etc. around automotive EFI engines [2-4], and no complete technology has been formed.
This article introduces the overall design ideas and test specifications of the automotive PCM endurance test system, focusing on the design principles of key subsystems, and the long-term testing of several PCM modules through prototype prototypes to verify the reliability and versatility of the system .
2. Overall concept
2.1 Working principle of PCM
The automobile engine control module (PCM) is the core component of the automobile control system. It is mainly composed of five parts: input circuit, analog signal, digital signal converter, microcomputer, and output circuit. Its function is to receive various sensor signals, send instructions to the actuators through the calculation and processing of the microcomputer, connect the grounding wires of each actuator, make it work with electricity, and accurately control the fuel supply, ignition advance angle and idle air flow.
2.2 Design idea of ​​PCM durability test system
Based on the control technology of EFI engine, this paper uses a multi-layer CAN bus communication technology, virtual instrument technology and embedded computer system to design a universal open PCM durability test system. It is mainly composed of industrial control computer (industrial control computer), signal generation subsystem, analog load subsystem, load monitoring subsystem, high-power programmable power supply, environmental experiment box, field bus communication subsystem, application software and database management system. Its hardware system and prototype prototype are shown in Figures 1 and 2.
Figure 1 Hardware system of PCM endurance test general platform
Figure 2 Prototype of PCM durability test system
The test principle of the test system: Taking PCM as the test object, the industrial control computer sends setting instructions according to the test type and test items, controls the environmental variables and high-power DC power supply, quickly switches the car sensor signal and simulates the load connection, and promptly The load monitoring system sends a read command to monitor the PCM operating status online.
2.3 PCM durability test specification
The durability test specification is the basis of PCM durability test, which is related to the overall quality of PCM. In order to improve the reliability and durability of PCM during normal operation, a set of test specifications that can maximize the failure of PCM must be established. This system establishes the principles of durability test specifications: (1) Fully consider the various stress parameters that cause PCM failure; (2) Ensure sufficient test time to verify that the PCM module has sufficient reliability in the expected life [5].
According to the extreme environment under various working conditions of PCM, important parameters such as temperature, humidity and power supply voltage were determined, and a set of test specifications with a period of 6 hours were established, as shown in Figure 3, and the rapid development platform using DSPACE was adopted. Verification with the durability test experimental platform established with the NI virtual instrument platform.
(a) Temperature and humidity parameters
(b) Power supply parameters
Figure 3 Test specifications of relevant parameters
3. The main framework of the PCM durability test system
This system adopts Advantech industrial control computer, through the installation of conditioning amplifiers, A / D, D / A cards, installation of Visual C ++, LabVIEW and other development and application software, constitutes a virtual instrument platform, and realizes the fully digital acquisition test analysis of the computer. In addition, the system selected Agilent 6691A high-power programmable power supply for simulating the work of batteries and generators, and designed an environmental experiment box that can accommodate multiple PCMs.
3.1 Signal generation subsystem
In the related literature, the signal generating devices are only designed for specific PCM, and the flexibility is poor. The subsystem uses virtual instrument technology, and the main structure is an embedded computer system with ARM microcontroller and CPLD as the hardware framework. As long as it is assigned to different identification (ID) of each signal generation module, it can be expanded through the field bus to realize the multi-module signal generation subsystem network.
Using DDS technology is already a mainstream practice in the current test and measurement industry [6], and its frequency accuracy can be determined by the number of bits of the phase accumulator. This system uses a single chip + DDS chip to generate a sine signal. The principle is shown in Figure 4. The ARM single chip sends a control command to the CPLD. The CPLD decodes the clock to generate the DDS control signal and generates a sine wave of the corresponding frequency. Signal, the sinusoidal signal is filtered and amplified, and a sinusoidal signal of corresponding amplitude is output.
Figure 4 Schematic diagram of sinusoidal signal generation
Crankshaft position signal (CPS) is the most important sensor signal in the PCM control ignition system. In order to meet the needs of various PCMs, it is designed to generate CPLD and DA. The principle of CPS signal generation is shown in Figure 5. There is a cycle of sine table data in EPROM. When the CPS signal needs to be generated, the ARM microcontroller sets the CPLD. CPLD counts the clock and generates the read memory according to the received control command. And provide appropriate address signals and control signals to EPROM. EPROM outputs the data of the corresponding address, which is converted into a single-ended CPS analog signal by D / A conversion, and then outputs CPS through a filter circuit and a single-ended to differential processing circuit Differential signal. In the actual circuit implementation, the control of the CPS signal can be set by the computer to send a control command to the ARM through the CAN bus. Therefore, even if the ARM chip is reset during operation, the circuit can still output the correct CPS signal to ensure the test cycle Work properly.
The subsystem also designs two ways of generating VREF / 2 signals according to the needs of various PCM modules: resistance voltage division and operational amplifier voltage division; at the same time, a PWM generator is designed using a 555 time base circuit and a filter amplifier circuit ; In addition, the subsystem also uses a resistor divider plus integrated op amp isolation to generate a small amplitude fixed voltage signal (such as 1.0V) required by the PCM.
3.2 Simulated load subsystem 
Figure 5 CPS signal generation schematic
This subsystem mainly simulates the output loads such as the ignition coil, fuel injection, carbon valve of the canister, and exhaust gas recirculation connected to the PCM. The subsystem is an open load system that can simulate various PCM output loads, and can be expanded through a field bus.
This paper comprehensively analyzes the commonality and particularity of PCM load, and designs two types of load boards: common load board and special load board. The analog load module is composed of multiple analog load boards, and is installed in the load box together with the load monitoring module. When the test of specific items is required, the load switching can be completed through the relay matrix. In addition, the photoelectric isolation method is also used to convert the PCM output signal into a + 5V TTL signal that the load monitoring subsystem can receive. 3.3 Load monitoring subsystem
The subsystem is also an embedded computer system based on ARM single chip microcomputer and CPLD as the main hardware framework, and can be expanded through the field bus. The subsystem reads the monitoring signals in the simulated load subsystem in real time to monitor the changes of all load signals output by the PCM during the durability test, including the signal change period, the timing of the output of some important signals, etc., and the monitoring results , Upload to the industrial computer through the field bus.
Figure 6 The principle of ignition and fuel injection signal monitoring
Ignition and fuel injection signals are the key signals in automobile engines, and their cycle and timing are directly related to the running status of the car, so it is particularly important to monitor their cycle and timing. The monitoring principle diagram of this system is shown in Figure 6. The monitoring of the ignition signal is mainly to monitor its synchronization with the CPS signal and the timing relationship between two or four ignition signals. When the CPLD finds the starting point where the ignition signal is synchronized with the CPS, it counts each ignition signal according to the input PIP_IN signal. Whenever one ignition cycle is completed, an interrupt signal is generated to the ARM microcontroller in the next ignition cycle. The interrupt signal triggers the ARM MCU to enter the interrupt processing program. In this interrupt program, the ARM MCU reads the count value of each ignition signal, judges the timing and period of the ignition signal, and sets the flag of whether the ignition signal is normal or not. The monitoring of the fuel injection signal is mainly to monitor its synchronization with the CPS signal and the timing relationship between them. When the falling edge of any one of the four fuel injection signals in the PIP_IN signal arrives, CPLD will monitor the status of the other three fuel injection signals. If the other three fuel injection signals are in the normal state, the fuel injection signal normal sign will be given. , On the contrary, it gives abnormal sign of fuel injection signal.
For slow signals with a low frequency change (such as 2 Hz) in the PCM module, this system uses the RS232 bus read mode to monitor their periodic changes by the ARM.
3.4 Fieldbus communication subsystem
Since various subsystems of the entire system need to transfer large amounts of data in both directions, high demands are placed on the communication of the system: on the one hand, a higher communication rate; on the other hand, a more flexible protocol conversion . Because the CAN bus has outstanding reliability, real-time and flexibility, it has been widely recognized and used in the industry [7]. This system uses CAN bus as the main field, and also has K-LINE, GPIB, RS485, 245 bus field bus communication subsystem, and can flexibly form multiple communication subnets to complete the requirements of multi-module testing. This system uses two CAN subnets (CAN0, CAN1). For each PCM, the signal generation module, load monitoring module, and PCM form a communication subnet CAN 1. The industrial computer connects each subnet together through the communication subnet CAN0.
CAN communication between the signal generation subsystem and the industrial control computer: (1) Set the signal generation module, the setting range is mainly CPS type, start CPS, start sine signal generation and switch input relay; (2) control and read PCM failure Code. The signal generation module is a relay station for communication between the industrial computer and the PCM. When the industrial computer sets the PCM or reads the fault information of the PCM module during operation, it first sends an instruction to the signal generation module through CAN0. After the signal generation module receives the instruction, it only sends the ID to the PCM module after CAN ID change. Similarly, after receiving the CAN message returned by the PCM, the signal generation module only sends the ID to the industrial computer through CAN0 after the ID is changed. Considering the differences in communication interfaces of different PCM types, a KLIN bus is also added between the signal generation module and the PCM. When setting the PCM or reading the fault code of the PCM, the signal generation module receives the command through CAN0, converts it into a KLIN message, and sends it to the PCM module; in the same way, the KLIN message returned from the PCM is converted by the signal generation board into After CAN message, return to the industrial computer through CAN0.
CAN communication between the load monitoring subsystem and the industrial control computer: (1) Set the relay matrix. The industrial computer sends an instruction to set the relay matrix to the load monitoring module. After receiving the instruction, the load monitoring module transmits the relay matrix information to the corresponding analog load module; (2) Read the load monitoring information. When the system is working, the industrial control computer continuously sends an instruction to query the load monitoring module to the load monitoring module. After receiving the instruction, the load monitoring module combines the current PCM load monitoring data into a CAN message to the industrial control computer.
In addition, the simulated load subsystem is connected to the load monitoring subsystem through the RS245 bus, and relay matrix information is transmitted to each simulated load module to complete the load switching work; the high-power program-controlled power supply is connected to the industrial control computer through the GBIP and receives the power setting of the industrial control computer ; The environmental experiment box is connected to the industrial control computer through RS485, receives its setting commands, and adjusts the ambient temperature and humidity.
4 Conclusion
At present, the system has been successfully used in the PCM series of Changan CB, STC 1 ×× and 2 ×× series PCM durability test, verify the system's versatility and reliability. Because motorcycle PCM is similar to automobile PCM, it is also suitable for motorcycle PCM durability testing. Although the system may still have some defects, through continuous improvement and upgrading, it will surely provide a solid equipment guarantee for the development of automotive engine control systems.
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