With the advancement of technology, the digitization of automobiles is getting higher and higher. At present, automotive electronic information products have accounted for an average of 1/3 of the total cost of automobiles, and this ratio is still increasing. Some experts believe that this ratio will reach 40% in the next 10 years. For example, mid-range cars like Polaris have at least a dozen automotive electronic control units (ECUs). The so-called ECU is actually an embedded system with a single-chip computer. It has its own processor, I / O device and memory, and can independently control a certain system of the car, such as the engine management system EMS and ABS system. As for high-end cars, they often have dozens or even hundreds of ECUs, which are connected together through a digital bus structure to form a complex computer local area network.
1 Automotive ECU development process
1.1 V cycle method developed by automotive ECU
1.1.1 Design calculation
The purpose of the design calculation of the engine matching project is to determine the types and parameters of the engine and transmission components according to the performance required by the car. It is divided into the following three methods.
(1) Manual calculation
Mainly based on the balance diagram of the driving force and the exercise resistance of the car to determine the maximum speed, acceleration ability and climbing ability of the car in different gears, so as to evaluate the impact of the different transmission ratios of the transmission on the performance of the car, and determine the engine and transmission parameter. This method is cumbersome and the results are not accurate enough.
(2) Simulation calculation
On the basis of designing the model of the car and various parts, the performance parameters of the car parts such as the engine and transmission and the vehicle are input, the required driving cycle is specified, and finally the power, economy, emission performance and braking performance of the car are calculated. It can display and print various analysis reports and chart results on the computer. The calculation is fast and accurate, and it can reflect the impact of any parameter changes in the automotive system on the performance of the entire vehicle. At present, the common commercial vehicle simulation software in China is CRUISE, a vehicle performance simulation analysis software developed by Austria Liszt Internal Combustion Engine and Test Equipment Company (AVLLISTGmbH).
(3) Parameter optimization
Taking the power, economy, emission performance and braking performance of the car as the objective function, and the parameters such as engine power, car weight and transmission ratio of the transmission as the optimization variables, within a certain range, seek the optimal matching combination to The car achieves the best performance-price ratio.
1.1.2 Arrangement of engine and transmission
After completing the engine matching design calculation, based on the preliminary calculation parameters and car layout, one or more engines and transmissions can be selected from the market, and then the corresponding brake, steering and air conditioning system components can be selected and developed. Trial layout of cabin and bodywork. You can also build a CAD digital model of cars and parts, try to assemble in a CAD software environment, check for interference, and make adjustments. After determining the location of the main parts of the car, follow-up work can be carried out.
1.2 Development of engine accessory system
Generally, automobile engine suppliers only provide basic engines or engine bases, which lack some peripheral accessory systems, so automobile manufacturers are required to develop these systems. These accessory systems include: fans and fan clutches, intake and exhaust ducts, air filters, engine oil pumps, engine mounts, power steering pumps, three-way catalysts, air-conditioning compressors, and fuel supply systems.
1.3 Design and analysis
1.3.1 CAD design
In the development of modern automobiles, CAD software is needed to design digital models of automobiles and components.
The main car design CAD software are: Unigraphics of American UnigraphicsSoluTIons, Pro / ENGINEER of American ParametricTechnologyCorp, and CATIA of French DassauhSystems (Dassault).
The main CAD modeling methods are: feature modeling, reverse scanning with a coordinate measuring machine.
1.3.2 CAE analysis
The main automotive CAE analysis software includes: ANSYS series software of ANSYS (Anshi) Co., Ltd., Adams, Nastran and Patran of MSCSoftware, and Sysnoise, Falancs and Test.lab of LMS.
The CAE analysis items in the engine matching project include: engine noise and vibration analysis, engine support analysis, engine thermodynamic analysis, automobile crash analysis, and computational fluid dynamics analysis (verification of radiator size and engine intake flow characteristics).
1.4 Main test items
The main test items include: engine and automobile bench test, engine noise and vibration test, vibration test of engine mount, durability test of exhaust system, pressure and flow test of engine filter and cooling system.
2 Electric matching technology of engine
2.1 Engine management system and its development technology
2.1.1 Engine management system
The engine management system (EMS) is an integrated circuit system that integrates electronically controlled injection, emission control, electronic ignition, starting, anti-theft, and diagnostic functions based on the engine's electronic ignition and electronically controlled gasoline injection system. EMS can achieve precise and flexible control of various engine systems, and is the main means to improve engine performance indicators and emissions. The engine management system is composed of a microprocessor, various sensors, and actuators. The sensors detect various working states and parameters, and then the microprocessor issues instructions to each actuator to complete various actions after calculation, analysis, and judgment, so that The engine can work in the best condition under various working conditions.
2.1.2 Development technology of engine management system
Engine management system development technology involves many fields such as computer technology, automatic control, embedded system, engine technology, etc. It is the most complicated system in the automotive electrical control system. At present, automobile manufacturers do not need to develop EMS in the process of matching engine systems. This is because the basic engine usually provided by the engine supplier is already equipped with a ready-made EMS, and the car manufacturer only needs to contact the corresponding EMS developer for calibration.
The current popular EMS development process is to use visual and modular methods to build an engine control model on the MATLAB Simulink simulation computing platform. After successful debugging, compile it into machine execution code, and then download it to the automotive ECU. For example, the engine and car control system OpenECU development tool launched by British Pi Technology Company provides an automatic code generation and rapid prototyping solution. Its application range includes engine, transmission, chassis and hybrid control systems and automotive mass production systems. . The OpenECU platform can automatically generate control codes in the MATLAB Simulink environment and then run them in the automotive ECU.
2.2 Engine calibration technology
2.2.1 Engine calibration
Engine calibration test refers to the test technology that continuously adjusts the parameters of the engine management system under different working conditions and climate environments of the automobile to find a set of parameters under the optimal working state of the engine. It is usually divided into indoor bench test and outdoor road test. The outdoor road test is required to be carried out in the car test field, in addition to the "three high" test of "high cold, high temperature and high altitude". The main tools of engine calibration test are engine calibration software and engine calibration equipment.
Generally, the control algorithm software inside a certain type of engine ECU is fixed, but its thousands of free parameters are adjustable. For different models, these parameters need to be adjusted and optimized through engine matching calibration, so that the whole vehicle passes Various emission and driving performance indicators.
Matching calibration is a complicated system engineering. It includes bench tests, controlled environmental laboratory tests, calibration calculations based on mathematical models, emission tests, functional verification tests, etc. Throughout the entire engineering process, various advanced calibration tools (hardware equipment and computer software) must be formed to seamlessly connect the calibration system, including ECU communication, software programming, calibration parameter management, online calibration, temperature acquisition system, simulation Data acquisition system, etc.
2.2.2 Engine calibration software
Engine calibration software collects test data from engine sensors and writes (or downloads) them into the automotive ECU after technical processing. At the same time, due to the large amount of test data that needs to be processed during the calibration test, engine calibration software has a powerful database management Features. As the functions of modern engines are becoming more and more complex, the control parameters have also risen sharply from the initial dozen to the current thousands, which has led to a geometric progression in the number of tests. It is impossible to achieve the test of permutation and combination of all working conditions of each calibration parameter. Therefore, there is now a calibration software based on test optimization technology, such as MATLAB Model-based Calibration Toolbox (MBC) launched by MathWorks, which can optimize the test program, reduce the number of calibration tests, reduce test costs, and shorten the test cycle.
2.2.3 Engine calibration equipment
In the engine calibration test, it is necessary to measure various physical quantities such as engine speed, temperature, and pressure. In addition, the calibration data generated by the calibration software needs to be written into the automobile ECU. The engine calibration equipment can achieve these functions.
2.2.4 Engine calibration test
Engine bench calibration test items include: actual engine charging efficiency, air-fuel ratio, ignition timing, basic engine heat engine calibration; vehicle calibration test items include: vehicle exhaust emission control, vehicle drivability, tropical environment, plateau environment, cold zone Calibration and system verification of environment and vehicle parts fault diagnosis system.
3 Conclusion
At present, many development technologies in the field of engine matching still need to be assisted by foreign companies. Some technical concepts are also blank in automotive textbooks, such as the development and calibration technology of engine management systems. The author hopes that this article can play a role in providing a reference for domestic auto manufacturers to develop new models.
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