Due to the characteristics of diesel engine with high torque and low fuel consumption, and with the development of modern diesel engine technology, the dieselization of the engine has become one of the energy saving and emission reduction measures. In order to control the emissions of diesel engines, under the already-enforced National III emission regulations, the scheme for realizing the electronic control of the automotive diesel engine is a clear optimal solution and development direction, that is, the electronic fuel injection system for diesel engines is required to completely replace the existing mechanical spray. Oil system. The diesel engine EFI technology belongs to the automobile core component technology and directly determines the emission and comprehensive performance level of the vehicle diesel engine. In the long-term goal of achieving “energy saving and emission reduction†in the country, the diesel engine EFI technology has become the most important issue that must be overcome before major domestic automobile engine companies.
At present, there are mainly four fuel system technical routes for domestic vehicle diesel engines for the implementation of the National III emission standards: electronically controlled pump nozzles (EUI), Common Rail, electronically controlled unit pumps (EUP), and electronically controlled inline trains. Pump (EIL) + EGR. Among these four technical routes, Delphi promotes common rail technology for medium- and light-duty vehicles in China, pump nozzles and single-pump technology for heavy-duty vehicles; Bosch pushes high-pressure common-rail systems in the Chinese market; and Denso is currently developing the third-generation technology. Generations, 4th-generation common-rail systems and common-rail systems for the Chinese market were adapted for secondary development; while ASIMCO Nanyue and Chengdu Witt, which are domestically-manufactured, proposed low-cost solutions for electronically controlled monomer pumps. Undoubtedly, the disputes over the technical routes of diesel fuel systems at home and abroad have now reached the stage of daylighting, and it is urgent for the people in the industry to think deeply about which technology solutions are most suitable for the fuel system technology market for the development of current and future diesel vehicles in China. Consider.
Electronically controlled pump nozzle technology
As early as 1905, Mr. Rudolf Diesel, the founder of the diesel engine, put forward the concept of the pump injector. He envisages that the injection pump and the nozzle are combined, eliminating the need for high-pressure fuel lines and obtaining high injection pressure. In the 1950s, diesel engines that intermittently controlled pump injection systems were used on ships and trucks. Since then, Volkswagen and Bosch have cooperated to develop a solenoid valve control pump injection system suitable for use in passenger cars. The car that matches the direct injection diesel engine has been significantly developed in Europe. The engine has high efficiency and excellent fuel economy, and reduces engine noise.
In the pump nozzle system, there is no pipe connection between the electronically controlled oil pump and the fuel injector, and the integral one is directly mounted on the cylinder head so that no more space is occupied. Each oil pump is driven by an overhead camshaft that simultaneously drives the valve and pump nozzles. The overhead camshaft must have extremely high stiffness and stiffness to withstand the high pressure generated by the injector. At the same time, the camshaft drive system also needs to be specially designed. The advantage of the electronically controlled pump nozzle system is that the system is compact and the nozzle aperture is very small, so the fuel injection pressure is very high, forming an excellent mixture, ensuring good atomization of the fuel, high combustion efficiency, and precise injection control. The starting point and fuel injection rate increase the power and fuel economy of diesel engines, reduce emissions and improve NVH characteristics. At present, the vehicle diesel engine adopting this technology can meet Euro IV emission standards and the peak pressure can reach 2000 bar.
The pump nozzle system is applied to direct injection diesel engines. The domestically produced 1.9TDI Bora engine uses this fuel injection system with a maximum injection pressure of 1800 bar. However, the disadvantage of the pump nozzle direct injection system is that the fuel injection pressure cannot be kept constant. Figure 1 shows Bosch's latest pump nozzle system and Figure 2 shows a schematic diagram of a commercial vehicle pump nozzle system.
Common Rail Technology
"CRDI" is the abbreviation of English Common Rail Direct Injection, which means high-pressure common rail diesel direct injection system. The system is mainly composed of high pressure oil pump, fuel injection pipe, high pressure accumulator (common rail), fuel injector, electronic control unit, sensors and actuators. In a closed-loop system consisting of a high-pressure oil pump, pressure sensor and ECU, the injection pressure is generated and the injection process is completely separated from each other. The high-pressure fuel pump delivers the high-pressure fuel to the common oil supply pipe and controls the opening time of the high-pressure oil pump solenoid valve so that the public The fuel pressure in the fuel supply pipe can be precisely controlled. By controlling the opening time and duration of the injector solenoid valve, the injection advance angle and the fuel injection amount can be controlled. The pressure of the high pressure tubing has nothing to do with the engine speed, which can greatly reduce the variation of the diesel fuel supply pressure with the engine speed, thereby improving the combustion process of the engine. While effectively reducing the engine emission level, it can also improve the engine's fuel economy. And reduce combustion noise. Figure 3 shows the schematic diagram of the electronically controlled high pressure common rail system. Figure 4 shows the working principle of the electronically controlled high pressure common rail system. The basic features of the system are:
(1) Compared with general mechanical in-line pump, the injection pressure is relatively high, and the current domestic maximum injection pressure can reach 1800 bar;
(2) Fuel injection pressure is independent of engine speed and can improve engine performance at low speeds and large loads;
(3) It can realize 5 injections, adjust the shape of fuel injection rate, and achieve the ideal fuel injection law;
(4) Fuel injection timing and fuel injection quantity can be freely set by ECU control;
(5) Small driving torque and better NVH index;
(6) The uniformity of the work of each cylinder can be corrected through the electronic control system;
(7) Fuel injection pressure adjustment range is wide, can adapt to various working conditions, and has good starting performance.
The disadvantages of the common rail system are:
(1) The key fuel injection technology is monopolized by a few foreign companies;
(2) Poor oil adaptability;
(3) The common rail system is not currently recognized by the market for reliability;
(4) The maintenance cost of the user is high. The failure of the common-rail engine electronic control system must rely on professional fault diagnosis equipment for inspection and maintenance, which is not good for long-distance transportation.
At present, major international auto parts suppliers are developing diesel common rail injection systems, such as: Bosch, Delphi, Siemens, Denso, VDO and Magna-Marelli, which are the world's leading suppliers of common rail injection systems. However, only Bosch is currently producing common rail diesel injection systems in China. Figure 5 shows Bosch's diesel engine electronically controlled common rail system simulation.
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Electronically controlled monomer pump technology
Monomer pump refers to a cylinder and an oil pump. Here, the oil pump refers to a high pressure oil pump, or an injection pump. The electronically controlled monomer pumping technology that has been well applied at home and abroad mainly includes a high-pressure oil pump with a discharge control valve, a mechanical injector, and a fuel line and a filter system required for connection. Its basic structure is that the oil pump plunger drive is integrated with the camshaft required by the engine valve mechanism to achieve the shortest possible fuel line from the oil pump to the injector. When the engine is running, numerous sensors are installed around the engine to detect the engine state, and the injection volume and injection timing of the injected cylinder are accurately and flexibly controlled. Through the optimization of the design of the electronic system and the oil pump structure, the fuel injection pressure of the fuel injection cylinder is increased, thereby improving the combustion process of the engine. While effectively reducing engine emission levels, the engine fuel economy and noise characteristics are improved. Figure 6 is a schematic diagram of a single pump system.
The main technical feature of the electronically controlled monomer pump technology is that the oil pump and the valve train share a single camshaft, which simplifies the structure and shortens the distance from the oil pump outlet to the injector. As the fuel valve is equipped with an electromagnetic valve capable of accurate fuel calculation and time control, the fuel injection timing and fuel injection amount can be controlled more accurately, which is beneficial to the optimization of the combustion process. As the principle of oil pump lift pressure is similar to that of an in-line pump, its injection pattern is characterized by a “triangular†front and rear emergency. It is beneficial to the optimization of the combustion process to a certain extent, and the maximum pressure can reach 1800-2000 bar. However, because the pressure of the oil pump is proportional to the engine speed, the pressure in the low speed region is low, which is not conducive to the improvement of the combustion performance of the diesel engine at low speed. In the phase III emission requirements of the country, the fuel injection opening method of the injector still depends on spring pressure control. In the phase IV of the country, the mechanical injectors need to be changed into electronic fuel injectors to form a dual solenoid valve unit pump system. The fuel injection pressure is increased to 2500 bar accordingly, and the system consistency control is used to optimize the entire injection process. And can achieve multiple injections. Without large adjustments to the overall engine structure, Euro IV emission levels can be achieved and the potential for Euro V emissions can be achieved.
The electronically controlled monomer pump system has been successfully used in Europe and America for more than ten years and is considered to be one of electronically controlled fuel injection systems with superior performance, stability, reliability, and long service life. In recent years, heavy-duty vehicle manufacturers in Europe and North America will still use the electronic unit pump system.
In the application of domestic products, taking into account the need to redesign the engine body to the existing engine casting, processing and production lines have great changes, in order to control the cost, generally used external plug-in single pump. However, this design will have some influence on noise and vibration. Figure 7 shows the external unit pump system for the V6 model.
In general, the electronically controlled monomer pump technology can achieve multiple injections by modifying the mechanical injector into a solenoid valve injector, which can meet the national III emission requirements and the future national IV emission control phase of the engine to the fuel system. Upgrade requirements. However, with regard to the measures required by the more stringent Euro V emission standards in Europe, trial production of electronically controlled monomer pump related systems is still in progress.
Electronically controlled inline pump + EGR technology
The electronically controlled inline pump + EGR technology is called the mechanical electronically controlled inline pump fuel injection system and the cooled electronically controlled EGR (exhaust gas recirculation) technology. The technology is controlled by the engine ECU (electrical control unit), through the intake air temperature sensor, intake pressure sensor, water temperature sensor, engine speed sensor, throttle sensor and vehicle brake signal to sense the various states of the engine, so as to control EGR The opening of the control valve and the exhaust gas recirculation ratio lead back part of the exhaust gas and fresh air into the cylinder of the engine to participate in combustion, which not only reduces the combustion temperature in the cylinder, but also effectively controls the generation of NOx under conditions of high temperature and oxygen enrichment, thereby reducing engine emissions. The NOx content in the.
The system uses an electronic fuel injection rate fuel injection pump, through the ECU control of the pre-stroke adjustment mechanism, to achieve precise control of fuel injection, injection timing and injection pressure. The pump has a pre-stroke electronically controlled adjustable structure, and its fuel supply pre-stroke can be electronically controlled by the ECU within a certain range. The pre-stroke can be changed according to the requirements of different working conditions of the diesel engine. By controlling the pre-stroke by the ECU, accurate injection timing and injection pressure can be obtained. At the same time with the throttle position sensor, so that the oil control more accurate, so as to ensure that the diesel engine can achieve the best economic performance and emissions throughout the entire operating range. The pump adopts 8-hole low inertia injector suitable for Euro III emission requirements. It features reliable operation, good performance and wide adaptability, which can effectively improve the combustion performance of the engine.
The economical and technical advantages of the electronically controlled in-line pump + EGR system engine are as follows:
(1) Short development cycle, low technology development and matching costs;
(2) The cost advantage of single machine is obvious;
(3) Good oil adaptability, low maintenance and maintenance costs, and low user cost;
(4) The fuel injection system is similar to the original State II mechanical fuel injection pump structure, and is easy to maintain;
(5) The EGR system is equipped with control valves and peak check valves to control the EGR rate at different loads.
At present, only China National Heavy Duty Truck has declared that it has an electronically controlled inline pump + EGR technology of the State III engine approved by an authoritative department. The built-in EGR State III engine developed by FAW has passed the bench test and submitted for approval. Companies such as Yuchai, Shangchai, Xichai, and Weichai are also developing EGR engines. The development cycle is about 36 months.
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Comparison and analysis
At present, from State II's entry into State III emission technology upgrades, the intention of the national policy orientation is to help companies and how they can smoothly upgrade to State III while minimizing development input costs. Each company can choose the technical route of its own country III product according to the characteristics of its own engine. The choices may not be the same, but the results achieved must be the same. The upgrade from State II to State III is indeed a qualitative change for the engine. However, this qualitative change is a change from a mechanical fuel injection system to an electronic control system, and it is not necessarily a transition to a specific fuel injection system. In terms of satisfying the National III standard, it is generally considered that the requirement is to use a single-cylinder four-valve technology. Through the optimization of the combustion chamber and exhaust gas treatment, the use of a mechanical pump can also meet Euro III emission regulations. At the end of the last century, European and American heavy-duty truck companies and engine companies took a variety of technological routes in the transition from Euro II to Euro III. They have adopted the common rail technology route, and also used pump nozzle technology and single pump technology, and also used machinery. Pumps to achieve State III emissions. A large number of domestic and foreign practical experiences and theoretical studies have shown that electronic control pump nozzle systems, electronically controlled high pressure common rail systems, electronic control unit pump systems, and electronically controlled inline pump systems all meet the current national III and future national IV emission requirements. ability. These four kinds of systems have advantages and disadvantages in terms of their respective structural features. No system can be said to be perfect, but each has its own characteristics. As far as the development of the domestic engine market is concerned, it is not necessarily a question of which technology route should be abandoned and what kind of technical route should be resolutely implemented. Instead, it needs to adapt measures to local conditions and avoid weaknesses. It must integrate cost, performance, matching and after-sales services. Analyze them so that they apply to engines of different types, conditions, and characteristics of use. China has vast territory, huge regional differences, unbalanced development of basic conditions, low quality of many users, and limited ability to accept new technologies. This series of objective reality requires that we must develop from China's development, application and promotion of new technologies. Starting from the national conditions, careful consideration, specific analysis and final decision-making. Table 1 lists the main feature comparisons and judgments of these four technologies for reference only.
The electronically controlled pump nozzle system and the electronically controlled high pressure common rail system can achieve high fuel injection pressures. The engine ECU can flexibly control the fuel distribution, fuel injection time, injection pressure and injection rate according to the requirements of the engine operating conditions to make the engine at a low speed. Complete combustion can also be achieved under operating conditions, with high torque output, efficient fuel economy, and excellent emissions performance, and the application of pre-injection and multi-injection technology also significantly reduces diesel engine noise and vibration. By controlling the above characteristics, the responsiveness and driving comfort of the diesel engine have reached the level of the gasoline engine. At the same time, it has significant fuel economy and low emission characteristics. As a passenger car market with relatively high requirements for noise and NVH characteristics and strong cost pressure, such as passenger cars and high-end light passenger vehicles are very suitable.
For the majority of our country's diesel engine market for light trucks, low-end light buses and construction machinery, due to the low price positioning of this type of vehicle, it is basically a production tool type application. When using electronically controlled pump nozzles, electronically controlled common rail systems, etc. In the case of the National III emission regulations, not only the development costs and production costs are unacceptable to the enterprise, but also the pressure on the company's after-sales service and maintenance links will be large; for the users, the requirements on the oil products and the use environment will also make them discouraged. . Therefore, comprehensively speaking, in the domestic market with a large number of light vehicles, the engine scheme based on the “electrically controlled inline pump + EGR†technology will be more appropriate. Its advantages lie in low technology development and matching costs, low stand-alone costs, good oil adaptability, and easy maintenance.
For medium-heavy trucks and large passenger vehicles, the use of electronically controlled monomer pumps or "electrically controlled inline pumps + EGR systems" will be a better choice. Its greatest advantage lies in the relatively simple structure, minor changes to the prototype engine, reliable performance, low failure rate, long life, and easy maintenance. There are cost advantages over common rails and pump nozzles, and both require less oil. It is more suitable for large-scale logistics and tourism market demand among domestic cities.
The field application classification of the above four technical solutions is more suitable for the development characteristics of our domestic market. It has good inheritance and practical significance for the domestic fuel injection system industry and the domestic diesel engine industry, and it also helps to improve China's automotive diesel engine. Market competitiveness.
Bangnuo Machinery Co., Ltd. , http://www.jsrollformingmachine.com